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>
openssl · Aug 23, 2016 · baaabfd · baaabfd
1 parent 3cb28d1
commit baaabfd
Showing 1 changed file with 8 additions and 3 deletions.
diff --git a/ssl/t1_lib.c b/ssl/t1_lib.c
@@ -3401,9 +3401,7 @@ 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);
@@ -3437,6 +3435,13 @@ 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