What’s Vulnerable › Vulnerabilities

CVE-2026-6754: Use-after-free in the JavaScript Engine component

• Severity: high (CVSS 7.5 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.4% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2026-04-21 · updated 2026-10-25
• Weakness: CWE-416

Description

Use-after-free in the JavaScript Engine component. This vulnerability was fixed in Firefox 150, Firefox ESR 115.35, Firefox ESR 140.10, Thunderbird 150, and Thunderbird 140.10.

Affected products

• Mozilla Firefox: before 115.35.0; before 150.0; from 140.0 before 140.10.0 — fixed in 115.35.0, 150.0, 140.10.0
• Mozilla Thunderbird: before 140.10.0 — fixed in 140.10.0

How to fix

Upgrade to a fixed version: Mozilla Firefox 115.35.0, 150.0, 140.10.0; Mozilla Thunderbird 140.10.0. Check the vendor advisory for mitigations.

References

• https://bugzilla.mozilla.org/show_bug.cgi?id=2027541
• https://www.mozilla.org/security/advisories/mfsa2026-30/
• https://www.mozilla.org/security/advisories/mfsa2026-31/
• https://www.mozilla.org/security/advisories/mfsa2026-32/
• https://www.mozilla.org/security/advisories/mfsa2026-33/
• https://www.mozilla.org/security/advisories/mfsa2026-34/
• https://access.redhat.com/errata/RHSA-2026:10757
• https://access.redhat.com/errata/RHSA-2026:10766
• https://access.redhat.com/errata/RHSA-2026:10767
• https://access.redhat.com/errata/RHSA-2026:12285
• https://access.redhat.com/errata/RHSA-2026:13537
• https://access.redhat.com/errata/RHSA-2026:15892

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