CVE-2025-13013: Mozilla Firefox Auth Bypass Vulnerability

CVE-2025-13013 Overview

CVE-2025-13013 is a mitigation bypass vulnerability in the DOM: Core & HTML component of Mozilla Firefox and Thunderbird. The flaw enables an attacker-controlled web page to circumvent a built-in browser security mitigation. Successful exploitation requires user interaction, such as visiting a malicious page, and can result in a scope change with limited impact to both confidentiality and integrity. Mozilla addressed the issue in Firefox 145, Firefox ESR 140.5, Firefox ESR 115.30, Thunderbird 145, and Thunderbird 140.5. The vulnerability is tracked under [CWE-288] (Authentication Bypass Using an Alternate Path or Channel).

Critical Impact
A remote attacker can bypass a DOM security mitigation via a crafted web page, breaking cross-origin protections that shield users from malicious content.

Affected Products

Mozilla Firefox versions prior to 145
Mozilla Firefox ESR versions prior to 140.5 and 115.30
Mozilla Thunderbird versions prior to 145 and 140.5

Discovery Timeline

2025-11-11 - CVE-2025-13013 published to NVD
2026-06-17 - Last updated in NVD database

Technical Details for CVE-2025-13013

Vulnerability Analysis

The vulnerability resides in the DOM: Core & HTML component, which handles Document Object Model parsing and rendering in the Gecko engine. Mozilla classifies the issue as a mitigation bypass, meaning an existing browser defense can be circumvented under attacker-controlled conditions. Because the flaw allows a scope change, an attacker can affect resources beyond the vulnerable component's security authority, typically crossing origin boundaries. Exploitation requires user interaction such as navigating to a crafted page or clicking a malicious link.

Root Cause

The root cause is tracked as [CWE-288], an authentication bypass using an alternate path or channel. According to Mozilla's advisories MFSA-2025-87 through MFSA-2025-91, the DOM code path did not consistently enforce the intended security check, allowing an alternate route to reach protected functionality. Full technical details are restricted in Mozilla Bugzilla entry 1991945 while users update.

Attack Vector

The attack is delivered over the network. An attacker hosts a malicious web page or embeds malicious content that, when loaded by a vulnerable Firefox or Thunderbird build, triggers the bypass. No credentials are needed on the target system, but the victim must load the content. The result is limited disclosure or modification of data that should have been protected by the bypassed mitigation.

No verified proof-of-concept code has been published. See the Mozilla Bug Report #1991945 and Mozilla Security Advisory MFSA-2025-87 for further technical context.

Detection Methods for CVE-2025-13013

Indicators of Compromise

Firefox or Thunderbird processes loading content from newly registered or low-reputation domains followed by unexpected cross-origin requests.
Browser telemetry showing DOM policy violations, sandbox escapes, or unexpected script execution across origins.
Endpoint logs recording outdated Firefox or Thunderbird versions still in use after the November 2025 patch cycle.

Detection Strategies

Inventory installed Firefox and Thunderbird versions across the fleet and flag any build below the fixed versions listed in MFSA-2025-87 through MFSA-2025-91.
Monitor web proxy and DNS logs for connections to suspicious domains hosting exploit content targeting browsers.
Correlate browser process activity with child process spawns or file writes that deviate from baseline behavior.

Monitoring Recommendations

Enable browser update telemetry and alert when endpoints fall behind the vendor's current release channel.
Track user reports of unexpected browser prompts, redirects, or content behavior that may indicate exploitation attempts.
Review email gateway logs for messages containing links that render in Thunderbird's HTML view, as the same engine is affected.

How to Mitigate CVE-2025-13013

Immediate Actions Required

Update Firefox to version 145 or later on all supported operating systems.
Update Firefox ESR deployments to 140.5 or 115.30, depending on the ESR channel in use.
Update Thunderbird to version 145 or 140.5 to remediate the shared Gecko code path.
Prioritize systems used for general web browsing and email rendering, since exploitation requires only user interaction.

Patch Information

Mozilla shipped fixes across multiple advisories: MFSA-2025-87, MFSA-2025-88, MFSA-2025-89, MFSA-2025-90, and MFSA-2025-91. Enterprises using managed deployments should push the updated MSI or PKG packages through their software distribution platform and verify version compliance.

Workarounds

No official workaround exists. Apply the vendor patch to eliminate the vulnerability.
Restrict browsing to trusted sites through web filtering while patches are staged.
Disable JavaScript for high-risk users via enterprise policy until updates are deployed, understanding the usability impact.

bash

# Verify Firefox version on Linux endpoints
firefox --version
# Expected output for patched builds:
#   Mozilla Firefox 145.0  (or ESR 140.5 / 115.30)

# Windows PowerShell inventory query
Get-ItemProperty "HKLM:\SOFTWARE\Mozilla\Mozilla Firefox" | Select-Object CurrentVersion