# CVE-2026-100818

Firefox sandbox escape (Gtk use-after-free) enabling arbitrary code execution.

- Page: https://www.vulneraibility.com/cve/CVE-2026-100818
- CVSS: 9.6
- Known exploited: not in CISA KEV as of our last sync
- EPSS: 0.27% (percentile 18.6)
- CISA SSVC: exploitation none, automatable no, technical impact total (assessed 2026-09-29)
- Weakness: CWE-416
- Published: 2026-09-29

## Affected

- Mozilla Firefox (desktop, Gtk builds)
- Firefox < 157
- Firefox ESR < 153.4
- Firefox ESR 140 < 140.17

## Impact

Escape Firefox sandbox via a Gtk use-after-free to execute arbitrary code as the user from crafted web content.

## Action

Immediate action required

## Recommendation

Update to Firefox 157+ or ESR 153.4/140.17+ immediately.

## References

- [other] https://bugzilla.mozilla.org/show_bug.cgi?id=2069399
- [other] https://www.mozilla.org/security/advisories/mfsa2026-100/
- [other] https://www.mozilla.org/security/advisories/mfsa2026-101/
- [other] https://www.mozilla.org/security/advisories/mfsa2026-102/
- [other] https://www.mozilla.org/security/advisories/mfsa2026-103/
- [other] https://www.mozilla.org/security/advisories/mfsa2026-97/
- [other] https://www.mozilla.org/security/advisories/mfsa2026-99/

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Summary, impact and action are written by the vulneraibility.com AI analysis pipeline from the CVE record, NVD, CISA and FIRST data; verify against the references.