CVE-2025-4083: Mozilla Firefox vulnerability (CVSS 9.1)

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.

CVSS 3.1 breakdown

Attack vectorNetwork

Attack complexityLow

Privileges requiredNone

User interactionNone

ScopeUnchanged

ConfidentialityHigh

IntegrityHigh

AvailabilityNone

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

Affected products

Mozilla Firefox< 138.0 · ≥ 128.0 < 128.10 · < 115.23

Mozilla Thunderbird< 138.0 · < 128.10.0

Remediation

Fixed in

Mozilla Firefox≥ 138.0

Mozilla Thunderbird≥ 138.0

Patch & vendor advisories

References

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

Related CVEs

Recent high-severity vulnerabilities sharing a weakness type.

Frequently asked

Is CVE-2025-4083 being actively exploited?

CVE-2025-4083 is not in the CISA KEV catalog. Its EPSS exploit probability is 0.45%.

How severe is CVE-2025-4083?

CVE-2025-4083 has a CVSS 3.1 base score of 9.1, rated critical. EPSS estimates a 0.45% probability of exploitation.

Which products are affected by CVE-2025-4083?

Affected products include Mozilla Firefox, Mozilla Thunderbird.

How do I fix CVE-2025-4083?

Upgrade affected software to a fixed version, for example Mozilla Firefox 138.0, Mozilla Thunderbird 138.0 or later, then confirm no affected versions remain in your inventory.

How Secuno handles this

Secuno correlates vulnerabilities like CVE-2025-4083 against the real software inventory on every managed device, every day. Rather than a static severity, each match is scored in context: exploit availability, EPSS, the asset's exposure, and business criticality decide where it lands in the queue. If an affected version is present anywhere across your portfolio, it surfaces automatically with a prioritised remediation path.

See how prioritisation works Book a demo