Remote code execution in Mozilla Firefox and Firefox ESR

Published: 2025-05-18 | Updated: 2025-05-22

Risk	High
Patch available	YES
Number of vulnerabilities	2
CVE-ID	CVE-2025-4918 CVE-2025-4920 CVE-2025-4919 CVE-2025-4921
CWE-ID	CWE-787
Exploitation vector	Network
Public exploit	N/A
Vulnerable software	Mozilla Firefox Client/Desktop applications / Web browsers Firefox ESR Client/Desktop applications / Web browsers
Vendor	Mozilla

Security Bulletin

This security bulletin contains information about 2 vulnerabilities.

1) Out-of-bounds write

EUVDB-ID: #VU109400

Risk: High

CVSSv4.0: 6.1 [CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:A/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N/E:U/U:Amber]

CVE-ID: CVE-2025-4918,CVE-2025-4920

CWE-ID: CWE-787 - Out-of-bounds write

Exploit availability: No

Description

The vulnerability allows a remote attacker to compromise vulnerable system.

The vulnerability exists due to a boundary error when processing JavaScript "Promise" object. A remote attacker can trick the victim into visiting a specially crafted website, trigger an out-of-bounds write and execute arbitrary code on the target system.

Mitigation

Install updates from vendor's website.

Vulnerable software versions

Mozilla Firefox: 110.0 - 138.0.3

Firefox ESR: 102.0 - 128.10.0

CPE2.3

External links

https://bugzilla.mozilla.org/show_bug.cgi?id=1966612
https://www.mozilla.org/security/advisories/mfsa2025-36/
https://www.mozilla.org/security/advisories/mfsa2025-37/
https://www.mozilla.org/en-US/security/advisories/mfsa2025-38/

Q & A

Can this vulnerability be exploited remotely?

Yes. This vulnerability can be exploited by a remote non-authenticated attacker via the Internet.

How the attacker can exploit this vulnerability?

The attacker would have to trick the victim to visit a specially crafted website.

Is there known malware, which exploits this vulnerability?

No. We are not aware of malware exploiting this vulnerability.

2) Out-of-bounds write

EUVDB-ID: #VU109401