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CVE-2025-4083: Process isolation bypass using "javascript:" URI links in cross-origin frames

• Severity: critical (CVSS 9.1 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.5% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2025-04-29 · updated 2026-10-05
• Weakness: CWE-653

Description

A process isolation vulnerability in Thunderbird stemmed from improper handling of javascript: URIs, which could allow content to execute in the top-level document's process instead of the intended frame, potentially enabling a sandbox escape. This vulnerability was fixed in Firefox 138, Firefox ESR 128.10, Firefox ESR 115.23, Thunderbird 138, and Thunderbird 128.10.

Affected products

• Mozilla Firefox: before 115.23; before 138.0; from 128.0 before 128.10 — fixed in 115.23, 128.10, 138.0
• Mozilla Thunderbird: before 128.10.0; before 138.0 — fixed in 128.10.0, 138.0

How to fix

Upgrade to a fixed version: Mozilla Firefox 115.23, 128.10, 138.0; Mozilla Thunderbird 128.10.0, 138.0. Check the vendor advisory for mitigations.

References

• https://bugzilla.mozilla.org/show_bug.cgi?id=1958350
• https://www.mozilla.org/security/advisories/mfsa2025-28/
• https://www.mozilla.org/security/advisories/mfsa2025-29/
• https://www.mozilla.org/security/advisories/mfsa2025-30/
• https://www.mozilla.org/security/advisories/mfsa2025-31/
• https://www.mozilla.org/security/advisories/mfsa2025-32/
• https://lists.debian.org/debian-lts-announce/2025/05/msg00024.html

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