CVE-2026-92005 Overview
CVE-2026-92005 is a use-after-free vulnerability [CWE-416] in the Audio/Video: Web Codecs component used by Mozilla Firefox and Thunderbird. The flaw affects how the browser manages memory associated with WebCodecs media processing. An attacker who serves a crafted web page can trigger the condition remotely without authentication or user interaction beyond loading the content. Mozilla addressed the issue in Firefox 156, Firefox ESR 140.16, Firefox ESR 153.3, Thunderbird 156, Thunderbird 140.16, and Thunderbird 153.3.
Critical Impact
Remote attackers can trigger memory corruption in the WebCodecs component through a malicious page, producing availability impact and potential for further exploitation.
Affected Products
- Mozilla Firefox versions prior to 156
- Mozilla Firefox ESR versions prior to 140.16 and 153.3
- Mozilla Thunderbird versions prior to 156, 140.16, and 153.3
Discovery Timeline
- 2026-09-15 - CVE-2026-92005 published to NVD
- 2026-09-17 - Last updated in NVD database
Technical Details for CVE-2026-92005
Vulnerability Analysis
The vulnerability resides in the Audio/Video: Web Codecs component that exposes the WebCodecs API to web content. WebCodecs provides low-level access to encoders and decoders for audio and video frames. A use-after-free condition occurs when code retains a reference to a codec-related object after the underlying memory has been released. Subsequent access to that dangling reference reads or writes freed memory. The result can be a browser crash, memory disclosure, or manipulation of program state depending on how the freed allocation is reused. The reachable attack surface is any content that can instantiate WebCodecs objects, including third-party frames and advertisements.
Root Cause
The root cause is improper object lifetime management inside the WebCodecs implementation. A codec object or backing buffer is freed while another code path still holds a pointer to it. This is a classic [CWE-416] pattern where reference counting, ownership transfer, or asynchronous callback handling fails to keep the object alive for the duration of its use.
Attack Vector
Exploitation requires the victim to load attacker-controlled web content in a vulnerable Firefox or Thunderbird build. The attacker crafts JavaScript that drives the WebCodecs API through a sequence that triggers premature deallocation and subsequent access. No privileges or explicit user interaction beyond page load are required. Thunderbird is affected when remote content is rendered.
No verified public exploit code is available for CVE-2026-92005. See the Mozilla Bug Report #2056051 and Mozilla Security Advisory MFSA-2026-90 for authoritative technical details.
Detection Methods for CVE-2026-92005
Indicators of Compromise
- Unexpected Firefox or Thunderbird process crashes with signatures pointing to WebCodecs decoder or encoder frames.
- Crash reports referencing freed memory access in audio or video codec paths.
- Outbound connections from browser processes to newly registered domains hosting media-heavy content immediately preceding a crash.
Detection Strategies
- Inventory installed Firefox and Thunderbird versions across the fleet and flag builds older than the fixed releases.
- Correlate browser crash telemetry with URL history to identify pages that trigger WebCodecs-related faults.
- Monitor endpoint EDR telemetry for anomalous child process creation or memory allocation patterns originating from firefox.exe or thunderbird.exe.
Monitoring Recommendations
- Ingest Mozilla crash reporter data and browser process telemetry into a centralized data lake for query and correlation.
- Alert on Firefox or Thunderbird processes exhibiting abnormal memory growth or repeated crashes within short intervals.
- Track proxy and DNS logs for user navigation to unfamiliar domains that immediately precede browser instability events.
How to Mitigate CVE-2026-92005
Immediate Actions Required
- Upgrade Firefox to version 156 or later on all managed endpoints.
- Upgrade Firefox ESR deployments to 140.16 or 153.3 depending on the maintained branch.
- Upgrade Thunderbird to 156, 140.16, or 153.3 to remediate the same defect in mail client rendering.
- Prioritize systems that browse untrusted content or process external email with remote content enabled.
Patch Information
Mozilla fixed CVE-2026-92005 in Firefox 156, Firefox ESR 140.16, Firefox ESR 153.3, Thunderbird 156, Thunderbird 140.16, and Thunderbird 153.3. Refer to Mozilla Security Advisory MFSA-2026-90, MFSA-2026-92, MFSA-2026-93, MFSA-2026-94, MFSA-2026-95, and MFSA-2026-96 for full release mappings.
Workarounds
- Disable remote content rendering in Thunderbird until the client is patched.
- Enforce browser update policies through group policy or mobile device management to remove outdated versions.
- Restrict access to untrusted media-rich sites through web filtering while patch rollout is in progress.
# Configuration example: verify installed Firefox version on Linux endpoints
firefox --version
# Windows: query installed version via registry
reg query "HKLM\SOFTWARE\Mozilla\Mozilla Firefox" /v CurrentVersion
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
