Red Hat Bugzilla – Bug 164661
CVE-2003-0386 host based access bypass
Last modified: 2007-11-30 17:07:08 EST
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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):
Steps to Reproduce:
1. Add an AllowUser restriction to /etc/ssh/sshd_config.
2. Restart sshd.
% service sshd restart
3. Set up reverse DNS to return the allowed IP address for a different machine.
% host 192.168.0.40
184.108.40.206.in-addr.arpa domain name pointer 192.168.0.20.
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.
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."
I've backported a patch from openssh-3.9p1.
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.
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.