CVE-2026-4695 Overview
CVE-2026-4695 is a boundary condition error vulnerability affecting the Audio/Video: Web Codecs component in Mozilla Firefox and Thunderbird. The vulnerability stems from improper validation of exceptional conditions (CWE-754) within the media processing functionality, which can be exploited remotely over the network without requiring user interaction or authentication.
This flaw enables attackers to trigger denial of service conditions by sending specially crafted media content that causes the browser to improperly handle boundary conditions during codec processing. The vulnerability affects multiple Mozilla products including Firefox, Firefox ESR, and Thunderbird across various versions.
Critical Impact
Remote attackers can exploit incorrect boundary conditions in the Web Codecs component to cause high-impact denial of service, affecting system availability without requiring any user interaction.
Affected Products
- Mozilla Firefox versions prior to 149
- Mozilla Firefox ESR versions prior to 140.9
- Mozilla Thunderbird versions prior to 149 and 140.9
Discovery Timeline
- 2026-03-24 - CVE-2026-4695 published to NVD
- 2026-03-26 - Last updated in NVD database
Technical Details for CVE-2026-4695
Vulnerability Analysis
The vulnerability resides in the Audio/Video: Web Codecs component, a critical subsystem responsible for encoding and decoding media streams in Mozilla browsers. The root cause involves improper handling of exceptional conditions during boundary validation, classified as CWE-754 (Improper Check for Unusual or Exceptional Conditions).
When processing media content, the Web Codecs component fails to properly validate boundary conditions, allowing malformed input to bypass security checks. This can result in resource exhaustion or component crashes, leading to denial of service. The network-based attack vector with low complexity makes this vulnerability particularly concerning for organizations relying on Mozilla products for daily operations.
Root Cause
The underlying issue stems from inadequate boundary condition checking in the Web Codecs processing logic. The component does not properly validate input parameters or handle edge cases when processing audio/video codec data, leading to exceptional conditions that can crash the application or consume excessive resources. This represents a failure to implement defensive programming practices for unusual input scenarios.
Attack Vector
The vulnerability is exploitable remotely via the network. An attacker can craft malicious media content designed to trigger the improper boundary condition handling. When a user browses to a malicious website or loads affected media content in Firefox or Thunderbird, the Web Codecs component processes the malformed data, triggering the vulnerability.
No user interaction is required beyond normal browsing behavior, and no prior authentication is needed. The attack primarily impacts system availability by causing denial of service conditions, though confidentiality and integrity remain unaffected.
Technical details regarding the specific vulnerable code paths are available in the Mozilla Bug Report #2020030 and related security advisories.
Detection Methods for CVE-2026-4695
Indicators of Compromise
- Repeated Firefox or Thunderbird crashes when accessing specific websites or media content
- Unusual memory consumption patterns in browser processes during media playback
- Application freezes or hangs when loading audio/video content via Web Codecs API
- Error logs indicating codec processing failures or boundary validation errors
Detection Strategies
- Monitor browser crash reports and correlate with recently visited URLs containing media content
- Implement network-level inspection for malformed media streams targeting Web Codecs
- Deploy endpoint detection and response (EDR) solutions to identify abnormal browser behavior patterns
- Review application logs for exceptions related to audio/video codec processing
Monitoring Recommendations
- Enable enhanced logging for browser media subsystems to capture codec-related errors
- Configure SentinelOne agents to monitor for repeated application crashes in Mozilla products
- Implement alerting for high resource consumption by Firefox or Thunderbird processes
- Monitor network traffic for known malicious media hosting domains
How to Mitigate CVE-2026-4695
Immediate Actions Required
- Update Mozilla Firefox to version 149 or later immediately
- Update Mozilla Firefox ESR to version 140.9 or later
- Update Mozilla Thunderbird to version 149 or 140.9 or later
- Verify all browser instances across the organization are updated using asset management tools
Patch Information
Mozilla has released security patches addressing this vulnerability across all affected product lines. Organizations should prioritize updating to the following minimum versions:
- Firefox: Version 149 or later
- Firefox ESR: Version 140.9 or later
- Thunderbird: Version 149 or 140.9 or later
For detailed patch information, refer to Mozilla Security Advisory MFSA-2026-20 and Mozilla Security Advisory MFSA-2026-22.
Workarounds
- Disable automatic media playback in browser settings to reduce exposure to malicious media content
- Implement content filtering to block access to untrusted media sources
- Consider using browser extensions that limit codec usage on untrusted sites
- Deploy network-level controls to inspect and sanitize media content before reaching endpoints
# Firefox configuration to disable automatic media playback
# Access about:config and set the following preferences
# media.autoplay.default = 5 (Block Audio and Video)
# media.autoplay.blocking_policy = 2 (Strict blocking)
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
