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Fix protocol downgrade bug in case of fragmented packets

Browse source 
CVE-2014-3511

Reviewed-by: Emilia Käsper <emilia@openssl.org>
Reviewed-by: Bodo Möller <bodo@openssl.org>
This commit is contained in:
David Benjamin 2014-07-23 22:32:21 +02:00 committed by Matt Caswell
parent d345a24569
commit 40a2200d89
1 changed files with 23 additions and 7 deletions
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30
ssl/s23_srvr.c
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@ -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 */
@ -451,14 +447,34 @@ 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);