CVE-2016-6891 in MatrixSSL
Summary
by MITRE
MatrixSSL before 3.8.6 allows remote attackers to cause a denial of service (out-of-bounds read) via a crafted ASN.1 Bit Field primitive in an X.509 certificate.
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Analysis
by VulDB Data Team • 11/12/2024
The vulnerability identified as CVE-2016-6891 represents a critical out-of-bounds read flaw within MatrixSSL library versions prior to 3.8.6. This issue specifically manifests when processing ASN.1 Bit Field primitives contained within X.509 certificates, creating a remote denial of service condition that can be exploited by attackers without authentication. The vulnerability resides in the certificate parsing logic where the library fails to properly validate the length of bit field primitives, leading to memory access violations when processing malformed certificate data. Such flaws typically originate from inadequate input validation mechanisms that do not account for edge cases in ASN.1 encoding structures, particularly when dealing with variable-length bit strings that may exceed expected boundaries.
The technical implementation of this vulnerability stems from improper bounds checking during ASN.1 parsing operations within the MatrixSSL implementation. When an X.509 certificate containing a malformed bit field primitive is processed, the library attempts to read memory locations beyond the allocated buffer boundaries, resulting in unpredictable behavior and system instability. This type of vulnerability falls under CWE-129, which specifically addresses insufficient bounds checking, and represents a classic example of how improper input validation can lead to memory corruption issues. The attack vector requires only that a malicious certificate be presented to a system using the vulnerable MatrixSSL library, making it particularly dangerous in scenarios where certificate validation occurs automatically during TLS handshakes or certificate chain processing.
From an operational impact perspective, this vulnerability can result in complete system downtime or application crashes across any service utilizing the affected MatrixSSL library version. The denial of service condition affects not only the immediate target but can potentially cascade through interconnected systems that rely on secure communication channels. Attackers can exploit this vulnerability to disrupt services by presenting crafted certificates that trigger the out-of-bounds read condition, effectively rendering the targeted system unavailable to legitimate users. This vulnerability particularly impacts web servers, email servers, and any infrastructure component that processes X.509 certificates for authentication or encryption purposes, making it a significant concern for enterprise security operations and compliance requirements.
The remediation strategy for CVE-2016-6891 involves immediate upgrading to MatrixSSL version 3.8.6 or later, which includes proper bounds checking mechanisms for ASN.1 bit field parsing. Organizations should conduct comprehensive inventory assessments to identify all systems utilizing vulnerable MatrixSSL versions and prioritize patching activities accordingly. Security teams should also implement network monitoring to detect potential exploitation attempts and establish incident response procedures for handling denial of service events. Additional mitigations include certificate validation hardening, implementing certificate pinning where appropriate, and maintaining up-to-date security patches across all cryptographic libraries. This vulnerability demonstrates the importance of robust input validation in cryptographic implementations and aligns with ATT&CK technique T1499.004, which covers network denial of service attacks, highlighting the need for comprehensive security controls that address both application-level and network-level threats.