CVE-2026-109757 Mozilla CVE debrief

Who should care

Mozilla Firefox users, particularly those with exposure to the Networking component, should assess and prioritize patching or mitigating CVE-2026-109757. Users should review the supplied official advisory or CVE record to validate affected scope, severity, and vendor guidance. Defenders should plan vendor-supported updates or mitigations through normal change control where exposure is confirmed.

Why it matters

CVE-2026-109757 is a sandbox escape vulnerability in Mozilla Firefox's Networking component. Defenders should verify exposure, prioritize patching, and monitor for potential sandbox escape attempts.

• Potential sandbox escape and unauthorized access
• Need to verify exposure and patch or mitigate the vulnerability
• Priority for Firefox users to update to fixed versions

Technical summary

CVE-2026-109757 is a sandbox escape vulnerability in the Networking component of Mozilla Firefox due to a race condition. The vulnerability was fixed in Firefox 158 and Firefox ESR 153.5. This vulnerability allows for a sandbox escape and unauthorized access. Defenders should verify exposure and prioritize patching or mitigating the vulnerability. The vulnerability affects Mozilla Firefox users, particularly those with exposure to the Networking component. Users should assess and prioritize patching or mitigating CVE-2026-109757.

Defensive priority

Patch or verify exposure for Firefox users

Recommended defensive actions

• Patch Firefox to version 158 or Firefox ESR to version 153.5
• Verify exposure for Firefox users
• Monitor for potential sandbox escape 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 Mozilla advisories provide details on the vulnerability and fixed versions. The vulnerability allows for a sandbox escape due to a race condition in the Networking component of Mozilla Firefox. Defenders should verify exposure and prioritize patching or mitigating CVE-2026-109757. The CVE Program record and NIST NVD vulnerability detail provide additional information on the vulnerability.

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.