Impact
This vulnerability applies to all users of:
org.http4s.server.staticcontent.FileServiceorg.http4s.server.staticcontent.ResourceServiceorg.http4s.server.staticcontent.WebjarService
Path escaping
URI normalization is applied incorrectly. Requests whose path info contain ../ or // can expose resources outside of the configured location. Specifically:
FileService may expose any file on the local file system.ResourceService may expose any resource on the class path.
Prefix matching
When the service is configured with a non-empty pathPrefix that doesn't end in a slash, any directories whose names are a prefix of systemPath (from FileService) or pathPrefix (from ResourceService) are exposed. For example, if pathPrefix is /foo and systemPath is /bar, a request to /foobaz/quux.txt exposes file /barbaz/quux.txt, when only files beneath /bar should be available.
URI decoding
URI segments are not decoded before resource resolution. This causes resources with reserved characters in their name to incorrectly return a 404. It also may incorrectly expose the rare resource whose name is URI encoded. This applies to FileService, ResourceService, and WebjarService.
Patches
In all three services, paths with an empty segment, a . segment, or a .. segment are now rejected with a 400 Bad Request response. This fixes exposure outside the configured root. Many clients already eliminate dot segments according to the rules in RFC3986, Section 5.2.4. A middleware that does so at the server level may be considered if there is demand.
If pathInfo is non-empty, and does not begin with /, then a 404 response is generated. This fixes the prefix matching exposure.
All path segments are URI decoded before being passed to the file system or resource path. This allows resolution of resources with reserved characters in the name, and prevents incorrect exposure of resources whose names are themselves URI encoded.
Workarounds
The recommended course is to upgrade:
- v0.18.26, binary compatible with the 0.18.x series
- v0.20.20, binary compatible with the 0.20.x series
- v0.21.2, binary compatible with the 0.21.x series
Note that 0.19.0 is a deprecated release and has never been supported.
If an upgrade is impossible:
- Temporarily copy
FileService.scala, ResourceService.scala, and WebjarService.scala from the appropriate release series into your project and recompile with that, changing the package name and reference in your application.
- Users of a servlet backend can use the servlet container's file serving capabilities.
Credits
Thank you to Thomas Gøytil for the discovery, responsible disclosure, and assistance testing of this vulnerability.
For more information
If you have any questions or comments about this advisory:
References
Impact
This vulnerability applies to all users of:
org.http4s.server.staticcontent.FileServiceorg.http4s.server.staticcontent.ResourceServiceorg.http4s.server.staticcontent.WebjarServicePath escaping
URI normalization is applied incorrectly. Requests whose path info contain
../or//can expose resources outside of the configured location. Specifically:FileServicemay expose any file on the local file system.ResourceServicemay expose any resource on the class path.Prefix matching
When the service is configured with a non-empty
pathPrefixthat doesn't end in a slash, any directories whose names are a prefix ofsystemPath(fromFileService) orpathPrefix(fromResourceService) are exposed. For example, ifpathPrefixis/fooandsystemPathis/bar, a request to/foobaz/quux.txtexposes file/barbaz/quux.txt, when only files beneath/barshould be available.URI decoding
URI segments are not decoded before resource resolution. This causes resources with reserved characters in their name to incorrectly return a 404. It also may incorrectly expose the rare resource whose name is URI encoded. This applies to
FileService,ResourceService, andWebjarService.Patches
In all three services, paths with an empty segment, a
.segment, or a..segment are now rejected with a400 Bad Requestresponse. This fixes exposure outside the configured root. Many clients already eliminate dot segments according to the rules in RFC3986, Section 5.2.4. A middleware that does so at the server level may be considered if there is demand.If
pathInfois non-empty, and does not begin with/, then a 404 response is generated. This fixes the prefix matching exposure.All path segments are URI decoded before being passed to the file system or resource path. This allows resolution of resources with reserved characters in the name, and prevents incorrect exposure of resources whose names are themselves URI encoded.
Workarounds
The recommended course is to upgrade:
Note that 0.19.0 is a deprecated release and has never been supported.
If an upgrade is impossible:
FileService.scala,ResourceService.scala, andWebjarService.scalafrom the appropriate release series into your project and recompile with that, changing the package name and reference in your application.Credits
Thank you to Thomas Gøytil for the discovery, responsible disclosure, and assistance testing of this vulnerability.
For more information
If you have any questions or comments about this advisory:
References