CVE-2026-100801 Mozilla CVE debrief

Who should care

Defenders responsible for Mozilla Firefox and Thunderbird deployments should assess exposure and prioritize patching or mitigating vulnerable installations. This includes operators, platform administrators, vulnerability management teams, and security teams who need to review the vulnerability's impact on their environments and plan accordingly.

Why it matters

CVE-2026-100801 is a high-severity privilege escalation vulnerability in Mozilla Firefox and Thunderbird. Defenders should assess exposure and prioritize patching or mitigating vulnerable installations.

• Verify exposure for Firefox and Thunderbird installations using affected versions
• Patch or mitigate vulnerable installations to prevent privilege escalation

Technical summary

CVE-2026-100801 is a high-severity privilege escalation vulnerability in the DLL Services component of Mozilla Firefox and Thunderbird. The vulnerability was fixed in various versions of Firefox, Thunderbird, and Firefox ESR, including 153.4, 157, 159, and 140.17. Defenders should assess exposure and prioritize patching or mitigating vulnerable installations to prevent privilege escalation. Affected product context and defensive impact should be considered when evaluating this vulnerability. The CVE record and NVD detail page provide information on the vulnerability, including its CVSS score of 8.8 and affected software versions.

Defensive priority

Patch or verify exposure for Firefox and Thunderbird installations using affected versions.

Recommended defensive actions

• Patch Firefox to version 159 or later
• Patch Thunderbird to version 157 or later
• Patch Firefox ESR to version 153.6 or later
• Verify exposure for Firefox and Thunderbird installations using affected versions
• 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 NVD detail page provide information on the vulnerability, including its CVSS score of 8.8 and affected software versions. The official CVE Program record and NIST NVD detail page offer source-provided CVE metadata and source-specific vulnerability assessments. Defenders should review these sources to understand the vulnerability's impact and verify exposure in their deployments.

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.