SB2025051812 - Remote code execution in Mozilla Firefox and Firefox ESR

Description

This security bulletin contains information about 2 secuirty vulnerabilities.

1) Out-of-bounds write (CVE-ID: CVE-2025-4920)

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.

2) Out-of-bounds write (CVE-ID: CVE-2025-4921)

The vulnerability allows a remote attacker to compromise vulnerable system.

The vulnerability exists due to a boundary error when manipulating a JavaScript object by confusing array index sizes. 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.

Remediation

Install update from vendor's website.

References

• 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/
• https://bugzilla.mozilla.org/show_bug.cgi?id=1966614
• https://www.zerodayinitiative.com/advisories/ZDI-25-292/
• https://www.zerodayinitiative.com/advisories/ZDI-25-291/