CVE-2025-4918: Mozilla Firefox buffer overflow (CVSS 9.8)

Description

An attacker was able to perform an out-of-bounds read or write on a JavaScript `Promise` object. This vulnerability was fixed in Firefox 138.0.4, Firefox ESR 128.10.1, Firefox ESR 115.23.1, Thunderbird 128.10.2, and Thunderbird 138.0.2.

CVSS 3.1 breakdown

Attack vectorNetwork

Attack complexityLow

Privileges requiredNone

User interactionNone

ScopeUnchanged

ConfidentialityHigh

IntegrityHigh

AvailabilityHigh

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

Affected products

Mozilla Firefox< 138.0.4 · ≥ 116.0 < 128.10.1 · < 115.23.1

Mozilla Thunderbird< 128.10.2 · ≥ 138.0 < 138.0.2

Remediation

Fixed in

Mozilla Firefox≥ 138.0.4

Mozilla Thunderbird≥ 128.10.2

Patch & vendor advisories

References

https://bugzilla.mozilla.org/show_bug.cgi?id=1966612Permissions Required
https://lists.debian.org/debian-lts-announce/2025/05/msg00024.html
https://lists.debian.org/debian-lts-announce/2025/05/msg00046.html
https://www.mozilla.org/security/advisories/mfsa2025-36/Vendor Advisory
https://www.mozilla.org/security/advisories/mfsa2025-37/Vendor Advisory
https://www.mozilla.org/security/advisories/mfsa2025-38/Vendor Advisory
https://www.mozilla.org/security/advisories/mfsa2025-40/Vendor Advisory
https://www.mozilla.org/security/advisories/mfsa2025-41/Vendor Advisory
https://www.vicarius.io/vsociety/posts/cve-2025-4918-detect-firefox-out-of-bounds-writeExploitThird Party Advisory
https://www.vicarius.io/vsociety/posts/cve-2025-4918-mitigate-firefox-out-of-bounds-writeExploitThird Party Advisory

Related CVEs

Recent high-severity vulnerabilities sharing a weakness type.

Frequently asked

Is CVE-2025-4918 being actively exploited?

CVE-2025-4918 is not in the CISA KEV catalog. A public exploit reference exists, so treat it as exploitable. Its EPSS exploit probability is 9.38%.

How severe is CVE-2025-4918?

CVE-2025-4918 has a CVSS 3.1 base score of 9.8, rated critical. EPSS estimates a 9.38% probability of exploitation.

Which products are affected by CVE-2025-4918?

Affected products include Mozilla Firefox, Mozilla Thunderbird.

How do I fix CVE-2025-4918?

Upgrade affected software to a fixed version, for example Mozilla Firefox 138.0.4, Mozilla Thunderbird 128.10.2 or later, then confirm no affected versions remain in your inventory.

How Secuno handles this

Secuno correlates vulnerabilities like CVE-2025-4918 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.

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