CVE-2026-8958

HIGH

Published May 19, 2026 Modified May 20, 2026 CWE-668 CWE-693

Description

Information disclosure, sandbox escape in the Security: Process Sandboxing component. This vulnerability was fixed in Firefox 151, Firefox ESR 140.11, Thunderbird 151, and Thunderbird 140.11.

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CVSS v3.1 Score

8.6

HIGH

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

EPSS — Exploit Prediction

0.0034

Probability of exploitation

0.26%

Percentile rank

EPSS estimates the probability that this vulnerability will be exploited in the wild within the next 30 days. A higher score means more likely to be exploited.

Weakness Type (CWE)

CWE-668 CWE-668

CWE-693 CWE-693

Affected Products

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

References

Advisories & Patches

https://www.mozilla.org/security/advisories/mfsa2026-46/ https://www.mozilla.org/security/advisories/mfsa2026-48/ https://www.mozilla.org/security/advisories/mfsa2026-50/ https://www.mozilla.org/security/advisories/mfsa2026-51/

Other References

https://bugzilla.mozilla.org/show_bug.cgi?id=2034713

Frequently Asked Questions

What is CVE-2026-8958? +

Information disclosure, sandbox escape in the Security: Process Sandboxing component. This vulnerability was fixed in Firefox 151, Firefox ESR 140.11, Thunderbird 151, and Thunderbird 140.11. It has a CVSS v3.1 base score of 8.6 (HIGH).

How severe is CVE-2026-8958? +

CVE-2026-8958 has a CVSS v3.1 score of 8.6 out of 10, rated HIGH. This is a high-severity vulnerability that should be prioritized for patching. The EPSS score is 0.0034, placing it in the 0th percentile for exploitation probability.

What products are affected by CVE-2026-8958? +

CVE-2026-8958 affects products from mozilla, specifically: firefox, thunderbird. Check the affected products table above for specific version ranges.

How do I check if I'm vulnerable to CVE-2026-8958? +

You can use Secably's free Website Scanner to check your website for known vulnerabilities. For infrastructure scanning, use the Port Scanner to identify exposed services that may be affected. Check the vendor advisories linked above for specific patch and version information.