Skip to main content
OneCon26: Gain the advantage in the AI era. Oct. 20–22 in Las Vegas.Register Now
Vulnerability Database/CVE-2026-92038

CVE-2026-92038: Firefox Remote Settings Client RCE Vulnerability

CVE-2026-92038 is a remote code execution vulnerability affecting the Remote Settings Client in Firefox and Thunderbird. Attackers can bypass mitigations to execute malicious code. This article covers technical details, affected versions, security impact, and available patches.

Published:

CVE-2026-92038 Overview

CVE-2026-92038 is a mitigation bypass vulnerability in the Remote Settings Client component used by Mozilla Firefox and Thunderbird. The flaw allows an attacker to circumvent security controls enforced through the Remote Settings distribution channel. Mozilla addressed the issue in Firefox 156, Firefox ESR 153.3, Thunderbird 156, and Thunderbird 153.3. The National Vulnerability Database has not published a CVSS score for this issue at the time of writing.

Critical Impact

A successful bypass could weaken protections that Mozilla delivers dynamically through Remote Settings, reducing the effectiveness of downstream security policies enforced by the browser or mail client.

Affected Products

  • Mozilla Firefox versions prior to 156
  • Mozilla Firefox ESR versions prior to 153.3
  • Mozilla Thunderbird versions prior to 156 and prior to 153.3

Discovery Timeline

  • 2026-09-15 - CVE-2026-92038 published to NVD
  • 2026-09-16 - Last updated in NVD database

Technical Details for CVE-2026-92038

Vulnerability Analysis

The Remote Settings Client is the Mozilla component responsible for retrieving and applying dynamically distributed configuration data. This includes safe browsing lists, certificate revocation data, add-on blocklists, and other security-relevant policies. A mitigation bypass in this component means that a protection mechanism enforced through Remote Settings can be evaded under specific conditions.

Mozilla has not published a full technical description of the bypass condition in the public advisories referenced by this CVE. The fix ships as part of the coordinated releases documented in Mozilla Security Advisory MFSA-2026-90, MFSA-2026-93, MFSA-2026-94, and MFSA-2026-96.

Root Cause

The root cause resides in how the Remote Settings Client validates or applies data delivered through the Remote Settings pipeline. Details on the specific validation gap are tracked in Mozilla Bug Report #2068952, which is referenced in the vendor advisories.

Attack Vector

The attack vector for this class of issue typically involves influencing the state or content processed by the Remote Settings Client so that a security control it is expected to enforce is skipped or downgraded. The NVD entry lists no exploit availability, no public proof-of-concept, and no CISA Known Exploited Vulnerabilities listing.

No verified proof-of-concept code is available. See the Mozilla advisories linked above for authoritative technical detail.

Detection Methods for CVE-2026-92038

Indicators of Compromise

  • No public indicators of compromise have been published for CVE-2026-92038.
  • Absence of expected Remote Settings updates or unexpected rollback of blocklist and safebrowsing data on Firefox or Thunderbird endpoints may warrant investigation.

Detection Strategies

  • Inventory Firefox, Firefox ESR, and Thunderbird installations across managed endpoints and compare installed versions against the fixed releases.
  • Alert on browser or mail client versions below Firefox 156, Firefox ESR 153.3, Thunderbird 156, or Thunderbird 153.3.
  • Monitor process telemetry for outdated Mozilla binaries executing on endpoints where automatic updates should have applied.

Monitoring Recommendations

  • Track browser and mail client update compliance through endpoint management tooling.
  • Correlate outbound network activity from Firefox and Thunderbird processes with expected Remote Settings endpoints served by Mozilla.
  • Review software inventory data on a scheduled cadence to catch systems that fail to receive the patched builds.

How to Mitigate CVE-2026-92038

Immediate Actions Required

  • Upgrade Firefox to version 156 or later on all supported platforms.
  • Upgrade Firefox ESR deployments to 153.3 or later.
  • Upgrade Thunderbird installations to 156 or 153.3, matching the deployed release channel.
  • Verify that automatic updates are enabled and functional on managed endpoints.

Patch Information

Mozilla shipped the fix in Firefox 156, Firefox ESR 153.3, Thunderbird 156, and Thunderbird 153.3. Refer to Mozilla Security Advisory MFSA-2026-90, MFSA-2026-93, MFSA-2026-94, and MFSA-2026-96 for release notes and cross-references to Mozilla Bug Report #2068952.

Workarounds

  • Mozilla has not published a supported workaround for CVE-2026-92038; applying the patched release is the recommended remediation.
  • Where immediate patching is not possible, restrict use of affected Firefox and Thunderbird versions in high-risk environments and prioritize accelerated update deployment.
bash
# Verify installed Firefox version on Linux endpoints
firefox --version

# Verify installed Thunderbird version on Linux endpoints
thunderbird --version

Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.

Experience the Most Advanced Cybersecurity Platform

See how the world’s most intelligent, autonomous cybersecurity platform can protect your organization today and into the future.

Try SentinelOne