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DenyHosts Denial of Service and Weakness
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Secunia Advisory:
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SA23236
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Release Date:
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2006-12-06
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Last Update:
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2007-11-01
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Popularity:
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6,313 views
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Critical:
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Moderately critical
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Impact:
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Security Bypass
DoS
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Where:
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From remote
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Solution Status:
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Unpatched
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| Software: | DenyHosts 2.x
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| CVE reference: | CVE-2006-6301
CVE-2007-4323
CVE-2007-5715
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Description:
Tavis Ormandy and Jonathan Underwood have discovered a vulnerability and a weakness in DenyHosts, which can be exploited by malicious people to bypass certain security restrictions or cause a DoS (Denial of Service).
1) An error exists in the parsing of log files before adding an entry in /etc/hosts.deny. This can be exploited to add arbitrary IP addresses to /etc/hosts.deny resulting in a DoS for that IP.
The vulnerability is confirmed in version 2.5 and 2.6. Other versions may also be affected.
2) A weakness exists in the parsing log files containing login attempts blocked by the "AllowUsers" OpenSSH directive. This can be exploited to bypass the logging capability of DenyHosts by trying to login using a user not specifically permited by "AllowUsers".
The weakness is confirmed in version 2.6. Other versions may also be affected.
Solution:
Edit the regular expressions to ensure that log files are parsed properly.
Use another product.
Provided and/or discovered by:
1) Tavis Ormandy
2) Jonathan Underwood
Changelog:
2006-12-08: Added CVE reference.
2007-01-04: Updated "Solution" section.
2007-06-07: Updated "Description" and "Solution" section and "Solution Status" based on information provided by Daniel Cid. Added link to "Original Advisory" section.
2007-08-15: Added CVE reference.
2007-11-01: Added weakness #2 to the advisory.
Original Advisory:
1) http://bugs.gentoo.org/show_bug.cgi?id=157163
http://www.ossec.net/en/attacking-loganalysis.html
2) https://bugzilla.redhat.com/show_bug.cgi?id=237449
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About this Secunia Advisory
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Please note: The information that this Secunia Advisory is based on comes from a third party unless stated otherwise.
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