CVE-2026-92025: Firefox Use-After-Free Vulnerability

CVE-2026-92025 Overview

CVE-2026-92025 is a use-after-free vulnerability in the DOM: Navigation component of Mozilla Firefox and Thunderbird. The flaw affects how the browser engine manages memory during navigation operations within the Document Object Model (DOM). Mozilla addressed the issue across multiple product lines, including Firefox, Firefox Extended Support Release (ESR), and Thunderbird.

Critical Impact
A successful exploit could allow an attacker to trigger memory corruption through crafted web content, potentially leading to arbitrary code execution within the browser process.

Affected Products

Mozilla Firefox versions prior to 156
Mozilla Firefox ESR versions prior to 115.41, 140.16, and 153.3
Mozilla Thunderbird versions prior to 156, 140.16, and 153.3

Discovery Timeline

2026-09-15 - CVE-2026-92025 published to the National Vulnerability Database (NVD)
2026-09-16 - Last updated in NVD database

Technical Details for CVE-2026-92025

Vulnerability Analysis

CVE-2026-92025 is a use-after-free condition in the DOM: Navigation component. Use-after-free flaws occur when a program continues to reference memory after it has been released back to the allocator. When the freed memory is reallocated for another object, subsequent access through the stale pointer can corrupt program state.

In browser engines, navigation-related objects manage lifecycle transitions between documents, history entries, and browsing contexts. A mismanaged reference during these transitions can leave dangling pointers accessible from script-reachable code paths. Attackers who control web content can influence allocation and reference patterns to trigger the freed-memory access.

Root Cause

The root cause is improper lifetime management of an object within the DOM navigation code path. Details of the underlying object and reference chain are tracked in Mozilla Bug Report #2068361, which remains access-restricted at the time of publication.

Attack Vector

Exploitation requires a victim to load attacker-controlled web content in an affected version of Firefox or Thunderbird. Thunderbird is affected because it embeds the same Gecko rendering engine, though remote content is disabled by default in email. A crafted page can allocate and free navigation-related objects to place a controlled payload into the freed slot, then trigger the stale reference.

Refer to Mozilla advisories MFSA-2026-90 through MFSA-2026-96 for vendor guidance on affected builds.

Detection Methods for CVE-2026-92025

Indicators of Compromise

Unexpected crashes of firefox.exe, firefox-bin, or thunderbird processes with signatures consistent with heap corruption or access violations in DOM navigation code.
Spawning of child processes or shell interpreters from the browser or mail client process tree following the rendering of untrusted content.
Outbound network connections initiated by the browser process to previously unseen infrastructure shortly after visiting a suspicious page.

Detection Strategies

Inventory installed Firefox and Thunderbird versions across the fleet and flag hosts running builds earlier than the fixed releases listed in the Mozilla advisories.
Correlate browser crash telemetry with URL history to identify pages that trigger repeated faults in navigation components.
Monitor for post-exploitation behaviors such as credential access, LSASS interaction, or persistence mechanisms originating from browser processes.

Monitoring Recommendations

Enable endpoint telemetry for process creation, module loads, and memory-region protection changes within browser processes.
Ingest browser crash reports into a centralized logging platform for trend analysis.
Alert on browser processes writing executable content to disk or modifying autorun locations.

How to Mitigate CVE-2026-92025

Immediate Actions Required

Upgrade Firefox to version 156 or the applicable ESR release (115.41, 140.16, or 153.3).
Upgrade Thunderbird to version 156, 140.16, or 153.3 depending on the deployed branch.
Prioritize patching for endpoints used for general web browsing, developer workstations, and executives.

Patch Information

Mozilla released fixes in Firefox 156, Firefox ESR 115.41, Firefox ESR 140.16, Firefox ESR 153.3, Thunderbird 156, Thunderbird 140.16, and Thunderbird 153.3. Consult MFSA-2026-90, MFSA-2026-91, MFSA-2026-92, MFSA-2026-93, MFSA-2026-94, MFSA-2026-95, and MFSA-2026-96 for the specific advisory tied to each build channel.

Workarounds

Restrict browsing to trusted destinations using enterprise web filtering until patching completes.
Keep the Thunderbird default setting that blocks remote content in messages to reduce exposure via email.
Deploy centrally managed browser update policies to enforce the patched versions across managed endpoints.

bash

# Configuration example
# Verify installed Firefox version on Linux endpoints
firefox --version

# Verify installed Thunderbird version
thunderbird --version

# Windows: query installed version via registry
reg query "HKLM\SOFTWARE\Mozilla\Mozilla Firefox" /v CurrentVersion