From baaabfd8fdcec04a691695fad9a664bea43202b6 Mon Sep 17 00:00:00 2001 From: "Dr. Stephen Henson" Date: Tue, 23 Aug 2016 18:14:54 +0100 Subject: [PATCH] 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 --- ssl/t1_lib.c | 11 ++++++++--- 1 file changed, 8 insertions(+), 3 deletions(-) diff --git a/ssl/t1_lib.c b/ssl/t1_lib.c index 7d322d0253..fbcf2e663c 100644 --- 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 -- 2.25.1