CVE-2015-5244 in mod_nss
Summary
by MITRE
The NSSCipherSuite option with ciphersuites enabled in mod_nss before 1.0.12 allows remote attackers to bypass application restrictions.
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Analysis
by VulDB Data Team • 12/15/2022
The vulnerability identified as CVE-2015-5244 affects the mod_nss module, which provides SSL/TLS capabilities for the Apache HTTP Server through integration with the Network Security Services library. This issue specifically relates to the NSSCipherSuite configuration directive that controls which cryptographic cipher suites are permitted for secure communications. The flaw enables remote attackers to circumvent application-level restrictions that should otherwise prevent the use of certain cipher suites, potentially undermining the security posture of web applications relying on this module.
The technical implementation of this vulnerability stems from improper validation within the mod_nss module's handling of cipher suite configurations. When administrators configure the NSSCipherSuite option to restrict which ciphersuites can be used, the module fails to properly enforce these restrictions in all scenarios. This occurs due to insufficient input validation and state management within the SSL handshake process, allowing attackers to negotiate connections using cipher suites that should have been disabled or restricted by the application configuration. The vulnerability is particularly concerning because it operates at the protocol level during TLS negotiation, making it difficult to detect through standard network monitoring.
The operational impact of CVE-2015-5244 extends beyond simple protocol compliance violations, as it can enable attackers to downgrade cryptographic security to weaker cipher suites that are more susceptible to various attacks including man-in-the-middle and cryptographic breakage. This vulnerability aligns with CWE-295, which addresses improper certificate validation, and can be categorized under ATT&CK technique T1566 for credential access through network sniffing and protocol manipulation. Organizations using mod_nss with restricted cipher suite configurations may unknowingly expose their systems to attacks that exploit this bypass mechanism, potentially allowing adversaries to access sensitive data or establish unauthorized secure connections.
Mitigation strategies for this vulnerability require immediate patching of the mod_nss module to version 1.0.12 or later, which contains the necessary fixes to properly enforce cipher suite restrictions. Administrators should also conduct comprehensive audits of their SSL/TLS configurations to identify any potential misconfigurations that could be exploited in conjunction with this vulnerability. Additional protective measures include implementing strict cipher suite policies, regularly monitoring SSL handshake logs for unauthorized cipher suite usage, and ensuring that all systems are configured to use only strong, modern cipher suites that meet current security standards. Network segmentation and monitoring solutions should be deployed to detect anomalous SSL/TLS behavior that might indicate exploitation attempts. The vulnerability demonstrates the critical importance of proper cryptographic implementation and configuration management in web server security, particularly when dealing with SSL/TLS protocols that are fundamental to secure communications.