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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>
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snhenson authored and mattcaswell committed Aug 23, 2016
1 parent 3cb28d1 commit baaabfd8fdcec04a691695fad9a664bea43202b6
Showing with 8 additions and 3 deletions.
  1. +8 −3 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

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