[Security] OpenSSH 6.4

[interfasys]

You need to install OpenSSH ASAP if you're affected or use the patch below

This document may be found at: http://www.openssh.com/txt/gcmrekey.adv
1. Vulnerability

A memory corruption vulnerability exists in the post-
authentication sshd process when an AES-GCM cipher
([email protected] or [email protected]) is
selected during kex exchange.

If exploited, this vulnerability might permit code execution
with the privileges of the authenticated user and may
therefore allow bypassing restricted shell/command
configurations.

2. Affected configurations

OpenSSH 6.2 and OpenSSH 6.3 when built against an OpenSSL
that supports AES-GCM.

3. Mitigation

Disable AES-GCM in the server configuration. The following
sshd_config option will disable AES-GCM while leaving other
ciphers active:

Ciphers aes128-ctr,aes192-ctr,aes256-ctr,aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,aes192-cbc,aes256-cbc

4. Details

When using AES-GCM, sshd was not initialising a Message
Authentication Code (MAC) context that is unused when the
cipher mode offers authentication itself. This context
contains some callback pointers, including a cleanup callback
that was still being invoked during a rekeying operation.
As such, the address being called was derived from previous
heap contents.

This vulnerability is mitigated by the difficulty of
pre-loading the heap with a useful callback address and by
any platform address-space layout randomisation applied to
sshd and the shared libraries it depends upon.

5. Credit

This issue was identified by Markus Friedl (an OpenSSH
developer) on November 7th, 2013.

6. Fix

OpenSSH 6.4 contains a fix for this vulnerability. Users who
prefer to continue to use OpenSSH 6.2 or 6.3 may apply this
patch:

Index: monitor_wrap.c
===================================================================
RCS file: /cvs/src/usr.bin/ssh/monitor_wrap.c,v
retrieving revision 1.76
diff -u -p -u -r1.76 monitor_wrap.c
--- monitor_wrap.c 17 May 2013 00:13:13 -0000 1.76
+++ monitor_wrap.c 6 Nov 2013 16:31:26 -0000
@@ -469,7 +469,7 @@ mm_newkeys_from_blob(u_char *blob, int b
buffer_init(&b);
buffer_append(&b, blob, blen);

- newkey = xmalloc(sizeof(*newkey));
+ newkey = xcalloc(1, sizeof(*newkey));
enc = &newkey->enc;
mac = &newkey->mac;
comp = &newkey->comp;

 

[Active8]

Is this available in Custom Build ?

 

[DirectAdmin Support]

Hello,

Unfortunately not.
DirectAdmin and CustomBuild do not manage low level services and libraries like openssl, openssh, etc..

I'm also not sure if many people would be affected.
Check your version of openssh with:

sshd -v

John

 

[ccto]

CentOS 6.4 ships sshd 5.3p1 , which does not contain the said chiper AES-GCM in OpenSSL
CentOS 5.10 ships with OpenSSH_4.3p2,, also does not have the said chiper AES-GCM in OpenSSL too

It shall be safe by default, am I ?

 

[ben29]

red hat, will need to do update , but before that they test it, after that , it will be avisable to update from your os by "yum "

 

[wattie]

FreeBSD 9.1 is using OpenSSH 5.8