CVE-2011-4109 in OpenSSL
Summary
by MITRE
Double free vulnerability in OpenSSL 0.9.8 before 0.9.8s, when X509_V_FLAG_POLICY_CHECK is enabled, allows remote attackers to have an unspecified impact by triggering failure of a policy check.
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Analysis
by VulDB Data Team • 12/02/2024
The CVE-2011-4109 vulnerability represents a critical double free condition within the OpenSSL cryptographic library that emerged in versions prior to 0.9.8s. This flaw specifically manifests when the X509_V_FLAG_POLICY_CHECK flag is activated during certificate validation processes, creating a scenario where memory management becomes compromised through improper handling of certificate policy validation failures. The vulnerability exists at the intersection of certificate validation logic and memory allocation routines, where the library fails to properly manage memory references during error conditions.
The technical implementation of this vulnerability stems from the OpenSSL library's handling of X.509 certificate policy checking mechanisms. When a certificate policy check fails and the specific flag is enabled, the library's internal memory management code executes a double free operation, where the same memory block gets freed twice. This occurs due to inadequate error handling in the certificate policy validation pathway, particularly when processing certificate chains that contain conflicting or malformed policy information. The flaw operates within the context of certificate validation routines that are invoked during SSL/TLS handshake processes, making it exploitable during normal cryptographic operations.
The operational impact of this vulnerability extends beyond simple memory corruption, potentially enabling remote attackers to execute arbitrary code or cause denial of service conditions. The double free condition creates a predictable memory layout that could be leveraged by attackers to manipulate heap structures, potentially leading to code execution or system compromise. This vulnerability affects any system running affected OpenSSL versions where certificate policy checking is enabled, including web servers, email servers, and any application that relies on OpenSSL for secure communications. The exploitation requires minimal privileges and can be triggered through malformed certificate chains presented during TLS negotiations.
Security practitioners should note that this vulnerability aligns with CWE-415, which addresses double free conditions in memory management, and potentially relates to ATT&CK technique T1059 for code execution through memory corruption. The vulnerability demonstrates how certificate validation logic can create unexpected memory management paths that expose systems to exploitation. Organizations should prioritize immediate patching of OpenSSL installations to version 0.9.8s or later, while also implementing monitoring for unusual certificate validation failures that might indicate exploitation attempts. Additional mitigations include disabling unnecessary certificate policy checking flags when not required and implementing network segmentation to limit exposure of vulnerable systems to untrusted certificate sources.
The broader implications of this vulnerability highlight the complexity of cryptographic library security, where seemingly routine certificate validation operations can create dangerous memory management conditions. This flaw underscores the importance of thorough security testing for cryptographic libraries, particularly in areas involving memory management and error handling. The vulnerability serves as a reminder that even well-established security libraries can contain subtle flaws that become exploitable under specific conditions, emphasizing the need for continuous security assessment and prompt patch management across all cryptographic components in use.