CVE-2026-8959

⛔ critical

Summary

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.

CVSS Score

9.6

Critical

EPSS Score

0.2

Exploit Probability

Published Date

2026-05-19

First Seen: 2026-05-20

📊 Relative Risk Intelligence

This CVE is Very High Risk - more severe than 90.2% of all 328,009 vulnerabilities in our database.

#32,050

Top 10% most severe

Severity Percentile

🎯 CISA SSVC Assessment Updated: May 19, 2026

🔍 Exploitation Status

None

No known exploits

⚙️ Automatable

Requires human interaction

💥 Technical Impact

Total

Complete system compromise possible

🏆 Discovered By

Ameen Basha M K

SSVC data provided by CISA

Last Modified 2026-05-20

Source NVD 🔗

CVSS Vector 3.1 CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:H/A:H

CWE IDs (Weakness Types)

CWE-20 CWE-119 CWE-693

📦 Affected Products 4

Vendor	Product	Status	Affected Versions
mozilla	firefox	Affected	< 140.11.0
mozilla	firefox	Affected	< 151.0.0
mozilla	thunderbird	Affected	< 140.11
mozilla	thunderbird	Affected	< 151.0.0

🔗 References 5

https://bugzilla.mozilla.org/show_bug.cgi?id=2034754

Permissions Required

https://www.mozilla.org/security/advisories/mfsa2026...

Vendor Advisory

https://www.mozilla.org/security/advisories/mfsa2026...

Vendor Advisory

https://www.mozilla.org/security/advisories/mfsa2026...

Vendor Advisory

https://www.mozilla.org/security/advisories/mfsa2026...

Vendor Advisory

🔗 Related CVEs 6

CVE ID	Severity	CVSS	EPSS	Summary	Published
CVE-2026-12289	⚠️ high	8.8	-	Privilege escalation in the Graphics: WebRender component. This vulnerability was fixed in Firefox 152, Firefox ESR 140....	2026-06-16
CVE-2026-12298	🔶 medium	5.4	-	Memory safety bug fixed in Thunderbird 152. This vulnerability was fixed in Firefox 152, Firefox ESR 140.12, Thunderbird...	2026-06-16
CVE-2026-12299	🔶 medium	5.4	-	JIT miscompilation in the DOM: Core & HTML component. This vulnerability was fixed in Firefox 152, Firefox ESR 140.12, F...	2026-06-16
CVE-2026-12303	🔶 medium	4.3	-	Information disclosure due to incorrect boundary conditions in the Graphics: WebGPU component. This vulnerability was fi...	2026-06-16
CVE-2026-12311	🔶 medium	4.7	-	Information disclosure, sandbox escape in the Security: Process Sandboxing component. This vulnerability was fixed in Fi...	2026-06-16
CVE-2026-12313	🔶 medium	4.7	-	Information disclosure, sandbox escape in the Security: Process Sandboxing component. This vulnerability was fixed in Fi...	2026-06-16

These CVEs affect the same products