Rack before 1.1.3, 1.2.x before 1.2.5, and 1.3.x before 1.3.6 computes hash values for form parameters without restricting the ability to trigger hash collisions predictably, which allows remote attackers to cause a denial of service (CPU consumption) by sending many crafted parameters.

Several vulnerabilities were discovered in Rack, a modular Ruby webserver interface. The Common Vulnerabilites and Exposures project identifies the following vulnerabilities :

  - CVE-2011-5036     Rack computes hash values for form parameters without     restricting the ability to trigger hash collisions     predictably, which allows remote attackers to cause a     denial of service (CPU consumption) by sending many     crafted parameters.

  - CVE-2013-0183     A remote attacker could cause a denial of service     (memory consumption and out-of-memory error) via a long     string in a Multipart HTTP packet.

  - CVE-2013-0184     A vulnerability in Rack::Auth::AbstractRequest allows     remote attackers to cause a denial of service via     unknown vectors.

  - CVE-2013-0263     Rack::Session::Cookie allows remote attackers to guess     the session cookie, gain privileges, and execute     arbitrary code via a timing attack involving an HMAC     comparison function that does not run in constant time.

The remote host is affected by the vulnerability described in GLSA-201203-05 (Rack: Denial of Service)

    Rack does not properly randomize hash functions to protect against hash       collision attacks.
  Impact :

    A remote attacker could send a specially crafted form post, possibly       resulting in a Denial of Service condition.
  Workaround :

    There is no known workaround at this time.

Julian Walde and Alexander Klink reported a flaw in the hash function used in the implementation of the Ruby-rack arrays (CVE-2011-5036).
Ruby-rack arrays are implemented using the hash table that maps keys to values. This update fixes the bug.

Note that Tenable Network Security has extracted the preceding description block directly from the Fedora security advisory. Tenable has attempted to automatically clean and format it as much as possible without introducing additional issues.

oCERT reports :

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.

ID	Name	Product	Family	Severity
70534	Debian DSA-2783-1 : librack-ruby - several vulnerabilities	Nessus	Debian Local Security Checks	medium
58215	GLSA-201203-05 : Rack: Denial of Service	Nessus	Gentoo Local Security Checks	medium
57564	Fedora 15 : rubygem-rack-1.1.0-4.fc15 (2012-0233)	Nessus	Fedora Local Security Checks	medium
57563	Fedora 16 : rubygem-rack-1.3.0-2.fc16 (2012-0166)	Nessus	Fedora Local Security Checks	medium
57552	FreeBSD : Multiple implementations -- DoS via hash algorithm collision (91be81e7-3fea-11e1-afc7-2c4138874f7d)	Nessus	FreeBSD Local Security Checks	high

Detections

Analytics

CVE-2011-5036

high

Tenable Plugins

medium

medium

medium

medium

high