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CVE-2026-92021 Mozilla CVE debrief

A use-after-free vulnerability in the JavaScript Engine's JIT component was fixed in Firefox ESR 140.16 and Thunderbird 140.16. This vulnerability could potentially allow for code execution on affected systems. Defenders should assess exposure, particularly for systems using these products, and prioritize updating to the fixed versions. The vulnerability was reported by [email protected] and fixed in Firefox ESR 140.16 and Thunderbird 140.16. It is a high-severity issue, with a CVSS score of 8.8, and defenders should take immediate action to update affected systems.

Vendor
Mozilla
Product
Firefox
CVSS
HIGH 8.8
CISA KEV
Not listed in stored evidence
Original CVE published
2026-09-15
Original CVE updated
2026-09-20
Advisory published
2026-09-15
Advisory updated
2026-09-20

Who should care

Defenders responsible for systems using Firefox ESR and Thunderbird should assess exposure and prioritize updating to version 140.16. This includes operators, platform administrators, vulnerability management teams, and security teams. The vulnerability's high severity and potential for code execution make it a priority for defenders to take action.

Why it matters

A use-after-free vulnerability in the JavaScript Engine's JIT component was fixed in Firefox ESR 140.16 and Thunderbird 140.16. Defenders should assess exposure, particularly for systems using these products, and prioritize updating to the fixed versions.

  • Potential code execution on affected systems
  • Required verification of system exposure and software versions
  • Priority for updating Firefox ESR and Thunderbird to version 140.16

Technical summary

The vulnerability is a use-after-free in the JavaScript Engine's JIT component. It was fixed in Firefox ESR 140.16 and Thunderbird 140.16. This type of vulnerability could potentially allow for code execution on affected systems. Defenders should assess exposure and prioritize updating to the fixed versions. The issue has a high CVSS score of 8.8, indicating a high severity.

Defensive priority

High priority for updating Firefox ESR and Thunderbird to version 140.16.

Recommended defensive actions

  • Update Firefox ESR to version 140.16
  • Update Thunderbird to version 140.16
  • Assess exposure for systems using Firefox ESR and Thunderbird

Evidence notes

The vulnerability was reported by [email protected] and fixed in Firefox ESR 140.16 and Thunderbird 140.16. The issue is a use-after-free vulnerability in the JavaScript Engine's JIT component. Defenders should verify system exposure and software versions, and prioritize updating to the fixed versions. The CVE record was published on 2026-09-15T13:16:52.210Z and has not been modified since then.

Sources and references

Verified primary and authoritative sources

  • CVE-2026-92021 CVE Program record

    Publisher, destination, and source semantics verified

    URL: https://www.cve.org/CVERecord?id=CVE-2026-92021

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

  • CVE-2026-92021 NVD vulnerability detail

    Publisher, destination, and source semantics verified

    URL: https://nvd.nist.gov/vuln/detail/CVE-2026-92021

    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.