CVE-2026-92030: Firefox Auth Bypass Vulnerability

CVE-2026-92030 Overview

CVE-2026-92030 is a mitigation bypass vulnerability in the DOM Copy & Paste and Drag & Drop component of Mozilla Firefox and Thunderbird. The flaw allows an attacker-controlled web page to circumvent security mitigations that govern how clipboard and drag-and-drop data are processed within the Document Object Model (DOM). Mozilla addressed the issue across multiple release trains, including Firefox 156, Firefox ESR 140.16, Firefox ESR 153.3, Thunderbird 156, Thunderbird 140.16, and Thunderbird 153.3. The vulnerability is tracked through Mozilla Foundation Security Advisories MFSA-2026-90 and MFSA-2026-92 through MFSA-2026-96.

Critical Impact
A successful bypass weakens DOM security boundaries that protect users during clipboard and drag-and-drop interactions, potentially enabling data-injection or content-spoofing scenarios in the browser and email client.

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-2026-92030 published to NVD
2026-09-16 - Last updated in NVD database

Technical Details for CVE-2026-92030

Vulnerability Analysis

The vulnerability resides in the DOM subsystem responsible for handling copy, paste, and drag-and-drop events. Browsers enforce mitigations on these operations because clipboard and drag payloads cross trust boundaries between the user, origin sites, and the browser chrome. The bypass allows a crafted page to defeat one of these safeguards, expanding the ways an attacker can influence content transferred through DOM clipboard or drag APIs. Because Thunderbird shares the Gecko rendering engine with Firefox, the flaw impacts both products across their supported release channels.

Root Cause

Mozilla has not published detailed root-cause information for CVE-2026-92030 in the referenced advisories. The public description states only that a mitigation in the DOM Copy & Paste and Drag & Drop component can be bypassed. Additional technical detail is tracked in Mozilla Bug Report #2058417, which may be access-restricted pending broader patch adoption.

Attack Vector

Exploitation requires a user to visit or interact with attacker-controlled web content in a vulnerable Firefox or Thunderbird build. The attacker leverages DOM clipboard or drag-and-drop APIs to trigger the bypass during a legitimate user action, such as pasting content or dropping data into a page. No verified public proof-of-concept exists at the time of publication. Refer to Mozilla Security Advisory MFSA-2026-90 and the related advisories for scope guidance across each product build.

Detection Methods for CVE-2026-92030

Indicators of Compromise

No public indicators of compromise have been published for CVE-2026-92030.
Anomalous clipboard or drag-and-drop activity originating from untrusted origins may warrant review.

Detection Strategies

Inventory Firefox and Thunderbird installations and compare installed versions against the fixed builds listed in the Mozilla advisories.
Monitor endpoint software inventory feeds for browser versions below Firefox 156, ESR 140.16, or ESR 153.3.
Review browser telemetry or enterprise policy reporting for out-of-date Gecko-based clients.

Monitoring Recommendations

Track outbound web traffic from endpoints running unpatched browser builds for interactions with unknown or newly registered domains.
Alert on Thunderbird instances rendering remote HTML content while running vulnerable versions.
Correlate patch-compliance data with user-agent strings observed at web proxies to identify lagging endpoints.

How to Mitigate CVE-2026-92030

Immediate Actions Required

Upgrade Firefox to version 156 or later, and Firefox ESR to 140.16 or 153.3 as appropriate for your channel.
Upgrade Thunderbird to version 156, 140.16, or 153.3 depending on the deployed release train.
Prioritize patching on endpoints where users routinely interact with untrusted web content or external email.

Patch Information

Mozilla has released fixes across all supported release trains. Consult Mozilla Security Advisory MFSA-2026-92, MFSA-2026-93, MFSA-2026-94, MFSA-2026-95, and MFSA-2026-96 for the exact product build that applies to your environment.

Workarounds

No vendor-published workarounds are available; applying the patched builds is the recommended remediation.
Enforce enterprise update policies to accelerate rollout of Firefox and Thunderbird updates.
Restrict rendering of untrusted HTML in Thunderbird by disabling remote content in messages until updates are applied.

bash

# Example: verify installed Firefox version on Linux endpoints
firefox --version
# Expected output for patched build: Mozilla Firefox 156.0 or later