CVE-2026-16387: Vulnerability in Mozilla Firefox
CVE-2026-16387 is a site isolation vulnerability in the Networking component of Mozilla Firefox. This issue was addressed and fixed in Firefox 153 and Firefox ESR 140.13. The vulnerability has a critical CVSS score of 9.8, indicating high severity with potential for remote exploitation without user interaction. Multiple related vulnerabilities affecting Firefox and Thunderbird were fixed in these versions. There are no confirmed exploits in the wild for this specific issue. The vendor advisory confirms the availability of an official fix.
AI Analysis
Technical Summary
CVE-2026-16387 is a site isolation issue in the Networking component of Mozilla Firefox that could allow security boundaries to be bypassed. This vulnerability was fixed in Firefox 153 and Firefox ESR 140.13. The CVSS 3.1 score is 9.8 (AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H), indicating it is remotely exploitable without privileges or user interaction and can lead to high impact on confidentiality, integrity, and availability. Mozilla's security advisories for Firefox 153 and ESR 140.13 include this fix among multiple other critical and high-impact vulnerabilities. No known exploits in the wild have been reported for this specific vulnerability.
Potential Impact
The vulnerability allows an attacker to bypass site isolation protections in the Networking component, potentially leading to full compromise of confidentiality, integrity, and availability of affected Firefox instances. Given the CVSS score of 9.8, successful exploitation could allow remote attackers to execute arbitrary code or access sensitive information without user interaction or privileges.
Mitigation Recommendations
An official fix is available and has been released by Mozilla in Firefox 153 and Firefox ESR 140.13. Users and administrators should update affected Firefox installations to these versions or later to remediate this vulnerability. No additional mitigation steps are required beyond applying the official update.
CVE-2026-16387: Vulnerability in Mozilla Firefox
Description
CVE-2026-16387 is a site isolation vulnerability in the Networking component of Mozilla Firefox. This issue was addressed and fixed in Firefox 153 and Firefox ESR 140.13. The vulnerability has a critical CVSS score of 9.8, indicating high severity with potential for remote exploitation without user interaction. Multiple related vulnerabilities affecting Firefox and Thunderbird were fixed in these versions. There are no confirmed exploits in the wild for this specific issue. The vendor advisory confirms the availability of an official fix.
CVSS v3.1
Score 9.8critical
Affected software
pkg:github/mozilla/firefox-esrRun on your own infrastructure? Check whether these packages are installed with threat-finder — our free open-source scanner.
AI-Powered Analysis
Machine-generated threat intelligence
Technical Analysis
CVE-2026-16387 is a site isolation issue in the Networking component of Mozilla Firefox that could allow security boundaries to be bypassed. This vulnerability was fixed in Firefox 153 and Firefox ESR 140.13. The CVSS 3.1 score is 9.8 (AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H), indicating it is remotely exploitable without privileges or user interaction and can lead to high impact on confidentiality, integrity, and availability. Mozilla's security advisories for Firefox 153 and ESR 140.13 include this fix among multiple other critical and high-impact vulnerabilities. No known exploits in the wild have been reported for this specific vulnerability.
Potential Impact
The vulnerability allows an attacker to bypass site isolation protections in the Networking component, potentially leading to full compromise of confidentiality, integrity, and availability of affected Firefox instances. Given the CVSS score of 9.8, successful exploitation could allow remote attackers to execute arbitrary code or access sensitive information without user interaction or privileges.
Mitigation Recommendations
An official fix is available and has been released by Mozilla in Firefox 153 and Firefox ESR 140.13. Users and administrators should update affected Firefox installations to these versions or later to remediate this vulnerability. No additional mitigation steps are required beyond applying the official update.
Technical Details
- Data Version
- 5.2
- Assigner Short Name
- mozilla
- Date Reserved
- 2026-07-20T21:57:05.138Z
- Cvss Version
- null
- State
- PUBLISHED
- Remediation Level
- null
- Vendor Advisory Urls
- [{"url":"https://www.mozilla.org/security/advisories/mfsa2026-68/","vendor":"Mozilla"},{"url":"https://www.mozilla.org/security/advisories/mfsa2026-70/","vendor":"Mozilla"}]
Threat ID: 6a5f6cbe2a4a8d5989262605
Added to database: 07/21/2026, 12:57:34 UTC
Last enriched: 07/30/2026, 10:22:45 UTC
Last updated: 09/02/2026, 22:52:09 UTC
Views: 87
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