| Name | CVE-2026-8959 |
| Description | Sandbox escape due to incorrect boundary conditions in the Widget: Win32 component. This vulnerability was fixed in Firefox 151, Firefox ESR 140.11, Thunderbird 151, and Thunderbird 140.11. |
| Source | CVE (at NVD; CERT, ENISA, LWN, oss-sec, fulldisc, Debian ELTS, Red Hat, Ubuntu, Gentoo, SUSE bugzilla/CVE, GitHub advisories/code/issues, web search, more) |
Vulnerable and fixed packages
The table below lists information on source packages.
| Source Package | Release | Version | Status |
|---|
| firefox (PTS) | sid | 151.0-1 | fixed |
| firefox-esr (PTS) | bullseye | 115.14.0esr-1~deb11u1 | fixed |
| bullseye (security) | 140.11.0esr-1~deb11u1 | fixed |
| bookworm | 140.10.2esr-1~deb12u1 | fixed |
| bookworm (security) | 140.11.0esr-1~deb12u1 | fixed |
| trixie | 140.10.2esr-1~deb13u1 | fixed |
| trixie (security) | 140.11.0esr-1~deb13u1 | fixed |
| forky | 140.10.2esr-1 | fixed |
| sid | 140.11.0esr-1 | fixed |
| thunderbird (PTS) | bullseye | 1:115.12.0-1~deb11u1 | fixed |
| bullseye (security) | 1:140.11.0esr-1~deb11u1 | fixed |
| bookworm | 1:140.10.1esr-1~deb12u1 | fixed |
| bookworm (security) | 1:140.10.2esr-1~deb12u1 | fixed |
| trixie | 1:140.10.1esr-1~deb13u1 | fixed |
| trixie (security) | 1:140.10.2esr-1~deb13u1 | fixed |
| forky | 1:140.10.2esr-1 | fixed |
| sid | 1:140.11.0esr-1 | fixed |
The information below is based on the following data on fixed versions.
| Package | Type | Release | Fixed Version | Urgency | Origin | Debian Bugs |
|---|
| firefox | source | (unstable) | (not affected) | | | |
| firefox-esr | source | (unstable) | (not affected) | | | |
| thunderbird | source | (unstable) | (not affected) | | | |
Notes
- firefox <not-affected> (Only affects Firefox on Windows)
- firefox-esr <not-affected> (Only affects Firefox ESR on Windows)
- thunderbird <not-affected> (Only affects Thunderbird on Windows)
https://www.mozilla.org/en-US/security/advisories/mfsa2026-46/#CVE-2026-8959
https://www.mozilla.org/en-US/security/advisories/mfsa2026-48/#CVE-2026-8959
https://www.mozilla.org/en-US/security/advisories/mfsa2026-51/#CVE-2026-8959