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.
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Score 9.6 from GitHub Security Advisory (severity: CRITICAL) published 2026-05-19. NVD baseline CVSS 9.6; sources differ by 0.0.
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.
May 19, 2026
May 20, 2026
These vendors published their own advisory mentioning this CVE — often with vendor-specific remediation steps + affected product lists not in NVD.
Red Hat Security Advisory: thunderbird security update
Red Hat Security Advisory: thunderbird security update
Sandbox escape due to incorrect boundary conditions in the Widget: Win32 component. This...
| Vendor / Ecosystem | Fixed in / Patch | Released | Source |
|---|---|---|---|
| redhat | thunderbird-0:140.11.0-1.el8_10 | 2026-06-03 | redhat |
| redhat | thunderbird-0:140.11.0-1.el10_2 | 2026-06-01 | redhat |
| redhat | thunderbird-0:140.11.0-1.el9_8 | 2026-05-27 | redhat |
Patches are aggregated from vendor advisories (Red Hat, Microsoft, Cisco, GitHub) and package ecosystems (OSV, GHSA). Multiple rows for the same upstream release have been deduplicated.
MITRE Common Weakness Enumeration — the root-cause categories this CVE belongs to.
Vendors that published advisories for this CVE beyond the curated set above. Broader coverage but minimal per-row detail — click through for the original advisory.
Every time one of our enrichment pipelines (NVD, MITRE cvelistV5, EPSS, CISA KEV, GHSA, OSV, vendor advisories) ran against this CVE. Most recent first.
See which npm, PyPI, Go, and Maven packages are affected by CVE-2026-8959
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redhat
CWE-20 · CWE-119