Bug 164661 - CVE-2003-0386 host based access bypass
CVE-2003-0386 host based access bypass
Product: Red Hat Enterprise Linux 3
Classification: Red Hat
Component: openssh (Show other bugs)
All Linux
medium Severity low
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Assigned To: Tomas Mraz
Brian Brock
: Security
Depends On:
Blocks: RHEL3U8CanFix
  Show dependency treegraph
Reported: 2005-07-29 15:29 EDT by Paul Waterman
Modified: 2007-11-30 17:07 EST (History)
2 users (show)

See Also:
Fixed In Version: RHSA-2006-0298
Doc Type: Bug Fix
Doc Text:
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Clone Of:
Last Closed: 2006-07-20 08:53:13 EDT
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RHEL 7.3 requirements from Atomic Host:
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Description Paul Waterman 2005-07-29 15:29:21 EDT
From Bugzilla Helper:
User-Agent: Mozilla/5.0 (Windows; U; Windows NT 5.0; en-US; rv:1.7.7) Gecko/20050414

Description of problem:
The OpenSSH server included with RHEL 3.0 (apparently all updates) is vulnerable to CAN-2003-0386. Apparently the fix for this vulnerability has never been backported into Red Hat's openssh-server-3.6.1p2 RPMs.

An attacker can bypass IP-based AllowUser restrictions in the /etc/ssh/sshd_config file if the attacker controls reverse DNS for his system by providing a reverse DNS hostname for his machine which is the IP address allowed by the AllowUser restriction.

This vulnerability can be mitigated by turning on VerifyReverseMapping, but this is turned off by default.

Version-Release number of selected component (if applicable):

How reproducible:

Steps to Reproduce:
1. Add an AllowUser restriction to /etc/ssh/sshd_config. 

AllowUser *@

2. Restart sshd.

% service sshd restart

3. Set up reverse DNS to return the allowed IP address for a different machine.    

% host domain name pointer

4. From the remote host which should be disallowed, ssh to the vulnerable host.

Actual Results:  Login is allowed via ssh.

Expected Results:  The user should receive a "permission denied" message and the login should be disallowed.

Additional info:
Comment 1 Mark J. Cox (Product Security) 2005-08-01 10:58:11 EDT
Note: At the time of announcement the official response was:  "If you depend on
IP or DNS based access control, make sure VerifyReverseMapping is turned on in
your sshd_config file."

Comment 2 Tomas Mraz 2005-08-01 11:26:57 EDT
I've backported a patch from openssh-3.9p1.
Comment 9 Bob Johnson 2006-04-11 12:07:37 EDT
This issue is on Red Hat Engineering's list of planned work items 
for the upcoming Red Hat Enterprise Linux 3.8 release.  Engineering 
resources have been assigned and barring unforeseen circumstances, Red 
Hat intends to include this item in the 3.8 release.
Comment 13 Red Hat Bugzilla 2006-07-20 08:53:13 EDT
An advisory has been issued which should help the problem
described in this bug report. This report is therefore being
closed with a resolution of ERRATA. For more information
on the solution and/or where to find the updated files,
please follow the link below. You may reopen this bug report
if the solution does not work for you.


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