CVE-2026-16374: Mozilla Firefox Information Disclosure

CVE-2026-16374 Overview

CVE-2026-16374 is an information disclosure vulnerability affecting the Framework component within Mozilla DevTools. The flaw allows a remote attacker to obtain sensitive information from affected Firefox and Thunderbird builds without authentication or user interaction. Mozilla addressed the issue in Firefox 153, Firefox ESR 140.13, Thunderbird 153, and Thunderbird 140.13. The vulnerability is tracked under [CWE-200] (Exposure of Sensitive Information to an Unauthorized Actor).

Critical Impact
A network-based attacker can leverage the DevTools Framework flaw to read data intended to remain confidential, without requiring privileges or user interaction.

Affected Products

Mozilla Firefox versions prior to 153
Mozilla Firefox ESR versions prior to 140.13
Mozilla Thunderbird versions prior to 153 and prior to 140.13

Discovery Timeline

2026-07-21 - CVE-2026-16374 published to NVD
2026-07-22 - Last updated in NVD database

Technical Details for CVE-2026-16374

Vulnerability Analysis

CVE-2026-16374 is an information disclosure weakness in the Framework component used by Mozilla DevTools. The Framework subsystem provides shared infrastructure for developer tooling such as the debugger, inspector, and console. According to Mozilla's advisories MFSA-2026-68, MFSA-2026-70, MFSA-2026-71, and MFSA-2026-72, the flaw exposes data that should remain confidential to the browser process or to the origin under inspection.

The vulnerability impacts confidentiality only. Integrity and availability of the affected clients are not directly affected. Because the flaw is reachable over the network with no privileges and no user interaction, any content rendered in the browser can act as a trigger surface.

Root Cause

The underlying weakness is classified as [CWE-200]. Mozilla has not published the full technical details of the leaked data path, but the fix landed across the Firefox 153 and ESR 140.13 branches, indicating a shared code path in the DevTools Framework. Further engineering context is tracked in Mozilla Bug Report #2027519, which remains access-restricted at the time of publication.

Attack Vector

Exploitation occurs over the network. An attacker hosts or injects crafted web content that interacts with the DevTools Framework in a way that causes sensitive data to be returned or observable. No authentication is required, and the victim does not need to interact beyond loading attacker-controlled content in a vulnerable client.

No public proof-of-concept exploit code is available. The vulnerability is not listed in the CISA Known Exploited Vulnerabilities catalog, and there are no reports of exploitation in the wild.

// No verified exploitation code is available for CVE-2026-16374.
// Refer to Mozilla advisories MFSA-2026-68, MFSA-2026-70,
// MFSA-2026-71, and MFSA-2026-72 for vendor-supplied details.

Detection Methods for CVE-2026-16374

Indicators of Compromise

No file-based or network-based indicators of compromise have been published for CVE-2026-16374.
Unexpected outbound requests from Firefox or Thunderbird processes to attacker-controlled domains following the rendering of untrusted content.
Presence of Firefox or Thunderbird binaries at versions earlier than Firefox 153, ESR 140.13, or Thunderbird 140.13 / 153 on managed endpoints.

Detection Strategies

Inventory installed browser and mail client versions and flag hosts running builds earlier than the fixed releases.
Correlate browser process telemetry with DNS and HTTP egress to identify anomalous data flows originating from firefox.exe, firefox-bin, or thunderbird processes.
Review endpoint software update logs to confirm that Mozilla auto-update has applied the patched versions on all managed devices.

Monitoring Recommendations

Ingest browser and mail client version telemetry into a central data lake and alert on outdated Mozilla installations.
Monitor for large or unusual outbound payloads from browser processes that could indicate exfiltration of leaked data.
Track vendor advisories MFSA-2026-68, MFSA-2026-70, MFSA-2026-71, and MFSA-2026-72 for any updates or additional guidance.

How to Mitigate CVE-2026-16374

Immediate Actions Required

Upgrade all Firefox installations to version 153 or later.
Upgrade Firefox ESR installations to 140.13 or later.
Upgrade Thunderbird installations to 153 or later, or to 140.13 on the ESR branch.
Verify that automatic updates are enabled on all endpoints running Mozilla products.

Patch Information

Mozilla has published fixes across four security advisories: MFSA-2026-68, MFSA-2026-70, MFSA-2026-71, and MFSA-2026-72. Applying the vendor-supplied updates is the definitive remediation. Enterprises using Firefox ESR should follow the ESR channel rather than downgrading to consumer builds.

Workarounds

No official workaround has been published by Mozilla; patching is the recommended path.
Restrict browsing to trusted domains through proxy or DNS filtering until patches are deployed.
Disable or restrict access to DevTools via enterprise policy (devtools.policy.disabled) where developer tooling is not required.

bash

# Example: enforce Firefox update on managed Linux endpoints
sudo snap refresh firefox
# or, for distribution packages
sudo apt-get update && sudo apt-get install --only-upgrade firefox firefox-esr thunderbird
# Verify installed version meets the fixed release
firefox --version
thunderbird --version