PatchSiren cyber security CVE debrief
CVE-2026-16355 Mozilla CVE debrief
A critical vulnerability, CVE-2026-16355, was found in the JavaScript Engine's JIT component. This issue was fixed in Firefox 153, Firefox ESR 115.38, Firefox ESR 140.13, Thunderbird 153, and Thunderbird 140.13. The vulnerability is caused by a JIT miscompilation in the JavaScript Engine, which could lead to potential code execution. Users and administrators of Firefox, Firefox ESR, and Thunderbird should apply the updates to prevent potential code execution.
- Vendor
- Mozilla
- Product
- Firefox
- CVSS
- CRITICAL 9.8
- 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 and administrators of Firefox, Firefox ESR, and Thunderbird should apply the updates to prevent potential code execution. This vulnerability could impact users who have not updated their installations to the latest versions.
Technical summary
The CVE-2026-16355 vulnerability, caused by a JIT miscompilation in the JavaScript Engine, has been addressed in Firefox 153, Firefox ESR 115.38, Firefox ESR 140.13, Thunderbird 153, and Thunderbird 140.13. This issue could lead to potential code execution if exploited. Users and administrators of Firefox, Firefox ESR, and Thunderbird should apply the updates to prevent potential code execution. The vulnerability affects users who have not updated their installations to the latest versions. Further verification is recommended to ensure accuracy, and users should review compensating controls for exposed systems while remediation is scheduled and verified.
Defensive priority
High
Recommended defensive actions
- Apply the security updates for Firefox, Firefox ESR, and Thunderbird.
- Ensure all users have the latest versions installed.
- Monitor for any suspicious activity related to JavaScript Engine exploitation.
- 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.
- Confirm whether affected product deployments exist in managed environments and assign an owner for follow-up.
Evidence notes
The CVE record was published on 2026-07-21T13:17:04.000Z and was last modified on 2026-07-22T20:16:50.783Z. The NVD entry is currently Undergoing Analysis. This information is based on the CVE record and NVD details. Further verification is recommended to ensure accuracy.
Official resources
AI-assisted PatchSiren debrief based on the supplied source corpus. The CVE record was published on 2026-07-21T13:17:04.000Z and has not been modified since then. The NVD entry is currently Undergoing Analysis.