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9.6
CVE-2026-109707: Firefox and Thunderbird can escape sandbox
CVE-2026-109707 · published 2 days ago
Summary
The standard Firefox, Firefox ESR, and Thunderbird browsers on Debian have a flaw that could let a malicious webpage break out of the browser's protective sandbox and affect the rest of the computer. This could allow an attacker to run code with your user’s privileges. Install the latest versions (Firefox 158, Firefox ESR 153.5, Thunderbird 158 or 153.5) to fix the problem.
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
DEBIAN-CVE-2026-109707
Sandbox escape due to use-after-free 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=2059150
- https://www.mozilla.org/security/advisories/mfsa2026-106/
- https://www.mozilla.org/security/advisories/mfsa2026-108/
- https://security-tracker.debian.org/tracker/CVE-2026-109707 Vendor Advisory
- https://www.mozilla.org/security/advisories/mfsa2026-109/
- https://www.mozilla.org/security/advisories/mfsa2026-110/
Severity
9.6
Critical
Type
CWE-416Use After Free
Timeline
Published13 Oct 2026
Updated15 Oct 2026
First seen13 Oct 2026
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