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: Viktor Dukhovni <viktor@openssl.org>

diff --git a/ssl/t1_lib.c b/ssl/t1_lib.c
index 938f8be15f7c9977ee991fe0be7985eb1e4b0bc7..b8f8fd22fe91dccabbea092bac0d66baa7500172 100644 (file)
--- a/ssl/t1_lib.c
+++ b/ssl/t1_lib.c
@@ -2969,9 +2969,7 @@ static int tls_decrypt_ticket(SSL *s, const unsigned char *etick,
     HMAC_CTX *hctx = NULL;
     EVP_CIPHER_CTX *ctx;
     SSL_CTX *tctx = s->initial_ctx;
     HMAC_CTX *hctx = NULL;
     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 */
     hctx = HMAC_CTX_new();
     if (hctx == NULL)
     /* Initialize session ticket encryption and HMAC contexts */
     hctx = HMAC_CTX_new();
     if (hctx == NULL)


@@ -3018,6 +3016,12 @@ static int tls_decrypt_ticket(SSL *s, const unsigned char *etick,
     if (mlen < 0) {
         goto err;
     }
     if (mlen < 0) {
         goto err;
     }

+    /* Sanity check ticket length: must exceed keyname + IV + HMAC */
+    if (eticklen <=
+        TLSEXT_KEYNAME_LENGTH + EVP_CIPHER_CTX_iv_length(ctx) + mlen) {
+        ret = 2;
+        goto err;
+    }

     eticklen -= mlen;
     /* Check HMAC of encrypted ticket */
     if (HMAC_Update(hctx, etick, eticklen) <= 0
     eticklen -= mlen;
     /* Check HMAC of encrypted ticket */
     if (HMAC_Update(hctx, etick, eticklen) <= 0