PatchSiren cyber security CVE debrief
CVE-2026-16400 Mozilla CVE debrief
A vulnerability in the DOM: Security component of Firefox and Thunderbird allows for information disclosure. The issue was addressed with the release of Firefox 153 and Thunderbird 153. This vulnerability has a high CVSS score of 7.5, indicating a high severity level. Users of Firefox and Thunderbird should update to versions 153 or later to address this vulnerability. The NVD entry is currently Undergoing Analysis.
- Vendor
- Mozilla
- Product
- Firefox
- CVSS
- HIGH 7.5
- CISA KEV
- Not listed in stored evidence
- Original CVE published
- 2026-07-21
- Original CVE updated
- 2026-07-22
- Advisory published
- 2026-07-21
- Advisory updated
- 2026-07-22
Who should care
Users of Firefox and Thunderbird should update to versions 153 or later to address this vulnerability. This vulnerability has a high CVSS score of 7.5, indicating a high severity level. Security teams and operators should review the vulnerability details and apply necessary updates or mitigations.
Technical summary
A vulnerability in the DOM: Security component of Firefox and Thunderbird allows for information disclosure. The issue was addressed with the release of Firefox 153 and Thunderbird 153. This vulnerability has a high CVSS score of 7.5, indicating a high severity level. The vulnerability was fixed in Firefox 153 and Thunderbird 153. Users should verify their versions and update if necessary. Security teams should review Mozilla's security advisories (MFSA2026-68 and MFSA2026-71) for additional details on the issue and its resolution. Affected product deployments in managed environments should be confirmed and owners assigned for follow-up. Compensating controls for exposed systems should be reviewed while remediation is scheduled and verified. Relevant monitoring, detection, and logs for exposed assets should be checked for extra review.
Defensive priority
High priority due to the high CVSS score of 7.5 and the potential for information disclosure.
Recommended defensive actions
- Update Firefox to version 153 or later
- Update Thunderbird to version 153 or later
- Review and apply security advisories from Mozilla
- Verify Firefox and Thunderbird versions in managed environments
- Review compensating controls for exposed systems while remediation is scheduled and verified
- Check relevant monitoring, detection, and logs for exposed assets that need extra review
- Track exceptions, retest remediated assets, and close the item only after evidence is documented
Evidence notes
The CVE record and NVD entry provide information on the vulnerability, and Mozilla's security advisories (MFSA2026-68 and MFSA2026-71) offer additional details on the issue and its resolution. The vulnerability was fixed in Firefox 153 and Thunderbird 153. Users should verify their versions and update if necessary. The CVE record was published on 2026-07-21T13:17:15.367Z and has been reviewed for accuracy.
Official resources
AI-assisted PatchSiren debrief based on the supplied source corpus. The CVE record was published on 2026-07-21T13:17:15.367Z and has not been modified since then.