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9.6
CVE-2026-109708: Firefox and Thunderbird could let malicious code leave sandbox
CVE-2026-109708 · published 2 days ago
Summary
The networking part of Firefox and Thunderbird may allow harmful code to break out of its safe container. This could let an attacker affect other parts of the system. Install the latest Firefox (158 or newer) and Thunderbird (158 or newer) versions, or the corresponding ESR updates, to fix the issue.
What to do
The CVE record does not list a fixed version. Check the vendor's site or the advisory links below - a fix may already be released.
Affected software
| Ecosystem | Vendor | Product | Affected versions |
|---|---|---|---|
| – | mozilla | firefox | All versions |
| Debian:12 | debian | firefox-esr | All versions |
| – | mozilla | thunderbird | All versions |
Original advisory text
Sandbox escape due to incorrect boundary conditions in the Networking component
Sandbox escape due to incorrect boundary conditions in the Networking component. This vulnerability was fixed in Firefox 158, Firefox ESR 153.5, Thunderbird 158, and Thunderbird 153.5.
References
- https://bugzilla.mozilla.org/show_bug.cgi?id=2059151
- https://www.mozilla.org/security/advisories/mfsa2026-106/
- https://www.mozilla.org/security/advisories/mfsa2026-108/
- https://security-tracker.debian.org/tracker/CVE-2026-109708 Vendor Advisory
- https://www.mozilla.org/security/advisories/mfsa2026-109/
- https://www.mozilla.org/security/advisories/mfsa2026-110/
Severity
9.6
Critical
Type
CWE-119Buffer Overflow
Timeline
Published13 Oct 2026
Updated15 Oct 2026
First seen13 Oct 2026
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