CVE-2026-6772: Mozilla Firefox Buffer Overflow Vulnerability

CVE-2026-6772 Overview

CVE-2026-6772 is a boundary condition error vulnerability affecting the Network Security Services (NSS) Libraries component used by Mozilla Firefox and Thunderbird. The flaw stems from improper exceptional conditions handling (CWE-754), which can allow remote attackers to exploit incorrect boundary validation to access sensitive information over the network without requiring user interaction or authentication.

Critical Impact
Remote attackers can exploit this network-accessible vulnerability to compromise confidentiality of data processed by affected Mozilla products, potentially leading to unauthorized information disclosure.

Affected Products

Mozilla Firefox (versions prior to 150)
Mozilla Firefox ESR (versions prior to 115.35 and 140.10)
Mozilla Thunderbird (versions prior to 150 and 140.10)

Discovery Timeline

April 21, 2026 - CVE-2026-6772 published to NVD
April 22, 2026 - Last updated in NVD database

Technical Details for CVE-2026-6772

Vulnerability Analysis

This vulnerability exists within the NSS (Network Security Services) Libraries component, which is a critical cryptographic library used by Mozilla products for SSL/TLS and other security functions. The flaw is classified as CWE-754 (Improper Check for Unusual or Exceptional Conditions), indicating that the code fails to properly handle boundary conditions during data processing operations.

The vulnerability is network-accessible and can be exploited remotely without any privileges or user interaction. Successful exploitation could result in unauthorized access to confidential information processed by the affected applications, though it does not appear to impact system integrity or availability.

Root Cause

The root cause of CVE-2026-6772 lies in incorrect boundary condition handling within the NSS Libraries component. The code fails to properly validate exceptional conditions when processing certain inputs, leading to improper data handling that can expose sensitive information. This type of flaw typically occurs when input validation routines do not account for edge cases or unusual input patterns.

Attack Vector

The attack vector for this vulnerability is network-based, allowing remote exploitation. An attacker can craft malicious network traffic targeting the vulnerable NSS library component in Firefox or Thunderbird. The attack requires:

Network access to the target system
No authentication or user interaction
Exploitation of the boundary condition error to trigger information disclosure

The vulnerability manifests when the NSS library processes crafted input that triggers the improper boundary condition check, potentially allowing extraction of sensitive data. For detailed technical information, refer to the Mozilla Bug Report #2026089.

Detection Methods for CVE-2026-6772

Indicators of Compromise

Unusual network traffic patterns targeting Firefox or Thunderbird processes
Unexpected memory access patterns or crashes in NSS library components
Anomalous SSL/TLS handshake behavior in affected applications

Detection Strategies

Monitor for exploitation attempts by analyzing network traffic for malformed or suspicious requests targeting Mozilla applications
Deploy intrusion detection signatures that identify boundary condition exploitation patterns in NSS-related traffic
Implement application-level monitoring to detect abnormal behavior in Firefox and Thunderbird processes

Monitoring Recommendations

Enable verbose logging for Firefox and Thunderbird to capture potential exploitation attempts
Monitor system processes for unexpected crashes or memory violations in nss3.dll or libnss3.so libraries
Implement network-level monitoring to detect potential data exfiltration following successful exploitation

How to Mitigate CVE-2026-6772

Immediate Actions Required

Update Mozilla Firefox to version 150 or later immediately
Update Mozilla Firefox ESR to version 115.35 or 140.10 or later
Update Mozilla Thunderbird to version 150 or 140.10 or later
Verify all endpoints have received the security updates through enterprise software management tools

Patch Information

Mozilla has released security patches addressing this vulnerability across multiple product lines. Organizations should apply the following updates:

Firefox 150 - Standard release with the fix
Firefox ESR 115.35 - Extended Support Release patch
Firefox ESR 140.10 - Extended Support Release patch
Thunderbird 150 - Standard release with the fix
Thunderbird 140.10 - ESR release with the fix

For detailed information, review the official Mozilla Security Advisories:

Workarounds

Limit network exposure of affected systems until patches can be applied
Consider using network segmentation to isolate systems running vulnerable versions
Implement egress filtering to limit potential data exfiltration if exploitation occurs

bash

# Verify Firefox version on Linux/macOS
firefox --version

# Verify Thunderbird version
thunderbird --version

# For enterprise deployments, use package manager to update
# Debian/Ubuntu
sudo apt update && sudo apt upgrade firefox thunderbird

# RHEL/CentOS/Fedora
sudo dnf update firefox thunderbird