CVE-2026-109716 Mozilla CVE debrief

Who should care

Mozilla Firefox users, particularly those using versions prior to the patched versions, should assess exposure and prioritize remediation or compensating controls. This vulnerability affects users of Mozilla Firefox, particularly those using versions prior to the patched versions. Defenders should verify if their deployments use affected versions and prioritize remediation or compensating controls.

Why it matters

CVE-2026-109716 is a vulnerability in the JavaScript Engine component of Mozilla Firefox. It was fixed in Firefox 158, Firefox ESR 115.43, and Firefox ESR 153.5. Defenders should verify if their deployments use affected versions and prioritize remediation or compensating controls.

• Verify Firefox versions to determine potential exposure
• Apply patches or mitigating controls to prevent exploitation
• Monitor for potential exploitation attempts

Technical summary

The vulnerability is caused by incorrect boundary conditions in the JavaScript Engine component of Mozilla Firefox. It was fixed in Firefox 158, Firefox ESR 115.43, and Firefox ESR 153.5. This vulnerability affects users of Mozilla Firefox, particularly those using versions prior to the patched versions. The vulnerability was caused by incorrect boundary conditions in the JavaScript Engine component, which can lead to potential exploitation attempts. Defenders should prioritize verifying Firefox versions and applying patches or mitigating controls.

Defensive priority

Defenders should prioritize verifying Firefox versions and applying patches or mitigating controls.

Recommended defensive actions

• Verify Firefox versions in use and compare to affected versions
• Apply patches or mitigating controls for vulnerable versions
• 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 and source item provide details on the vulnerability and affected versions. However, the CVSS score and severity are not provided. The vulnerability was fixed in Firefox 158, Firefox ESR 115.43, and Firefox ESR 153.5. Defenders should verify if their deployments use affected versions and prioritize remediation or compensating controls. The source item provides details on the vulnerability and affected versions.

Sources and 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.