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 938f8be..b8f8fd2 100644
--- a/ssl/t1_lib.c
+++ b/ssl/t1_lib.c
@@ -2969,9 +2969,7 @@
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)
@@ -3018,6 +3016,12 @@
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
