CVE-2026-92014: Firefox Graphics Privilege Escalation Flaw

CVE-2026-92014 Overview

CVE-2026-92014 is a privilege escalation vulnerability caused by incorrect boundary conditions in the Graphics component of Mozilla Firefox and Thunderbird. The flaw is tracked under CWE-120 (Classic Buffer Copy without Checking Size of Input). Mozilla addressed the issue in Firefox ESR 115.41, Firefox ESR 140.16, and Thunderbird 140.16. Successful exploitation requires user interaction, such as visiting a crafted web page or opening malicious content, and can lead to elevated privileges within the affected application.

Critical Impact
An attacker who convinces a user to load malicious graphics content can escalate privileges and compromise confidentiality, integrity, and availability of the affected browser or mail client.

Affected Products

Mozilla Firefox ESR versions prior to 115.41
Mozilla Firefox ESR versions prior to 140.16
Mozilla Thunderbird versions prior to 140.16

Discovery Timeline

2026-09-15 - CVE-2026-92014 published to the National Vulnerability Database
2026-09-16 - Last updated in NVD database

Technical Details for CVE-2026-92014

Vulnerability Analysis

The vulnerability resides in the Graphics component shared across Firefox and Thunderbird. Incorrect boundary conditions during graphics processing allow memory operations to exceed intended limits. This weakness is classified under CWE-120, which covers buffer copies performed without validating input size.

Exploitation requires user interaction, meaning an attacker must lure the target into rendering malicious content. Because the affected code runs within the browser or mail client process, a successful attack can escalate privileges beyond the sandbox boundaries typically enforced by these applications. The EPSS probability of exploitation stands at 0.255%.

Mozilla published details across advisories MFSA-2026-91, MFSA-2026-92, and MFSA-2026-95.

Root Cause

The defect stems from incorrect boundary checks in graphics rendering logic. When the component processes attacker-controlled dimensions or offsets, computations produce values that fall outside the expected safe range. Downstream memory operations then read or write beyond the allocated buffer, enabling corruption of adjacent structures used by higher-privileged code paths within the application.

Attack Vector

The attack vector is network-based and requires user interaction. An attacker hosts a malicious web page or crafts email content that references graphics data designed to trigger the boundary miscalculation. When Firefox renders the page or Thunderbird processes the message content, the vulnerable code path executes and enables privilege escalation within the application context. Full technical details are documented in Mozilla Bug Report #2060000.

Detection Methods for CVE-2026-92014

Indicators of Compromise

Unexpected crashes or memory access violations in firefox.exe or thunderbird.exe processes tied to graphics rendering modules.
Child processes spawned by Firefox or Thunderbird that deviate from normal browser or mail client behavior.
Outbound network connections from browser or mail processes to unfamiliar domains shortly after rendering third-party content.

Detection Strategies

Inventory endpoints running Firefox ESR and Thunderbird and flag versions below 115.41, 140.16, and 140.16 respectively.
Monitor for anomalous memory allocations and access violations in the Mozilla Graphics component using endpoint detection telemetry.
Correlate crash telemetry with web browsing history to identify pages that consistently trigger faults in vulnerable versions.

Monitoring Recommendations

Enable browser crash reporting and forward telemetry to a centralized logging platform for review.
Track process lineage from firefox.exe and thunderbird.exe to detect unexpected child processes or code execution.
Alert on outbound connections initiated by browser or mail processes to newly registered or low-reputation domains.

How to Mitigate CVE-2026-92014

Immediate Actions Required

Upgrade Firefox ESR to version 115.41 or 140.16, and Thunderbird to version 140.16.
Prioritize patching endpoints used by privileged users, developers, and email-facing administrators.
Verify installed versions across managed endpoints and enforce automatic update policies where possible.

Patch Information

Mozilla released fixes in Firefox ESR 115.41, Firefox ESR 140.16, and Thunderbird 140.16. Patch details are available in MFSA-2026-91, MFSA-2026-92, and MFSA-2026-95. Administrators should validate deployment through enterprise update channels or configuration management tools.

Workarounds

Restrict rendering of untrusted content by enforcing enterprise policies that block unknown script sources and remote images in Thunderbird.
Deploy application allowlists that prevent Firefox and Thunderbird from launching unexpected child processes.
Educate users to avoid opening unsolicited links or email attachments until patches are applied across the environment.

bash

# Verify installed Firefox and Thunderbird versions on Linux endpoints
firefox --version
thunderbird --version