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CVE-2026-8959Sandbox escape due to incorrect boundary conditions in the Widget: Win32 component
- 9.6CriticalCVSS base score
- 0.42%Exploitation in 30 daysEPSS · top 64% of all CVEs
- NoKnown exploitednot in CISA's KEV catalog
- NonePublic exploitsnone known yet
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.
Timeline
ID reserved
By mozilla
Published
Changes after publication (a new score, a public exploit, EPSS crossing 1, 10 or 50 %, leaving KEV) are kept since November 2026; earlier ones are not known.
Scores
| Scored by | CVSS | Score | Vector |
|---|---|---|---|
| CISA-ADPADP (enrichment) | 3.1 | Critical9.6 | CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:H/A:H |
| NVDNVD · Analyzed | 3.1 | Critical9.6 | CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:H/A:H |
- EPSS (exploitation in 30 days)
- 0.42% · top 64% of all CVEs (13 Nov 2026)
- CISA SSVC
- Exploitation: none · Automatable: no · Technical impact: total
Loading the EPSS history…
The list uses the assigner's score when there is one, then CISA's, then NVD's: Critical 9.6.
Affected products
- unaffected 140.11 – ≤ 140.*
- unaffected 151 – ≤ *
- unaffected 140.11 – ≤ 140.*
- unaffected 151 – ≤ *
References
References5
- https://bugzilla.mozilla.org/show_bug.cgi?id=2034754 (opens in a new tab)
- https://www.mozilla.org/security/advisories/mfsa2026-46/ (opens in a new tab)
- https://www.mozilla.org/security/advisories/mfsa2026-48/ (opens in a new tab)
- https://www.mozilla.org/security/advisories/mfsa2026-50/ (opens in a new tab)
- https://www.mozilla.org/security/advisories/mfsa2026-51/ (opens in a new tab)
Sources
The same CVE in the primary databases and aggregators, to check against.
- CVE.org record (opens in a new tab)
- CVE List JSON (GitHub) (opens in a new tab)
- NVD (opens in a new tab)
- FIRST EPSS (opens in a new tab)
- EUVD EUVD-2026-30910 (opens in a new tab)
- OSV.dev (opens in a new tab)
- GitHub Advisories (opens in a new tab)
- CIRCL Vulnerability-Lookup (opens in a new tab)
Badge for a README or a ticket
[](https://cveledger.app/cve/CVE-2026-8959)Record last updated .