CVE-2016-9574 in NSS
Summary
by MITRE
nss before version 3.30 is vulnerable to a remote denial of service during the session handshake when using SessionTicket extension and ECDHE-ECDSA.
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Analysis
by VulDB Data Team • 04/18/2023
The vulnerability identified as CVE-2016-9574 affects the Network Security Services library version 3.30 and earlier, presenting a remote denial of service condition during SSL/TLS session handshake processes. This weakness specifically manifests when the SessionTicket extension is utilized in conjunction with ECDHE-ECDSA cipher suites, creating a scenario where malicious actors can exploit the protocol implementation to disrupt legitimate service availability. The issue resides in the handling of session resumption mechanisms within the cryptographic library that governs secure communications across numerous applications and systems relying on NSS for security operations.
The technical flaw stems from improper validation and processing of SessionTicket data structures when ECDHE-ECDSA key exchange mechanisms are employed during TLS handshakes. During the session resumption phase, the NSS library fails to adequately validate the integrity and structure of received session tickets, allowing specially crafted malicious tickets to trigger unexpected behavior in the cryptographic processing routines. This validation gap enables attackers to construct session tickets that cause the library to enter an inconsistent state or execute erroneous code paths, ultimately leading to application termination or system instability. The vulnerability operates at the protocol implementation level rather than the cryptographic algorithm itself, making it particularly insidious as it leverages legitimate protocol features to achieve denial of service outcomes.
The operational impact of this vulnerability extends across numerous systems and applications that depend on NSS for secure communications, including web browsers, email clients, and server applications implementing TLS security. Attackers can remotely initiate denial of service conditions by presenting malformed session tickets during handshake negotiations, potentially causing service disruption for legitimate users and creating opportunities for broader attacks. This vulnerability particularly affects environments where ECDHE-ECDSA cipher suites are commonly used, which include many modern secure web applications and services. The remote nature of the exploit means that attackers do not require local access or authentication credentials, making the vulnerability highly dangerous in production environments where service availability is critical.
Mitigation strategies for CVE-2016-9574 primarily involve upgrading to NSS version 3.30 or later, where the vulnerability has been addressed through improved session ticket validation mechanisms. Organizations should implement comprehensive patch management procedures to ensure all systems utilizing NSS components receive timely updates. Additionally, administrators can temporarily disable ECDHE-ECDSA cipher suites or SessionTicket extension usage as interim protective measures while full patches are deployed. The vulnerability aligns with CWE-248, which addresses improper exception handling in software implementations, and demonstrates characteristics consistent with ATT&CK technique T1499.004 related to network denial of service attacks. Security monitoring should focus on detecting unusual session handshake patterns and potential malformed session ticket traffic that could indicate exploitation attempts. Organizations should also consider implementing network segmentation and intrusion detection systems to identify and block malicious session ticket traffic patterns that could indicate exploitation of this vulnerability.