Description
Same-origin policy bypass in the Networking: DNS component. This vulnerability was fixed in Firefox 153, Firefox ESR 140.13, Thunderbird 153, and Thunderbird 140.13.
Published: 2026-07-21
Score: 9.1 Critical
EPSS: < 1% Very Low
KEV: No
Impact: n/a
Action: n/a
AI Analysis

Impact

An flaw in the Networking: DNS component lets a user bypass the browser’s same‑origin policy, granting access to DNS responses that should otherwise be restricted. This weakness is identified as CWE‑346.

Affected Systems

Both Mozilla Firefox and Thunderbird disclose this vulnerability in versions released before the immediate fixes, which are Firefox 153, Firefox ESR 140.13, Thunderbird 153, and Thunderbird 140.13. Users of earlier releases remain vulnerable.

Risk and Exploitability

The CVSS score of 9.1 marks it as critical. By the EPSS score of less than 1 %, the likelihood of exploitation is low. It is not listed in the CISA KEV catalog. Based on the description, it is inferred that an attacker might leverage malicious DNS responses to trigger the bypass when a victim’s browser processes those replies.

Generated by OpenCVE AI on August 4, 2026 at 05:42 UTC.

Remediation

No vendor fix or workaround currently provided.

OpenCVE Recommended Actions

  • Upgrade to Firefox 153 or newer, or the ESR 140.13 release, or upgrade Thunderbird to 153 or newer, or the ESR 140.13 release to address the flaw.
  • Because no official workaround is provided, temporarily mitigate risk by disabling DNS prefetch or related features that rely on the vulnerable component, if possible in configuration settings.
  • Enable automatic updates and monitor Mozilla security advisories for any future advice or updates.

Generated by OpenCVE AI on August 4, 2026 at 05:42 UTC.

Tracking

Sign in to view the affected projects.

Advisories
Source ID Title
Debian DLA Debian DLA DLA-4695-1 firefox-esr security update
Debian DLA Debian DLA DLA-4727-1 thunderbird security update
Debian DSA Debian DSA DSA-6394-1 firefox-esr security update
Debian DSA Debian DSA DSA-6418-1 thunderbird security update
History

Fri, 24 Jul 2026 00:30:00 +0000

Type Values Removed Values Added
References
Metrics threat_severity

None

 threat_severity

Moderate

Wed, 22 Jul 2026 20:00:00 +0000

Type Values Removed Values Added
Description Same-origin policy bypass in the Networking: DNS component. This vulnerability was fixed in Firefox 153 and Firefox ESR 140.13. Same-origin policy bypass in the Networking: DNS component. This vulnerability was fixed in Firefox 153, Firefox ESR 140.13, Thunderbird 153, and Thunderbird 140.13.
References

Wed, 22 Jul 2026 18:30:00 +0000

Type Values Removed Values Added
Weaknesses CWE-346
Metrics cvssV3_1

{'score': 9.1, 'vector': 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N'}

ssvc

{'options': {'Automatable': 'yes', 'Exploitation': 'none', 'Technical Impact': 'total'}, 'version': '2.0.3'}

Wed, 22 Jul 2026 04:00:00 +0000

Type Values Removed Values Added
First Time appeared Mozilla
Mozilla firefox
Vendors & Products Mozilla
Mozilla firefox

Tue, 21 Jul 2026 12:45:00 +0000

Type Values Removed Values Added
Description Same-origin policy bypass in the Networking: DNS component. This vulnerability was fixed in Firefox 153 and Firefox ESR 140.13.
Title Same-origin policy bypass in the Networking: DNS component
References

Subscriptions

Mozilla Firefox Thunderbird
cve-icon MITRE

Status: PUBLISHED

Assigner: mozilla

Published:

Updated: 2026-07-22T19:18:44.571Z

Reserved: 2026-07-20T21:56:51.463Z

Link: CVE-2026-16381

cve-icon Vulnrichment

Updated: 2026-07-22T17:11:17.558Z

cve-icon NVD

Status : Analyzed

Published: 2026-07-21T13:17:13.260

Modified: 2026-07-24T15:19:11.863

Link: CVE-2026-16381

cve-icon Redhat

Severity : Moderate

Publid Date: 2026-07-21T12:37:56Z

Links: CVE-2026-16381 - Bugzilla

cve-icon OpenCVE Enrichment

Updated: 2026-08-04T05:45:03Z

Weaknesses