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From 1bbe48ab149893a78bf99c8eb8895c928900a16f Mon Sep 17 00:00:00 2001
From: "Dr. Stephen Henson" <steve@openssl.org>
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 <rsalz@openssl.org>
(cherry picked from commit baaabfd8fdcec04a691695fad9a664bea43202b6)
---
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 d961e4a..7680491 100644
--- a/ssl/t1_lib.c
+++ b/ssl/t1_lib.c
@@ -2273,9 +2273,7 @@ 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);
@@ -2309,6 +2307,13 @@ 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
--
1.9.1
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