CVE-2026-12319: Mozilla Firefox DOS Vulnerability

CVE-2026-12319 Overview

CVE-2026-12319 is a denial-of-service vulnerability in the Audio/Video: Playback component of Mozilla Firefox and Mozilla Thunderbird. The flaw allows a remote attacker to crash or exhaust resources in affected applications when a victim loads attacker-controlled media content. The issue is categorized under [CWE-400] Uncontrolled Resource Consumption. Mozilla addressed the vulnerability in Firefox 152 and Thunderbird 152.

Critical Impact
A network-based attacker can trigger a high-availability impact on Firefox and Thunderbird users by serving crafted audio or video content, causing application disruption and loss of access to browser or mail functionality.

Affected Products

Mozilla Firefox (versions prior to 152)
Mozilla Thunderbird (versions prior to 152)
Audio/Video: Playback component in both products

Discovery Timeline

2026-06-16 - CVE-2026-12319 published to NVD
2026-06-17 - Last updated in NVD database
Mozilla published advisories MFSA-2026-57 and MFSA-2026-60 covering this fix

Technical Details for CVE-2026-12319

Vulnerability Analysis

The vulnerability resides in the Audio/Video: Playback subsystem responsible for decoding and rendering media streams in Firefox and Thunderbird. Improper handling of media data leads to uncontrolled resource consumption, classified under [CWE-400]. When a user loads a page or message referencing maliciously crafted media, the playback pipeline consumes excessive memory or CPU resources. This results in application unresponsiveness or termination. The flaw requires user interaction, such as visiting a web page or opening an HTML email that auto-loads remote content.

Root Cause

The root cause is insufficient bounds or rate enforcement on data flowing through the Audio/Video: Playback component. Mozilla's advisories MFSA-2026-57 and MFSA-2026-60 confirm the issue was corrected in version 152 of both products. Refer to Mozilla Bug Report #2026933 for technical details on the corrected code path.

Attack Vector

Exploitation is remote and requires user interaction. An attacker hosts crafted audio or video content on a controlled site or embeds it in an HTML email. When the victim's Firefox or Thunderbird client processes the media, the playback engine consumes resources until the application becomes unusable. No authentication is required, and no confidentiality or integrity impact has been reported. Verified code or proof-of-concept artifacts are not publicly available. See the Mozilla Security Advisory MFSA-2026-57 and Mozilla Security Advisory MFSA-2026-60 for vendor details.

Detection Methods for CVE-2026-12319

Indicators of Compromise

Repeated Firefox or Thunderbird process crashes or hangs correlated with media playback activity.
Spikes in CPU or memory consumption by firefox.exe, firefox, or thunderbird processes when rendering remote audio/video content.
Browser or mail client telemetry showing abnormal terminations in the media decoder threads.

Detection Strategies

Monitor endpoint telemetry for unexpected termination of firefox or thunderbird processes coinciding with network requests to media URLs.
Inspect web proxy and DNS logs for connections to untrusted domains delivering audio or video MIME types to vulnerable client versions.
Correlate user-reported crashes with installed Mozilla version data to identify hosts running pre-152 builds.

Monitoring Recommendations

Inventory Firefox and Thunderbird versions across the fleet and flag any installation below version 152.
Alert on browser crash dumps generated by media decoder modules.
Track outbound HTTP/HTTPS sessions delivering large or anomalous media payloads to clients running unpatched Mozilla builds.

How to Mitigate CVE-2026-12319

Immediate Actions Required

Upgrade Mozilla Firefox to version 152 or later on all managed endpoints.
Upgrade Mozilla Thunderbird to version 152 or later on all managed endpoints.
Enable automatic updates for both products to ensure timely delivery of future security fixes.

Patch Information

Mozilla released fixes in Firefox 152 and Thunderbird 152. Administrators should consult Mozilla Security Advisory MFSA-2026-57 and Mozilla Security Advisory MFSA-2026-60 for affected version ranges and deployment guidance. The corresponding bug tracker entry is available at Mozilla Bug Report #2026933.

Workarounds

Configure Thunderbird to block remote content in messages until the patch is deployed.
Restrict autoplay of audio and video in Firefox via enterprise policy until upgrades complete.
Use network controls to limit access to untrusted media-hosting domains for hosts that cannot be patched immediately.

bash

# Configuration example: Firefox enterprise policy to block media autoplay
# policies.json deployed to the Firefox distribution directory
{
  "policies": {
    "Permissions": {
      "Autoplay": {
        "Default": "block-audio-video"
      }
    },
    "DisableAppUpdate": false
  }
}