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CVE-2026-16390 Mozilla CVE debrief

A mitigation bypass vulnerability was discovered in the Enterprise Policies component of Firefox, Firefox ESR, and Thunderbird. This issue allows attackers to bypass existing mitigations, potentially leading to arbitrary code execution or other malicious activities. The vulnerability was addressed in Firefox 153, Firefox ESR 140.13, Thunderbird 153, and Thunderbird 140.13. Organizations should review their current configurations and update to the latest versions to prevent potential exploitation.

Vendor
Mozilla
Product
Firefox
CVSS
CRITICAL 9.1
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

Organizations using Firefox, Firefox ESR, or Thunderbird with the Enterprise Policies component enabled should prioritize patching to prevent potential exploitation. Additionally, security teams and vulnerability management teams should review the affected systems and plan for updates or mitigations.

Technical summary

The CVE-2026-16390 vulnerability is a critical mitigation bypass issue in the Enterprise Policies component of Firefox, Firefox ESR, and Thunderbird. It was fixed in Firefox 153, Firefox ESR 140.13, Thunderbird 153, and Thunderbird 140.13. The CVSS score is 9.1, indicating a high severity level. This vulnerability could allow attackers to bypass existing security measures, potentially leading to unauthorized access or malicious activities.

Defensive priority

High priority should be given to patching affected systems due to the critical severity of the vulnerability.

Recommended defensive actions

  • Apply patches for Firefox 153, Firefox ESR 140.13, Thunderbird 153, and Thunderbird 140.13
  • Review and update Enterprise Policies component configurations
  • Monitor for potential exploitation attempts
  • 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 2026-07-21T13:17:14.160Z and last modified on 2026-07-22T20:16:57.073Z. The NVD entry is currently Undergoing Analysis. This information is based on the CVE.org and NVD sources. Further verification is recommended to confirm affected scope and severity.

Sources and references

Verified primary and authoritative sources

  • CVE-2026-16390 CVE Program record

    Publisher, destination, and source semantics verified

    URL: https://www.cve.org/CVERecord?id=CVE-2026-16390

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

  • CVE-2026-16390 NVD vulnerability detail

    Publisher, destination, and source semantics verified

    URL: https://nvd.nist.gov/vuln/detail/CVE-2026-16390

    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.