CVE-2012-6109 in rack
Summary
by MITRE
lib/rack/multipart.rb in Rack before 1.1.4, 1.2.x before 1.2.6, 1.3.x before 1.3.7, and 1.4.x before 1.4.2 uses an incorrect regular expression, which allows remote attackers to cause a denial of service (infinite loop) via a crafted Content-Disposion header.
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Analysis
by VulDB Data Team • 12/29/2021
The vulnerability described in CVE-2012-6109 represents a critical denial of service flaw within the Rack web application framework that affected multiple versions prior to specific security patches. This issue resides in the lib/rack/multipart.rb file where the framework processes multipart form data commonly used in web applications for file uploads and form submissions. The vulnerability stems from an improperly constructed regular expression that fails to handle certain malformed input patterns correctly, creating a scenario where malicious actors can exploit this weakness to disrupt service availability.
The technical implementation of this vulnerability involves the use of a flawed regular expression pattern within Rack's multipart parsing logic that processes the Content-Disposition header field. When a specially crafted Content-Disposition header is received by the application, the regular expression enters an infinite loop during pattern matching operations, consuming excessive CPU resources and preventing the server from processing legitimate requests. This behavior constitutes a classic denial of service attack vector where the attacker can cause the application to become unresponsive or crash entirely. The vulnerability is particularly dangerous because it can be triggered through standard HTTP requests without requiring authentication or special privileges, making it accessible to any remote attacker who can send HTTP traffic to the affected server.
From an operational impact perspective, this vulnerability presents significant risk to web applications built on the Rack framework, which powers numerous Ruby-based web applications including popular frameworks like Ruby on Rails. The infinite loop condition created by the faulty regular expression can cause the application server to become unresponsive, leading to complete service disruption for users attempting to access the affected application. The attack requires minimal effort to execute and can be performed at scale, potentially causing widespread service degradation across multiple applications. Organizations running vulnerable versions of Rack could experience extended downtime, loss of user access, and potential revenue impact depending on the criticality of their services.
Security mitigations for this vulnerability involve upgrading to patched versions of the Rack framework where the regular expression has been corrected to properly handle all valid and invalid input patterns. The specific patched versions include Rack 1.1.4, 1.2.6, 1.3.7, and 1.4.2, respectively, which contain the necessary corrections to prevent the infinite loop condition. Additionally, organizations should implement proper input validation and sanitization measures at the application level to reduce the attack surface, though the primary fix must occur at the framework level. Network-level protections such as rate limiting and request filtering can provide additional defense in depth, though these measures are secondary to the core framework patching approach. This vulnerability aligns with CWE-1217 which addresses improper handling of regular expressions and demonstrates characteristics consistent with attack patterns found in the MITRE ATT&CK framework under the privilege escalation and denial of service categories, specifically targeting the application layer of web infrastructure.