CVE-2016-1978 in Firefox
Summary
by MITRE
Use-after-free vulnerability in the ssl3_HandleECDHServerKeyExchange function in Mozilla Network Security Services (NSS) before 3.21, as used in Mozilla Firefox before 44.0, allows remote attackers to cause a denial of service or possibly have unspecified other impact by making an SSL (1) DHE or (2) ECDHE handshake at a time of high memory consumption.
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Analysis
by VulDB Data Team • 07/09/2022
The CVE-2016-1978 vulnerability represents a critical use-after-free flaw within Mozilla Network Security Services NSS library, specifically affecting the ssl3_HandleECDHServerKeyExchange function. This vulnerability exists in NSS versions prior to 3.21 and impacts Mozilla Firefox versions before 44.0, creating a significant security risk for web browsers that rely on this cryptographic library for secure communications. The flaw manifests during SSL handshake operations when processing ECDHE (Elliptic Curve Diffie-Hellman Ephemeral) key exchanges, making it particularly dangerous in high-traffic network environments where memory pressure is common.
The technical implementation of this vulnerability stems from improper memory management within the SSL 3.0 protocol handling code. During the ECDH server key exchange process, the ssl3_HandleECDHServerKeyExchange function fails to properly validate memory references after certain operations, leading to a scenario where freed memory locations are accessed or reused. This use-after-free condition occurs specifically when the system encounters high memory consumption scenarios, which is a common occurrence in web server environments or during heavy network traffic periods. The vulnerability is triggered when an attacker can manipulate the SSL handshake process to force the system into a state where memory is freed and subsequently accessed, potentially leading to application crashes or more severe consequences.
The operational impact of this vulnerability extends beyond simple denial of service attacks, as the flaw could potentially enable more sophisticated exploitation techniques. When attackers can force memory allocation and deallocation patterns during SSL handshakes, they may be able to manipulate the memory layout to achieve arbitrary code execution or information disclosure. The vulnerability's effectiveness is heightened during high memory consumption periods, suggesting that it could be particularly dangerous in resource-constrained environments or when multiple concurrent connections are established. This makes the vulnerability especially concerning for web servers and applications that handle numerous simultaneous SSL connections, as the likelihood of triggering the condition increases significantly.
Security professionals should recognize this vulnerability as a classic example of memory safety issues that align with CWE-416, which describes the use of freed memory condition. The attack vector requires remote execution capabilities, making it suitable for exploitation through network-based attacks, and aligns with ATT&CK technique T1059.007 for remote code execution through network services. Organizations should prioritize immediate patching of affected systems, particularly those running older versions of Firefox or NSS libraries. The remediation strategy involves upgrading to NSS 3.21 or later versions and Firefox 44.0 or higher, which include proper memory management fixes. Additionally, network administrators should consider implementing monitoring for unusual SSL handshake patterns and memory consumption spikes that could indicate exploitation attempts. Regular security assessments and vulnerability scanning should be conducted to ensure all systems remain protected against similar memory-related vulnerabilities that could potentially be exploited in similar cryptographic contexts.