CVE-2012-5370 in JRuby
Summary
by MITRE
JRuby 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 the MurmurHash2 algorithm, a different vulnerability than CVE-2011-4838.
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Analysis
by VulDB Data Team • 12/20/2021
The vulnerability described in CVE-2012-5370 represents a significant weakness in JRuby's hash table implementation that enables attackers to exploit hash collision vulnerabilities for denial of service attacks. This issue specifically affects the MurmurHash2 algorithm used by JRuby, creating conditions where malicious input can be crafted to generate predictable hash collisions that degrade system performance. The vulnerability operates at the fundamental level of hash table operations, where the collision handling mechanism fails to properly restrict input that could lead to predictable collision patterns, making it particularly dangerous in applications that rely heavily on hash-based data structures.
The technical flaw stems from JRuby's inadequate handling of hash value computation during collision resolution, allowing attackers to craft input specifically designed to trigger hash collisions in the MurmurHash2 algorithm. This vulnerability enables what is known as a universal multicollision attack, where multiple inputs can be generated that map to the same hash value, causing hash tables to degenerate into linked lists or other inefficient data structures. The impact is particularly severe because hash tables are fundamental data structures used throughout applications for fast data retrieval, and when they become inefficient, CPU resources are consumed excessively as the system must process collision chains rather than perform constant-time lookups.
From an operational perspective, this vulnerability creates a context-dependent attack vector that can be exploited when applications using JRuby maintain hash tables containing user-controlled data. The attack requires minimal privileges and can be executed against any JRuby application that processes untrusted input through hash-based operations. The CPU consumption becomes exponential as the hash table degrades from O(1) to O(n) lookup times, potentially leading to complete system unresponsiveness or resource exhaustion. This vulnerability specifically differs from CVE-2011-4838, which addressed a different hash collision issue, making CVE-2012-5370 a distinct but related threat that affects the same underlying algorithmic weakness in different contexts.
The attack methodology relies on understanding hash table collision patterns and the specific characteristics of MurmurHash2's output distribution. Attackers can construct inputs that force hash table entries to collide predictably, causing the system to spend excessive CPU cycles processing collision chains. This vulnerability aligns with CWE-400, which addresses Uncontrolled Resource Consumption, and maps to ATT&CK technique T1499.004 for Resource Exhaustion, specifically targeting the system's computational resources through hash table manipulation. The exploitation requires knowledge of the hash algorithm implementation and the ability to craft inputs that will produce the desired collision behavior, making it a sophisticated but achievable attack against vulnerable JRuby applications.
Mitigation strategies include implementing hash function randomization or using alternative hash algorithms that are resistant to collision attacks, upgrading to JRuby versions that address this specific vulnerability, and applying input validation techniques to limit the potential for malicious hash collision inputs. Organizations should also consider implementing rate limiting and resource monitoring to detect and prevent abuse of this vulnerability. The fix typically involves modifying the hash table implementation to prevent predictable collision patterns and ensure that hash values are computed in a way that maintains efficient lookup times regardless of input characteristics, thereby addressing the core issue identified in this CVE and protecting against similar hash collision attacks that could compromise system availability.