Is CVE-2026-8959 actively exploited?

No active exploitation of CVE-2026-8959 has been confirmed so far. Continue monitoring, as exploit status can change.

Can CVE-2026-8959 be exploited remotely?

Yes. CVE-2026-8959 is exploitable remotely over the network (CVSS attack vector: Network).

What is the CVSS score of CVE-2026-8959?

CVE-2026-8959 has a CVSS score of 9.6 (CRITICAL).

HOME VULNERABILITIESCVE-2026-8959

CRITICAL

CVE-2026-8959

Published: May 19, 2026· Updated: May 20, 2026

9.6

CVSS v3.1

EPSS:0.08%probability of exploitation in 30 daysPercentile:24.1th

Official 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.

NVD Source

Risk Analysis

This critical vulnerability allows an attacker to escape the sandbox environment in Mozilla Firefox and Thunderbird due to incorrect boundary conditions. With a CVSS score of 9.6, this flaw poses a significant risk for compromise, even though its EPSS score is currently unavailable, suggesting an unknown likelihood of exploitation. The high severity indicates that successful exploitation could lead to full system compromise.

No public exploit is currently known for this vulnerability. However, its network attack vector and low attack complexity suggest it is remotely exploitable, requiring user interaction.

Recommended Action

To mitigate this vulnerability, users should upgrade to Firefox 151, Firefox ESR 140.11, Thunderbird 151, or Thunderbird 140.11. Regularly updating browser and email client software is crucial to address such critical security flaws.

Generated by the CTIWATCH analysis pipeline from this CVE's metadata (CVSS, EPSS, KEV status, exploit intelligence). Verify against vendor advisories before acting.

Technical Analysis

CVE-2026-8959 can be exploited remotely over the network without requiring physical or adjacent access, significantly expanding the attack surface for threat actors.

Exploitation does not require any privileges, though user interaction (Required) is needed, which slightly reduces the risk of mass automated attacks.

A successful exploit results in complete confidentiality breach (data exposure), full integrity compromise (data manipulation), availability disruption (denial of service), with a CVSS base score of 9.6.

The vulnerability has a "Changed" scope, meaning successful exploitation can impact components beyond the vulnerable component itself — such as the host operating system or adjacent services.