CVE-2016-6306 in OpenSSL
Summary
by MITRE
The certificate parser in OpenSSL before 1.0.1u and 1.0.2 before 1.0.2i might allow remote attackers to cause a denial of service (out-of-bounds read) via crafted certificate operations, related to s3_clnt.c and s3_srvr.c.
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Analysis
by VulDB Data Team • 09/21/2022
The vulnerability identified as CVE-2016-6306 represents a critical out-of-bounds read flaw within OpenSSL's certificate parsing mechanisms affecting versions prior to 1.0.1u and 1.0.2i. This vulnerability specifically impacts the SSL/TLS implementation during certificate processing operations, creating a potential denial of service condition that can be exploited remotely by attackers. The flaw manifests in the s3_clnt.c and s3_srvr.c source files, which handle client and server side SSL/TLS protocol operations respectively, indicating the issue spans both ends of the secure communication stack.
The technical root cause of this vulnerability stems from inadequate input validation within the certificate parsing routines where OpenSSL fails to properly bounds-check data structures during the processing of X.509 certificates. When a maliciously crafted certificate is presented during the SSL/TLS handshake process, the parser attempts to read memory locations beyond the allocated buffer boundaries, resulting in undefined behavior that typically manifests as application crashes or system instability. This type of vulnerability falls under CWE-129, which specifically addresses insufficient bounds checking, and represents a classic example of memory safety issues that have plagued cryptographic libraries for decades.
The operational impact of CVE-2016-6306 extends beyond simple service disruption as it can be leveraged by remote attackers to perform systematic denial of service attacks against SSL/TLS services. Any system running vulnerable OpenSSL versions that accepts client certificates or processes certificate chains during TLS handshakes becomes a potential target for exploitation. This includes web servers, email servers, database servers, and any network service that relies on OpenSSL for secure communications. The vulnerability is particularly dangerous because it can be triggered without authentication requirements, making it an attractive target for automated scanning and exploitation campaigns that can overwhelm services with repeated denial of service attempts.
Organizations affected by this vulnerability should prioritize immediate patching of all systems running vulnerable OpenSSL versions, as the remediation process involves upgrading to OpenSSL 1.0.1u or 1.0.2i respectively. Security teams should also implement network monitoring to detect potential exploitation attempts, particularly focusing on unusual certificate processing patterns and connection termination behaviors. The ATT&CK framework categorizes this vulnerability under T1499.004 for Network Denial of Service, with the specific technique involving the exploitation of software vulnerabilities to disrupt services. Additionally, system administrators should consider implementing certificate validation policies that limit certificate chain lengths and enforce strict certificate format validation as defensive measures. Organizations should also verify their certificate management processes to ensure that only properly validated certificates are accepted during SSL/TLS handshakes, reducing the attack surface for potential exploitation of similar vulnerabilities in the future.