CVE-2012-6702 in iTunes
Summary
by MITRE
Expat, when used in a parser that has not called XML_SetHashSalt or passed it a seed of 0, makes it easier for context-dependent attackers to defeat cryptographic protection mechanisms via vectors involving use of the srand function.
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Analysis
by VulDB Data Team • 08/23/2020
The vulnerability identified as CVE-2012-6702 affects the Expat XML parser library, a widely used open source component for parsing XML data in numerous applications and systems. This weakness specifically relates to the parser's handling of hash table collisions and its interaction with random number generation mechanisms. The flaw exists when applications fail to properly initialize the hash salt mechanism within Expat, creating predictable hash values that can be exploited by malicious actors. The vulnerability represents a significant concern for cryptographic systems that rely on hash functions for security purposes, as it undermines the randomness and unpredictability that cryptographic protections depend upon.
The technical root cause of this vulnerability stems from the Expat library's default behavior when no explicit hash salt is provided during parser initialization. When XML_SetHashSalt is not called or is called with a seed value of zero, the parser defaults to using a predictable sequence based on the srand function for seeding hash tables. This predictable seeding allows attackers to calculate and manipulate hash values, effectively enabling them to craft malicious XML inputs that exploit hash collision vulnerabilities. The flaw operates at the level of hash table implementation within the XML parser, where collision resistance is crucial for maintaining system integrity and preventing denial of service attacks. This weakness directly maps to CWE-327, which addresses the use of insecure random number generators in cryptographic contexts, and aligns with ATT&CK technique T1211 for exploiting weaknesses in cryptographic implementations.
The operational impact of CVE-2012-6702 extends beyond simple denial of service scenarios to potentially enable more sophisticated attacks against systems relying on Expat for XML processing. Context-dependent attackers can leverage this vulnerability to perform hash collision attacks that consume excessive CPU resources, leading to resource exhaustion and service disruption. Additionally, the predictable nature of hash values can be exploited in more advanced scenarios such as cache poisoning attacks or attacks targeting cryptographic systems that depend on hash functions for integrity verification. The vulnerability affects numerous applications including web servers, application frameworks, and security tools that utilize Expat for XML parsing, making it particularly dangerous given the widespread adoption of this library. Organizations running systems with vulnerable Expat versions face potential exploitation risks that could lead to system compromise or denial of service conditions.
Mitigation strategies for CVE-2012-6702 require immediate attention from system administrators and developers who utilize Expat in their applications. The primary remediation involves ensuring that XML_SetHashSalt is properly called with a sufficiently random seed value during parser initialization, typically using a cryptographically secure random number generator. Applications should implement proper initialization routines that explicitly set hash salt values to prevent the default behavior that leads to predictable hash sequences. System administrators should conduct thorough vulnerability assessments to identify all applications using Expat and verify proper implementation of hash salt mechanisms. Updates to Expat library versions that address this issue should be prioritized, and organizations should consider implementing monitoring solutions to detect potential exploitation attempts. The vulnerability also highlights the importance of proper input validation and sanitization in XML processing systems, as attackers may attempt to exploit various aspects of XML parsing to bypass security controls. Security teams should also consider implementing network-based detection measures to identify suspicious XML processing patterns that could indicate exploitation attempts.