Bug 1238231 (CVE-2015-5352) - CVE-2015-5352 openssh: XSECURITY restrictions bypass under certain conditions in ssh(1)
Summary: CVE-2015-5352 openssh: XSECURITY restrictions bypass under certain conditions...
Keywords:
Status: CLOSED ERRATA
Alias: CVE-2015-5352
Product: Security Response
Classification: Other
Component: vulnerability
Version: unspecified
Hardware: All
OS: Linux
medium
medium
Target Milestone: ---
Assignee: Red Hat Product Security
QA Contact:
URL:
Whiteboard:
Depends On: 1238241 1247864 1281468
Blocks: 1210268 1252864 1278736
TreeView+ depends on / blocked
 
Reported: 2015-07-01 12:42 UTC by Vasyl Kaigorodov
Modified: 2021-02-17 05:10 UTC (History)
16 users (show)

Fixed In Version: OpenSSH 6.9
Doc Type: Bug Fix
Doc Text:
It was found that the OpenSSH client did not properly enforce the ForwardX11Timeout setting. A malicious or compromised remote X application could possibly use this flaw to establish a trusted connection to the local X server, even if only untrusted X11 forwarding was requested.
Clone Of:
Environment:
Last Closed: 2016-05-11 06:45:31 UTC
Embargoed:

Attachments (Terms of Use)


Links
System ID Private Priority Status Summary Last Updated
Red Hat Bugzilla 1255275 1 None None None 2021-01-20 06:05:38 UTC
Red Hat Product Errata RHSA-2016:0741 0 normal SHIPPED_LIVE Moderate: openssh security, bug fix, and enhancement update 2016-05-10 22:29:45 UTC

Internal Links: 1255275

Description Vasyl Kaigorodov 2015-07-01 12:42:20 UTC 
It was reported that when forwarding X11 connections with ForwardX11Trusted=no, connections made after ForwardX11Timeout expired could be permitted and no longer subject to XSECURITY restrictions because of an ineffective timeout check in ssh(1) coupled with "fail open" behaviour in the X11 server when clients attempted connections with expired credentials. This problem was reported by Jann Horn.

Upstream patches:

http://cvsweb.openbsd.org/cgi-bin/cvsweb/src/usr.bin/ssh/channels.c#rev1.347
http://cvsweb.openbsd.org/cgi-bin/cvsweb/src/usr.bin/ssh/clientloop.c#rev1.274

Portable OpenSSH git commit with both above changes:

https://anongit.mindrot.org/openssh.git/commit/?id=1bf477d3cdf1a864646d59820878783d42357a1d

Upstream release notes:

http://www.openssh.com/txt/release-6.9
Comment 1 Vasyl Kaigorodov 2015-07-01 12:59:11 UTC 
Created openssh tracking bugs for this issue:

Affects: fedora-all [bug 1238241]
Comment 2 Fedora Update System 2015-07-10 19:09:17 UTC 
openssh-6.6.1p1-13.fc21 has been pushed to the Fedora 21 stable repository.  If problems still persist, please make note of it in this bug report.
Comment 3 Fedora Update System 2015-07-10 19:18:14 UTC 
openssh-6.9p1-1.fc22 has been pushed to the Fedora 22 stable repository.  If problems still persist, please make note of it in this bug report.
Comment 6 Tomas Hoger 2015-08-04 07:20:09 UTC 
The original reporter published a detailed write-up of this issue.

External References:

https://thejh.net/written-stuff/openssh-6.8-xsecurity
Comment 20 Huzaifa S. Sidhpurwala 2015-10-07 06:53:29 UTC 
Statement:

This issue does not affect the version of openssh package as shipped with Red Hat Enterprise Linux 7. This issue affects the version of openssh package as shipped with Red Hat Enterprise Linux 5 and 6.

Red Hat Product Security has rated this issue as having Moderate security impact. This issue is not currently planned to be addressed in future updates.
Comment 22 Huzaifa S. Sidhpurwala 2015-12-01 07:24:54 UTC 
The version of Xserver (xorg-x11-server) shipped with Red Hat Enterprise Linux 7, disables the XSECURITY extension. Hence this flaw does not affect the version of openssh shipped with Red Hat Enterprise Linux 7.

The above also means that there is no way for openssh to do untrusted/restricted forwarding when X server does not have the XC-SECURITY extension.
Comment 25 errata-xmlrpc 2016-05-10 19:28:52 UTC 
This issue has been addressed in the following products:

  Red Hat Enterprise Linux 6

Via RHSA-2016:0741 https://rhn.redhat.com/errata/RHSA-2016-0741.html
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