CVE-2016-5285 in NSS
Summary
by MITRE
Null pointer dereference vulnerability exists in K11_SignWithSymKey / ssl3_ComputeRecordMACConstantTime in NSS before 3.26, which causes the TLS/SSL server using NSS to crash.
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Analysis
by VulDB Data Team • 09/27/2024
The vulnerability identified as CVE-2016-5285 represents a critical null pointer dereference flaw within the Network Security Services (NSS) library, specifically affecting the K11_SignWithSymKey and ssl3_ComputeRecordMACConstantTime functions. This issue resides in the cryptographic processing components of NSS, which is widely utilized by web browsers, email clients, and other security applications for implementing TLS/SSL protocols. The vulnerability manifests when an NSS-based TLS/SSL server processes certain malformed cryptographic operations, leading to a crash condition that can be exploited to cause denial of service attacks. The flaw affects all versions of NSS prior to 3.26, making it a significant concern for systems that rely on this security library for their cryptographic operations.
The technical mechanism behind this vulnerability involves the improper handling of null pointer references during cryptographic signature computations and record message authentication code calculations within the SSL 3.0 protocol implementation. When processing certain TLS handshake messages or cryptographic operations, the affected functions fail to validate pointer parameters before dereferencing them, creating a scenario where a null pointer is accessed and results in an immediate crash. This type of vulnerability falls under CWE-476, which specifically addresses null pointer dereference conditions, and represents a classic example of improper input validation in cryptographic libraries. The crash occurs during the constant-time computation of record message authentication codes, which is a security-critical operation designed to prevent timing attacks, but ironically becomes exploitable due to the lack of proper null checks.
The operational impact of CVE-2016-5285 extends beyond simple service disruption, as it can be leveraged by attackers to perform targeted denial of service attacks against TLS/SSL servers that utilize the vulnerable NSS library. Systems running web servers, email servers, or any service that relies on NSS for secure communications become vulnerable to crashes that can render them unavailable to legitimate users. The vulnerability is particularly concerning because it affects the core cryptographic operations that are fundamental to secure communications, meaning that exploitation can occur during normal TLS handshakes without requiring special privileges or complex attack vectors. This vulnerability aligns with ATT&CK technique T1499.004, which describes network denial of service attacks targeting cryptographic services, and demonstrates how weaknesses in cryptographic libraries can create widespread security implications across multiple applications and services.
Organizations affected by this vulnerability should prioritize immediate patching of their NSS installations to version 3.26 or later, which contains the necessary fixes for the null pointer dereference conditions. The mitigation strategy should include comprehensive testing of patched systems to ensure that the fix does not introduce compatibility issues with existing applications that depend on NSS. Security teams should also implement monitoring for unusual connection drops or service disruptions that might indicate exploitation attempts, while maintaining awareness of the broader threat landscape for similar vulnerabilities in cryptographic libraries. Additional defensive measures could include implementing network-level protections such as rate limiting for TLS handshake requests and ensuring that systems are configured to use more recent TLS versions that are less susceptible to these types of attacks, as the vulnerability specifically affects SSL 3.0 implementations and related cryptographic operations that are part of the older TLS protocol stack.