Cyber Resilience

CVE-2026-8956

Critical

Published: 19 May 2026

Published
19 May 2026
Modified
20 May 2026
KEV Added
—
Patch
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CVSS Score v3.1 9.8 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
EPSS Score 0.0060 44.6th percentile
Risk Priority 70 floored blend · peak EPSS

Summary

CVE-2026-8956 is a critical-severity Integer Overflow or Wraparound (CWE-190) vulnerability in Mozilla Firefox. Its CVSS base score is 9.8 (Critical).

Operationally, exploitation aligns with the MITRE ATT&CK technique Drive-by Compromise (T1189); ranked at the 44.6th percentile by exploit likelihood (below the median); it is not currently listed in the CISA KEV catalog.

EU & UK References

Vulnerability details

Integer overflow in the Networking: JAR component. This vulnerability was fixed in Firefox 151, Firefox ESR 140.11, Thunderbird 151, and Thunderbird 140.11.

CWE(s)
CWE-190

Related Threats

MITRE ATT&CK Enterprise TechniquesAI

T1189 Drive-by Compromise Initial Access
Adversaries may gain access to a system through a user visiting a website over the normal course of browsing.
attack.mitre.org →
T1203 Exploitation for Client Execution Execution
Adversaries may exploit software vulnerabilities in client applications to execute code.
attack.mitre.org →
Why these techniques?

Integer overflow in client-side JAR networking component directly enables remote code execution via malicious web content or crafted archives (drive-by or client exploitation).

Confidence: HIGH · MITRE ATT&CK Enterprise v19.0

CVEs Like This One

CVE-2026-2762Same product: Mozilla Firefox
CVE-2026-2774Same product: Mozilla Firefox
CVE-2026-2781Same product: Mozilla Firefox
CVE-2026-6783Same product: Mozilla Firefox
CVE-2026-0880Same product: Mozilla Firefox
CVE-2026-8949Same product: Mozilla Firefox
CVE-2025-1942Same product: Mozilla Firefox
CVE-2026-2805Same product: Mozilla Firefox
CVE-2025-1010Same product: Mozilla Firefox
CVE-2026-8962Same product: Mozilla Firefox

Affected Assets

mozilla
firefox
≤ 140.11.0 · ≤ 151.0.0
mozilla
thunderbird
≤ 140.11 · ≤ 151.0.0

Mitigating Controls

No mitigating controls mapped yet. The per-CVE control annotator has not reached this CVE.

References