CVE-2012-5371 in Ruby
Summary
by MITRE
Ruby (aka CRuby) 1.9 before 1.9.3-p327 and 2.0 before r37575 computes hash values without properly restricting the ability to trigger hash collisions predictably, which allows context-dependent attackers to cause a denial of service (CPU consumption) via crafted input to an application that maintains a hash table, as demonstrated by a universal multicollision attack against a variant of the MurmurHash2 algorithm, a different vulnerability than CVE-2011-4815.
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Analysis
by VulDB Data Team • 12/20/2021
The vulnerability identified as CVE-2012-5371 represents a critical hash collision weakness in Ruby's implementation that affects versions prior to 1.9.3-p327 and 2.0 r37575. This flaw stems from Ruby's hash table implementation failing to properly restrict the conditions under which hash collisions can be triggered predictably. The vulnerability specifically targets the hash computation algorithm used by Ruby's hash table data structure, creating a scenario where attackers can craft input data that will consistently produce hash collisions. This issue is particularly dangerous because it enables attackers to exploit the fundamental hash table mechanism that Ruby applications rely upon for efficient data storage and retrieval operations.
The technical implementation of this vulnerability leverages a universal multicollision attack against a variant of the MurmurHash2 algorithm, demonstrating how predictable hash collisions can be generated through carefully constructed input sequences. When Ruby applications process such malicious input, the hash table's performance degrades dramatically as collision resolution becomes increasingly complex, leading to exponential CPU consumption. The attack exploits the fact that Ruby's hash function does not adequately randomize hash values when processing specific input patterns, allowing attackers to craft inputs that will consistently hash to the same value or nearby values in the hash table. This predictable collision behavior is distinct from other hash-related vulnerabilities such as CVE-2011-4815, which targeted different aspects of hash computation.
The operational impact of CVE-2012-5371 manifests as a significant denial of service condition where Ruby applications become unresponsive or extremely slow when processing malicious input. Attackers can cause substantial CPU resource consumption by submitting specially crafted data that forces the hash table to experience maximum collision rates, effectively turning what should be O(1) average time complexity operations into O(n) or worse performance scenarios. This vulnerability affects any Ruby application that utilizes hash tables for data storage, including web applications, database systems, and any software that relies on hash-based data structures for efficient lookups. The attack can be particularly devastating in web applications where user input is processed through hash tables, as it can be exploited to consume server resources and potentially cause application crashes or service interruptions that affect legitimate users.
Organizations should implement immediate mitigations including upgrading to Ruby versions 1.9.3-p327 or later, or Ruby 2.0 r37575 and newer, which contain fixes for this vulnerability. Additionally, developers should consider implementing input validation and sanitization measures to detect and reject potentially malicious hash input patterns before they can be processed by hash tables. The vulnerability aligns with CWE-327, which addresses weak cryptographic algorithms and hash functions, and maps to ATT&CK technique T1499.004 for network denial of service attacks. Security teams should also monitor for potential exploitation attempts through unusual CPU usage patterns or hash table performance degradation that may indicate an active attack targeting this vulnerability.