CVE-2026-109751 Mozilla CVE debrief

Who should care

Defenders responsible for managing Firefox installations, particularly those using versions prior to 158 or Firefox ESR versions prior to 153.5, should assess exposure and apply patches.

Why it matters

CVE-2026-109751 is an information disclosure vulnerability in Firefox's Networking component. Defenders should verify exposure, apply patches, and monitor for potential exploitation attempts. The vulnerability was fixed in Firefox 158 and Firefox ESR 153.5.

• Verify exposure of Firefox installations to potential information disclosure
• Assess and apply patches for vulnerable Firefox versions
• Monitor for potential exploitation attempts targeting the Networking component

Technical summary

The vulnerability, CVE-2026-109751, is an information disclosure issue in the Networking component of Firefox. It was fixed in Firefox 158 and Firefox ESR 153.5. The CVE record and Mozilla's advisory confirm the vulnerability, which could allow attackers to access sensitive information processed by the Networking component. Defenders should prioritize verifying exposure and applying patches for Firefox versions prior to 158 or Firefox ESR versions prior to 153.5. Technical details are limited to publicly available information from the CVE record and Mozilla's advisory.

Defensive priority

Defenders should prioritize verifying exposure and applying patches for Firefox versions prior to 158 or Firefox ESR versions prior to 153.5.

Recommended defensive actions

• Verify Firefox version and update to 158 or Firefox ESR 153.5 if necessary
• Review system inventory for affected Firefox installations
• Apply patches or updates as recommended by Mozilla
• Monitor for potential exploitation attempts targeting the Networking component
• 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

Evidence notes

The CVE record and Mozilla's advisory confirm the information disclosure vulnerability in the Networking component of Firefox. The vulnerability was fixed in Firefox 158 and Firefox ESR 153.5. Evidence is limited to public CVE and Mozilla advisory information. Defenders should verify exposure using official advisories and apply patches for Firefox versions prior to 158 or Firefox ESR versions prior to 153.5. Additional verification steps may be necessary based on specific deployment contexts.

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.