CVE-2011-4815 in Ruby
Summary
by MITRE
Ruby (aka CRuby) before 1.8.7-p357 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 identified as CVE-2011-4815 represents a critical hash collision attack vector affecting Ruby implementations prior to version 1.8.7-p357. This weakness stems from the insecure computation of hash values within the Ruby interpreter, specifically in the hash table implementation that underpins many data structures and operations within Ruby applications. The vulnerability is classified under CWE-327, which deals with the use of a broken or weak cryptographic algorithm, and more specifically relates to weaknesses in hash function implementations that fail to provide adequate resistance against collision attacks.
The technical flaw manifests in Ruby's hash table construction process where the hash computation algorithm does not adequately restrict the ability to generate predictable hash collisions. Attackers can craft specific input data that will deliberately create hash collisions within Ruby applications that rely heavily on hash tables for data storage and retrieval operations. This vulnerability operates at the application level and can be exploited by context-dependent attackers who understand the target application's data handling patterns. The attack vector specifically targets applications that maintain hash tables, which is a common pattern across numerous Ruby applications including web frameworks, database systems, and general purpose applications that utilize hash-based data structures.
The operational impact of this vulnerability is significant as it enables attackers to cause a denial of service condition through excessive cpu consumption. When an attacker successfully triggers hash collisions, the hash table performance degrades from optimal O(1) lookup time to O(n) in worst-case scenarios, where n represents the number of colliding elements. This degradation can be exploited to consume excessive system resources and potentially cause application crashes or system unresponsiveness. The vulnerability affects Ruby implementations that use the default hash function, which is commonly employed across various Ruby applications and frameworks, making it a widespread concern for systems running vulnerable versions of the interpreter.
Mitigation strategies for CVE-2011-4815 include immediate upgrading to Ruby version 1.8.7-p357 or later, which contains the necessary fixes to prevent predictable hash collisions. Organizations should also implement input validation and sanitization measures to detect and reject suspicious input patterns that may be designed to trigger hash collisions. Additionally, application developers should consider implementing hash table size limits and collision handling mechanisms that can detect and respond to abnormal collision patterns. The vulnerability aligns with ATT&CK technique T1499.004, which covers network denial of service attacks, and represents a classic example of a resource exhaustion attack that can be classified under the broader category of DoS vulnerabilities. System administrators should monitor application performance and implement intrusion detection systems that can identify unusual hash table behavior patterns that may indicate exploitation attempts.