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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.

Sources and references

Verified primary and authoritative sources

  • CVE-2026-16355 CVE Program record

    Publisher, destination, and source semantics verified

    URL: https://www.cve.org/CVERecord?id=CVE-2026-16355

    CVE Program - Official CVE Program record with source-provided CVE metadata.

  • CVE-2026-16355 NVD vulnerability detail

    Publisher, destination, and source semantics verified

    URL: https://nvd.nist.gov/vuln/detail/CVE-2026-16355

    NIST National Vulnerability Database - Official NIST NVD detail page and source-specific vulnerability assessment.

Supplemental references

Methodology and review provenance

AI-assisted synthesis based on stored public vulnerability evidence. System validation, approval state, and publication status do not by themselves establish human review of this revision. PatchSiren helps prioritize defensive review and does not prove exposure or remediation on any system.