Sanity check ticket length.

If a ticket callback changes the HMAC digest to SHA512 the existing
sanity checks are not sufficient and an attacker could perform a DoS
attack with a malformed ticket. Add additional checks based on
HMAC size.

Thanks to Shi Lei for reporting this bug.

CVE-2016-6302

Reviewed-by: Rich Salz <rsalz@openssl.org>
(cherry picked from commit baaabfd8fdcec04a691695fad9a664bea43202b6)

diff --git a/ssl/t1_lib.c b/ssl/t1_lib.c
index d961e4afb504e9e705f2fbe3868c5dfa731a4db3..76804913400807d18eabad22de5b0a4d7bd840ef 100644 (file)
--- a/ssl/t1_lib.c
+++ b/ssl/t1_lib.c
@@ -2273,9 +2273,7 @@ static int tls_decrypt_ticket(SSL *s, const unsigned char *etick,
     HMAC_CTX hctx;
     EVP_CIPHER_CTX ctx;
     SSL_CTX *tctx = s->initial_ctx;
-    /* Need at least keyname + iv + some encrypted data */
-    if (eticklen < 48)
-        return 2;
+
     /* Initialize session ticket encryption and HMAC contexts */
     HMAC_CTX_init(&hctx);
     EVP_CIPHER_CTX_init(&ctx);
@@ -2309,6 +2307,13 @@ static int tls_decrypt_ticket(SSL *s, const unsigned char *etick,
     if (mlen < 0) {
         goto err;
     }
+    /* Sanity check ticket length: must exceed keyname + IV + HMAC */
+    if (eticklen <= 16 + EVP_CIPHER_CTX_iv_length(&ctx) + mlen) {
+        HMAC_CTX_cleanup(&hctx);
+        EVP_CIPHER_CTX_cleanup(&ctx);
+        return 2;
+    }
+
     eticklen -= mlen;
     /* Check HMAC of encrypted ticket */
     if (HMAC_Update(&hctx, etick, eticklen) <= 0