CVE-2012-0839 in OCaml
Summary
by MITRE
OCaml 3.12.1 and earlier 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 • 03/04/2025
The vulnerability identified as CVE-2012-0839 affects OCaml versions 3.12.1 and earlier, presenting a significant security concern related to hash table implementation. This flaw stems from the programming language's hash function design which fails to adequately restrict hash collision possibilities, creating predictable conditions that adversaries can exploit. The vulnerability specifically targets applications that utilize hash tables as their primary data structure for storing and retrieving information, making it particularly dangerous in systems where hash table operations are frequent and performance-critical.
The technical root cause of this vulnerability lies in the hash computation algorithm used by OCaml's runtime system. When applications process user input through hash tables, the flawed hash function allows attackers to craft specific inputs that deliberately trigger hash collisions. This occurs because the hash function does not implement sufficient entropy or randomization mechanisms to prevent attackers from determining input values that will map to the same hash bucket. The vulnerability is classified under CWE-327, which deals with use of a broken or weak cryptographic algorithm, though in this case the weakness manifests in the hash function rather than traditional cryptographic operations. The predictable nature of these collisions means that an attacker can systematically construct input data that will cause hash table operations to degrade from optimal O(1) time complexity to O(n) worst-case performance, where n represents the number of elements in the hash table.
The operational impact of this vulnerability extends beyond simple performance degradation to constitute a full denial of service condition. When an attacker successfully triggers predictable hash collisions, the hash table operations become computationally expensive, consuming excessive CPU resources and potentially causing applications to become unresponsive or crash entirely. This type of attack is particularly insidious because it can be executed with relatively simple input crafting techniques and requires minimal computational resources from the attacker. The vulnerability affects any application built with OCaml 3.12.1 or earlier that processes external input through hash tables, including web applications, database systems, and network services. The attack vector is context-dependent, meaning that the vulnerability only manifests when applications process user-controlled input through hash-based data structures, making it difficult to detect without proper application monitoring and input validation measures.
Mitigation strategies for CVE-2012-0839 primarily focus on upgrading to newer versions of OCaml where the hash function has been improved to prevent predictable collisions. The recommended approach involves immediate migration to OCaml versions 3.12.2 or later, which contain fixed hash computation algorithms that provide better resistance against collision attacks. Additionally, applications should implement input validation and sanitization measures to reduce the attack surface, including limiting input length and character sets that can be processed through hash tables. Organizations should also consider implementing rate limiting and resource monitoring to detect unusual CPU consumption patterns that might indicate exploitation attempts. From a defensive standpoint, this vulnerability aligns with ATT&CK technique T1499.004, which covers network denial of service attacks, and represents a specific implementation weakness that can be addressed through proper software maintenance and security patching procedures. The vulnerability demonstrates the importance of cryptographic and hashing algorithm design in security-critical applications, emphasizing that even fundamental language features can present significant attack vectors when not properly secured against adversarial input manipulation.