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From fc4f4cdb8bf9981904e652abf69b892a45bddacf Mon Sep 17 00:00:00 2001
From: David Benjamin <davidben@google.com>
Date: Wed, 23 Jul 2014 22:32:21 +0200
Subject: [PATCH] Fix protocol downgrade bug in case of fragmented packets
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit
CVE-2014-3511
Reviewed-by: Emilia Käsper <emilia@openssl.org>
Reviewed-by: Bodo Möller <bodo@openssl.org>
---
ssl/s23_srvr.c | 30 +++++++++++++++++++++++-------
1 file changed, 23 insertions(+), 7 deletions(-)
diff --git a/ssl/s23_srvr.c b/ssl/s23_srvr.c
index 4877849..2901a6b 100644
--- a/a/ssl/s23_srvr.c
+++ b/b/ssl/s23_srvr.c
@@ -348,23 +348,19 @@ int ssl23_get_client_hello(SSL *s)
* Client Hello message, this would be difficult, and we'd have
* to read more records to find out.
* No known SSL 3.0 client fragments ClientHello like this,
- * so we simply assume TLS 1.0 to avoid protocol version downgrade
- * attacks. */
+ * so we simply reject such connections to avoid
+ * protocol version downgrade attacks. */
if (p[3] == 0 && p[4] < 6)
{
-#if 0
SSLerr(SSL_F_SSL23_GET_CLIENT_HELLO,SSL_R_RECORD_TOO_SMALL);
goto err;
-#else
- v[1] = TLS1_VERSION_MINOR;
-#endif
}
/* if major version number > 3 set minor to a value
* which will use the highest version 3 we support.
* If TLS 2.0 ever appears we will need to revise
* this....
*/
- else if (p[9] > SSL3_VERSION_MAJOR)
+ if (p[9] > SSL3_VERSION_MAJOR)
v[1]=0xff;
else
v[1]=p[10]; /* minor version according to client_version */
@@ -444,14 +440,34 @@ int ssl23_get_client_hello(SSL *s)
v[0] = p[3]; /* == SSL3_VERSION_MAJOR */
v[1] = p[4];
+ /* An SSLv3/TLSv1 backwards-compatible CLIENT-HELLO in an SSLv2
+ * header is sent directly on the wire, not wrapped as a TLS
+ * record. It's format is:
+ * Byte Content
+ * 0-1 msg_length
+ * 2 msg_type
+ * 3-4 version
+ * 5-6 cipher_spec_length
+ * 7-8 session_id_length
+ * 9-10 challenge_length
+ * ... ...
+ */
n=((p[0]&0x7f)<<8)|p[1];
if (n > (1024*4))
{
SSLerr(SSL_F_SSL23_GET_CLIENT_HELLO,SSL_R_RECORD_TOO_LARGE);
goto err;
}
+ if (n < 9)
+ {
+ SSLerr(SSL_F_SSL23_GET_CLIENT_HELLO,SSL_R_RECORD_LENGTH_MISMATCH);
+ goto err;
+ }
j=ssl23_read_bytes(s,n+2);
+ /* We previously read 11 bytes, so if j > 0, we must have
+ * j == n+2 == s->packet_length. We have at least 11 valid
+ * packet bytes. */
if (j <= 0) return(j);
ssl3_finish_mac(s, s->packet+2, s->packet_length-2);
--
1.8.3.1
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