CVE-2011-5036 in Rack
Summary
by MITRE
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.
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Analysis
by VulDB Data Team • 08/08/2024
The vulnerability identified as CVE-2011-5036 represents a critical hash collision attack vector affecting the Rack web application framework across multiple versions. This flaw exists in the parameter processing mechanism where the framework computes hash values for form parameters without implementing adequate collision resistance measures. The vulnerability specifically impacts Rack versions prior to 1.1.3, 1.2.x versions before 1.2.5, and 1.3.x versions before 1.3.6, making it a widespread issue affecting numerous web applications built on this framework.
The technical implementation of this vulnerability stems from the hash table implementation within Rack's parameter handling system. When processing form parameters, the framework uses a hash function to store and retrieve key-value pairs, but fails to implement collision-resistant hashing algorithms. Attackers can exploit this weakness by crafting specifically designed form parameters that deliberately cause hash collisions, forcing the system to degrade from optimal O(1) average case performance to O(n) worst-case performance where n represents the number of colliding elements. This degradation results in exponential CPU consumption as the system struggles to resolve hash collisions through linear probing or chaining mechanisms.
From an operational perspective, this vulnerability enables remote attackers to execute effective denial of service attacks against affected systems. The attack requires sending multiple crafted parameters that trigger hash collisions, causing the application server to consume excessive CPU resources and potentially leading to system unresponsiveness or complete service disruption. The impact extends beyond simple resource exhaustion as the vulnerability can be exploited by unauthorized users without requiring authentication, making it particularly dangerous in production environments where availability is critical. The vulnerability aligns with CWE-400, specifically addressing weaknesses in hash table implementation that lead to resource consumption issues, and can be categorized under ATT&CK technique T1499.004 for resource exhaustion attacks.
The mitigation strategy for this vulnerability involves upgrading to patched versions of the Rack framework where the hash collision resistance has been improved. Organizations should prioritize updating their Rack dependencies to versions 1.1.3, 1.2.5, or 1.3.6 respectively, depending on their current version. Additional defensive measures include implementing rate limiting mechanisms for form submissions, monitoring for unusual parameter processing patterns, and configuring application firewalls to detect and block suspicious parameter combinations. Security teams should also consider implementing parameter validation and sanitization routines that can identify and reject potentially malicious parameter sequences before they reach the hash computation layer. The vulnerability demonstrates the importance of cryptographic hash function selection in web frameworks and highlights the need for robust collision resistance mechanisms in all data structures that rely on hash-based lookups.