CVE-2011-4838 in JRuby
Summary
by MITRE
JRuby before 1.6.5.1 computes hash values without 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.
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Analysis
by VulDB Data Team • 12/03/2024
The vulnerability described in CVE-2011-4838 represents a significant security flaw in JRuby versions prior to 1.6.5.1 that affects the implementation of hash table operations within the Ruby interpreter. This issue stems from the insufficient design of the hash function implementation, which fails to properly limit the conditions under which hash collisions can be deliberately triggered by malicious actors. The vulnerability specifically targets the hash table data structure that is fundamental to many applications, particularly those relying on hash-based lookups for performance optimization. Attackers can exploit this weakness by crafting specific input data that forces the hash table to experience predictable collision patterns, thereby consuming excessive CPU resources and leading to system performance degradation or complete service unavailability.
The technical root cause of this vulnerability lies in the hash function's susceptibility to predictable collision attacks, which is classified under CWE-327 in the Common Weakness Enumeration catalog. This weakness represents a failure in cryptographic implementation where the hash algorithm does not adequately resist adversarial input that can be crafted to produce collisions. The vulnerability manifests when applications using JRuby maintain hash tables for data storage and retrieval operations, particularly in scenarios involving user-controlled input processing. The flaw enables attackers to construct input that will consistently map to the same hash bucket, forcing the hash table implementation to degrade from optimal O(1) lookup time to O(n) performance, where n represents the number of collisions. This degradation occurs because hash tables typically resolve collisions through chaining or open addressing, and when collisions are predictable and frequent, the entire system becomes vulnerable to resource exhaustion attacks.
The operational impact of CVE-2011-4838 extends beyond simple performance degradation to represent a serious denial of service threat that can affect any application running on vulnerable JRuby implementations. When exploited, this vulnerability allows context-dependent attackers to consume excessive CPU cycles, potentially leading to complete system unresponsiveness or application crashes. The attack vector is particularly concerning because it can be executed without requiring elevated privileges or specialized knowledge of the underlying system architecture. Applications that process user input through hash-based data structures, such as web applications handling form submissions, API endpoints processing JSON data, or any system maintaining hash tables for caching or lookup operations, become vulnerable to this attack. The vulnerability is particularly dangerous in high-traffic environments where a single malicious request could cause cascading failures across multiple application instances.
Mitigation strategies for CVE-2011-4838 focus primarily on upgrading to JRuby version 1.6.5.1 or later, which includes the necessary fixes to prevent predictable hash collisions. Organizations should conduct thorough vulnerability assessments to identify all systems running vulnerable JRuby versions and prioritize patching efforts accordingly. Additionally, implementing input validation and sanitization measures can provide defense-in-depth protection by limiting the ability of malicious actors to craft specifically designed inputs that trigger hash collisions. System administrators should also consider implementing rate limiting and resource monitoring to detect unusual CPU consumption patterns that may indicate exploitation attempts. From an operational security perspective, this vulnerability aligns with ATT&CK technique T1499.001 which describes resource exhaustion attacks, and represents a classic example of how weaknesses in fundamental data structures can be exploited to achieve denial of service outcomes. The vulnerability demonstrates the importance of proper hash function design and the need for cryptographic implementations that resist adversarial input manipulation, as outlined in industry best practices for secure coding and system design.