CVE-2026-109715 Mozilla CVE debrief

Who should care

Mozilla Firefox users, particularly those using versions prior to the patched versions, should assess exposure and prioritize remediation. This includes users of Firefox, Firefox ESR, and other related products that may be affected by the vulnerability. Defenders should review their current versions to determine potential exposure and apply patches or mitigating controls accordingly. Additionally, security teams and vulnerability management teams should be

Why it matters

CVE-2026-109715 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 can be exploited by attackers to potentially execute arbitrary code or cause a denial-of-service condition. Defenders should prioritize verifying Firefox versions and applying patches or mitigating controls to prevent exploitation. The vulnerability has a high impact on Firefox users who have not updated to the patched versions.

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. 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, but additional verification is needed to confirm affected scope and severity.

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.