CVE-2026-92043: Firefox Audio/Video Privilege Escalation

CVE-2026-92043 Overview

CVE-2026-92043 is a privilege escalation vulnerability in the Audio/Video component of Mozilla Firefox and Thunderbird. The flaw stems from incorrect boundary conditions [CWE-120] that allow an attacker to overrun buffers during media processing. Mozilla addressed the issue in Firefox 156, Firefox ESR 153.3, Thunderbird 156, and Thunderbird 153.3. Successful exploitation requires user interaction, such as visiting a malicious page or opening crafted media content, but no prior privileges are needed. The vulnerability affects confidentiality, integrity, and availability at a high level.

Critical Impact
A remote attacker can escalate privileges within the browser sandbox by delivering crafted audio or video content, leading to arbitrary code execution in the context of the browser process.

Affected Products

Mozilla Firefox versions prior to 156
Mozilla Firefox ESR versions prior to 153.3
Mozilla Thunderbird versions prior to 156 and prior to 153.3

Discovery Timeline

2026-09-15 - CVE-2026-92043 published to NVD
2026-09-16 - Last updated in NVD database

Technical Details for CVE-2026-92043

Vulnerability Analysis

The vulnerability resides in the Audio/Video component responsible for decoding and rendering media streams inside Firefox and Thunderbird. Incorrect boundary conditions during buffer handling allow memory adjacent to media buffers to be read or written outside intended limits. An attacker who serves crafted media content can trigger the condition when the victim loads a webpage or opens an email that renders media.

Because the Audio/Video pipeline runs with elevated privileges relative to untrusted web content, exploitation can lead to a privilege escalation within the browser process. The result is potential arbitrary code execution and full compromise of the browser session, including access to cookies, credentials, and cached content.

Root Cause

The root cause is a classic buffer boundary miscalculation classified under [CWE-120] (Buffer Copy without Checking Size of Input). The Audio/Video component fails to correctly validate size parameters before performing memory operations on media frames. Malformed container metadata or codec parameters can cause the affected routine to compute an incorrect boundary, enabling out-of-bounds access.

Attack Vector

Exploitation occurs over the network and requires user interaction. An attacker hosts crafted audio or video content on a website, embeds it in a page, or delivers it through an HTML email opened in Thunderbird. When the victim's browser or mail client renders the content, the vulnerable decoder path is invoked and the boundary violation is triggered. No authentication is required.

No public proof-of-concept exploit is available for CVE-2026-92043 at the time of publication. Refer to the Mozilla Security Advisory MFSA-2026-90 and related advisories (MFSA-2026-93, MFSA-2026-94, MFSA-2026-96) for further technical context. Additional details are tracked in Mozilla Bug #2050150.

Detection Methods for CVE-2026-92043

Indicators of Compromise

Unexpected Firefox or Thunderbird process crashes with signatures pointing at audio or video decoder frames.
Child content processes spawning unusual subprocesses or making outbound connections shortly after loading media content.
Media files with malformed container metadata delivered from untrusted origins.

Detection Strategies

Inventory Firefox and Thunderbird installations across the environment and flag versions below Firefox 156, Firefox ESR 153.3, or Thunderbird 156/153.3.
Monitor endpoint telemetry for anomalous behavior originating from browser or mail client processes, including memory access violations in media libraries.
Correlate web proxy logs with delivery of unusual audio or video MIME types from newly registered or low-reputation domains.

Monitoring Recommendations

Enable process and file telemetry for firefox.exe, thunderbird.exe, and their Linux and macOS equivalents.
Alert on browser child processes spawning shells, script interpreters, or performing credential file access.
Track patch compliance via configuration management tooling and generate alerts for hosts running unpatched Mozilla builds.

How to Mitigate CVE-2026-92043

Immediate Actions Required

Upgrade Firefox to version 156 or later and Firefox ESR to 153.3 or later on all managed endpoints.
Upgrade Thunderbird to version 156 or 153.3 or later, prioritizing systems that render HTML email with remote media.
Restrict autoplay and remote content loading in Thunderbird until patches are deployed across the fleet.

Patch Information

Mozilla shipped fixes for CVE-2026-92043 in Firefox 156, Firefox ESR 153.3, Thunderbird 156, and Thunderbird 153.3. Patch details are documented in the Mozilla Security Advisory MFSA-2026-90, MFSA-2026-93, MFSA-2026-94, and MFSA-2026-96. Administrators using enterprise policy management should push updates through their standard software distribution pipeline.

Workarounds

Configure Thunderbird to block remote content in messages until the update is applied.
Use enterprise policy to disable autoplay of audio and video in Firefox for untrusted origins.
Route browser traffic through a web filtering solution that blocks known malicious domains delivering crafted media.

bash

# Example: enforce disabling autoplay via Firefox enterprise policy (policies.json)
{
  "policies": {
    "Permissions": {
      "Autoplay": {
        "Default": "block-audio-video"
      }
    },
    "DisableAppUpdate": false
  }
}