CVE-2016-1950

What it actually does

Heap-based buffer overflow in NSS during ASN.1 parsing of X.509 certificates allows remote attackers to execute arbitrary code.

Why it matters to the business

Remote compromise of systems processing untrusted certificates can lead to full system takeover, data theft, or deployment of persistent malware across affected browsers and servers.

How an attack unfolds

An attacker crafts a malicious X.509 certificate containing malformed ASN.1 data, then delivers it to a victim through a web page, email attachment, or TLS handshake; when the vulnerable NSS library parses the certificate, the overflow occurs and attacker-controlled code executes.

How to fix it

Upgrade Mozilla NSS to 3.19.2.3 or 3.21.1 (or later) and Firefox to 45.0 or ESR 38.7 (or later); apply equivalent patches to downstream products such as Oracle Linux, Apple platforms, and OpenSUSE.

How to confirm the fix worked

Verify installed NSS and Firefox versions against the fixed releases; use package managers or vulnerability scanners to confirm absence of vulnerable NSS libraries.

Typical attack path

1. Craft X.509 certificate with oversized or malformed ASN.1 structures
2. Host the certificate on a malicious web server or embed in a TLS handshake
3. Trick victim into visiting the site or initiating a connection that triggers certificate validation
4. Trigger heap overflow during NSS parsing to gain code execution
5. Install payload or pivot within the compromised process

How to detect it

Review application and system logs for NSS crashes or segmentation faults during certificate validation; correlate with web proxy or browser history showing visits to suspicious domains around the time of anomalous process behavior.

What your security team should do

• Immediately update all instances of NSS and Firefox to the patched releases
• Block untrusted certificate sources and enforce certificate pinning where feasible
• Scan enterprise endpoints for vulnerable NSS versions and prioritize high-exposure systems
• Monitor for any delayed exploitation given the age of the vulnerability