#2011-003 multiple implementations denial-of-service via hash algorithm
collision

Description:

A variety of programming languages suffer from a denial-of-service (DoS)
condition against storage functions of key/value pairs in hash data
structures, the condition can be leveraged by exploiting predictable
collisions in the underlying hashing algorithms.

The issue finds particular exposure in web server applications and/or
frameworks. In particular, the lack of sufficient limits for the number of
parameters in POST requests in conjunction with the predictable collision
properties in the hashing functions of the underlying languages can render web
applications vulnerable to the DoS condition. The attacker, using specially
crafted HTTP requests, can lead to a 100% of CPU usage which can last up to
several hours depending on the targeted application and server performance,
the amplification effect is considerable and requires little bandwidth and
time on the attacker side.

The condition for predictable collisions in the hashing functions has been
reported for the following language implementations: Java, JRuby, PHP, Python,
Rubinius, Ruby. In the case of the Ruby language, the 1.9.x branch is not
affected by the predictable collision condition since this version includes a
randomization of the hashing function.

The vulnerability outlined in this advisory is practically identical to the
one reported in 2003 and described in the paper Denial of Service via
Algorithmic Complexity Attacks which affected the Perl language.

The reporters own advisory can be found at
http://www.nruns.com/_downloads/advisory28122011.pdf

Affected version:
Java, all versions
JRuby <= 1.6.5
PHP <= 5.3.8, <= 5.4.0RC3
Python, all versions
Rubinius, all versions
Ruby <= 1.8.7-p356

Apache Geronimo, all versions
Apache Tomcat <= 5.5.34, <= 6.0.34, <= 7.0.22
Oracle Glassfish <= 3.1.1
Jetty, all versions
Plone, all versions
Rack, all versions
V8 JavaScript Engine, all versions

Fixed version:
Java, N/A
JRuby >= 1.6.5.1
PHP >= 5.3.9, >= 5.4.0RC4
Python, N/A
Rubinius, N/A
Ruby >= 1.8.7-p357, 1.9.x

Apache Geronimo, N/A
Apache Tomcat >= 5.5.35, >= 6.0.35, >= 7.0.23
Oracle Glassfish, N/A (Oracle reports that the issue is fixed in the main codeline and scheduled for a future CPU)
Jetty, N/A
Plone, N/A
Rack, N/A
V8 JavaScript Engine, N/A

Credit: vulnerability report and PoC code received from Alexander Klink
<alexander.klink AT nruns.com> and Julian Waelde <jwaelde AT
cdc.informatik.tu-darmstadt.de>.

CVE: CVE-2011-4461 (Jetty), CVE-2011-4838 (JRuby), CVE-2011-4885 (PHP),
     CVE-2011-4462 (Plone), CVE-2011-4815 (Ruby)

Timeline:

2011-09-25: vulnerability report received, reporters set embargo date to December 27th
2011-10-18: contacted maintainers of Apache Tomcat, Apache Geronimo, Jetty, Java, Plone, Zope, V8
2011-11-01: contacted maintainers of Ruby on Rails, Ruby, Python, PHP
2011-11-01: contacted affected distributions
2011-11-02: contacted JRuby maintainer
2011-12-13: contacted Ruby Installer maintainer
2011-12-14: assigned CVE for Ruby
2011-12-15: assigned CVE for JRuby
2011-12-13: contacted Rack maintainer
2011-12-16: assigned CVE for Apache Tomcat
2011-12-21: assigned CVE for PHP
2011-12-28: advisory release

References:
http://www.nruns.com/_downloads/advisory28122011.pdf
http://www.cs.rice.edu/~scrosby/hash/CrosbyWallach_UsenixSec2003.pdf
http://svn.php.net/viewvc?view=revision&revision=321003 (unstable, not final)
http://svn.php.net/viewvc?view=revision&revision=321040 (unstable, not final)
https://gist.github.com/52bbc6b9cc19ce330829

Permalink:
http://www.ocert.org/advisories/ocert-2011-003.html

-- 
Andrea Barisani |                Founder & Project Coordinator
          oCERT | OSS Computer Security Incident Response Team

<lcars@ocert.org>                         http://www.ocert.org
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        "Pluralitas non est ponenda sine necessitate"