CVE-2012-1150 in Mac OS X
Summary
by MITRE
Python before 2.6.8, 2.7.x before 2.7.3, 3.x before 3.1.5, and 3.2.x before 3.2.3 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 • 06/01/2021
This vulnerability represents a critical weakness in Python's hash table implementation that enables attackers to perform denial of service attacks through predictable hash collisions. The flaw exists in multiple Python versions including 2.x series before 2.6.8, 2.7.x before 2.7.3, 3.x before 3.1.5, and 3.2.x before 3.2.3, making it a widespread issue affecting a significant portion of Python deployments. The vulnerability stems from the hash function's inability to properly limit collision probability, allowing malicious actors to craft specific inputs that deliberately trigger hash table collisions. This weakness is categorized under CWE-400 as unspecified vulnerability in hash table implementation and aligns with ATT&CK technique T1499.100 for resource exhaustion attacks through hash collision exploitation.
The technical implementation of this vulnerability exploits the fundamental design of Python's hash table data structure where objects are stored and retrieved using hash values. When an attacker provides carefully constructed input data, they can manipulate the hash computation to force multiple objects into the same hash bucket, creating a degenerate hash table performance scenario. This degradation transforms what should be O(1) average time complexity for hash table operations into O(n) worst-case complexity, where n represents the number of collisions. The impact is particularly severe because hash tables are extensively used throughout Python applications, including dictionary operations, set membership testing, and various data structures that rely on hash-based storage mechanisms.
The operational impact of CVE-2012-1150 manifests as significant CPU consumption and potential application hang or crash scenarios. Attackers can exploit this vulnerability by submitting specially crafted data that causes hash table lookups to degrade from constant time to linear time complexity, effectively creating a resource exhaustion attack. This makes the vulnerability particularly dangerous in web applications, network services, and any system that processes untrusted input through hash-based data structures. The vulnerability is context-dependent, meaning it requires an application that actually uses hash tables and processes user-provided input, but given Python's widespread adoption, many applications are potentially affected. The attack vector typically involves sending malicious input to services that use Python dictionaries or hash-based collections, leading to substantial CPU utilization and service disruption.
Mitigation strategies for this vulnerability involve upgrading to patched Python versions where the hash function implementation has been improved to prevent predictable collision attacks. The most effective solution is to update to Python 2.6.8, 2.7.3, 3.1.5, or 3.2.3 respectively, which contain improved hash algorithms that resist collision attacks. Organizations should also implement input validation and sanitization measures to reduce the attack surface, though this is not a complete solution. Additional defensive measures include monitoring for unusual CPU consumption patterns, implementing rate limiting for input processing, and considering alternative data structures where hash tables are not essential. The vulnerability highlights the importance of secure hash function design and demonstrates how seemingly minor implementation details can lead to significant security implications in widely-used programming languages.