Fix potential DoS issue with p2c header

Unbounded p2c headers may be used to cause an application that accept
PBES algorithms to spend a lot of resources running PBKDF2 with a very
high number of iterations.

Limit the maximum number of iterations to to 32768.

Fixes: CVE-2023-50967

Signed-off-by: Sergio Correia <[email protected]>

lib/openssl/pbes2.c

@@ -25,6 +25,8 @@
 #include <string.h>
 
 #define NAMES "PBES2-HS256+A128KW", "PBES2-HS384+A192KW", "PBES2-HS512+A256KW"
+#define P2C_MIN_ITERATIONS 1000
+#define P2C_MAX_ITERATIONS 32768
 
 static json_t *
 pbkdf2(const char *alg, jose_cfg_t *cfg, const json_t *jwk, int iter,
@@ -193,7 +195,7 @@ alg_wrap_wrp(const jose_hook_alg_t *alg, jose_cfg_t *cfg, json_t *jwe,
     json_auto_t *hdr = NULL;
     const char *aes = NULL;
     json_t *h = NULL;
-    int p2c = 10000;
+    int p2c = P2C_MAX_ITERATIONS;
     size_t stl = 0;
 
     if (!json_object_get(cek, "k") && !jose_jwk_gen(cfg, cek))
@@ -226,7 +228,7 @@ alg_wrap_wrp(const jose_hook_alg_t *alg, jose_cfg_t *cfg, json_t *jwe,
         json_object_set_new(h, "p2c", json_integer(p2c)) < 0)
         return false;
 
-    if (p2c < 1000)
+    if (p2c < P2C_MIN_ITERATIONS || p2c > P2C_MAX_ITERATIONS)
         return false;
 
     if (json_object_set_new(h, "p2s", jose_b64_enc(st, stl)) == -1)
@@ -268,6 +270,9 @@ alg_wrap_unw(const jose_hook_alg_t *alg, jose_cfg_t *cfg, const json_t *jwe,
     if (json_unpack(hdr, "{s:I}", "p2c", &p2c) == -1)
         return false;
 
+    if (p2c > P2C_MAX_ITERATIONS)
+        return false;
+
     stl = jose_b64_dec(json_object_get(hdr, "p2s"), NULL, 0);
     if (stl < 8 || stl > sizeof(st))
         return false;

tests/cve-2023-50967/cve-2023-50967.jwe

@@ -0,0 +1 @@
+{"ciphertext":"aaPb-JYGACs-loPwJkZewg","encrypted_key":"P1h8q8wLVxqYsZUuw6iEQTzgXVZHCsu8Eik-oqbE4AJGIDto3gb3SA","header":{"alg":"PBES2-HS256+A128KW","p2c":1000000000,"p2s":"qUQQWWkyyIqculSiC93mlg"},"iv":"Clg3JX9oNl_ck3sLSGrlgg","protected":"eyJlbmMiOiJBMTI4Q0JDLUhTMjU2In0","tag":"i7vga9tJkwRswFd7HlyD_A"}

tests/cve-2023-50967/cve-2023-50967.jwk

@@ -0,0 +1 @@
+{"alg":"PBES2-HS256+A128KW","k":"VHBLJ4-PmnqELoKbQoXuRA","key_ops":["wrapKey","unwrapKey"],"kty":"oct"}

tests/jose-jwe-dec

@@ -53,3 +53,8 @@ test "`jose jwe dec -i $prfx.12.jweg -k $prfx.12.jwk`"   = "`cat $prfx.12.pt`"
 test "`jose jwe dec -i $prfx.13.jweg -k $prfx.13.1.jwk`" = "`cat $prfx.13.pt`"
 test "`jose jwe dec -i $prfx.13.jweg -k $prfx.13.2.jwk`" = "`cat $prfx.13.pt`"
 test "`jose jwe dec -i $prfx.13.jweg -k $prfx.13.3.jwk`" = "`cat $prfx.13.pt`"
+
+# CVE-2023-50967 - test originally from https://github.com/P3ngu1nW/CVE_Request/blob/main/latch-jose.md
+# This test is expected to fail quickly on patched systems.
+prfx="${CVE_2023_50967}/cve-2023-50967"
+! test "$(jose jwe dec -i $prfx.jwe -k $prfx.jwk)"

tests/meson.build

@@ -31,6 +31,8 @@ progs = [
 e = environment()
 e.prepend('PATH', meson.current_build_dir() + '/../cmd', separator: ':')
 e.set('VECTORS', meson.current_source_dir() + '/vectors')
+e.set('CVE_2023_50967', meson.current_source_dir() + '/cve-2023-50967')
+
 
 foreach p: progs
   exe = executable(p, p + '.c', dependencies: libjose_dep)