CVE-2025-4918 | Out-of-bounds access when resolving Promise objects

Exp

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.

Published: 2025-05-17 Last update: 2026-04-13 Assigner: [email protected] Source: [email protected]
NVD Status：Modified，CVE State: published
View at NVD, CVE.org, EUVD

CVE-2025-4918 is rated High Exploit Risk (81.4/100): CVSS Critical severity, with medium exploitation likelihood (EPSS 0.99%). 2 public exploit reference(s) are indexed (Exploit-DB). Public exploits are available—assess exposure, apply mitigations, and prioritize patching.

Risk is dynamic; we continuously reassess and refresh what is shown on this page as upstream context changes.

Public exploit references (Exploit-DB) for CVE-2025-4918

EDB-ID Source Kind Published Link
— nvd_ref exploit_tag Exploit-DB ↗
— nvd_ref exploit_tag Exploit-DB ↗

Exploit prediction scoring system (EPSS) score for CVE-2025-4918

EPSS lead: Daily EPSS estimates relative likelihood of exploitation; percentile ranks this CVE among scored vulnerabilities (higher = more severe relative rank).

# Date Old EPSS score New EPSS score Delta (New - Old)
1 2026-04-24 0.76% 0.99% +0.24%
2 2026-04-22 0.61% 0.76% +0.14%
3 2026-03-13 — 0.61% —

Full EPSS history (10 records total)

Common vulnerability scoring system (CVSS) metrics for CVE-2025-4918

CVSS metrics for this CVE.

Base score Version Severity Vector Exploitability Impact Score source
9.8 3.1 CRITICAL
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H Click to expand
Attack vector (AV:N)
Could be attacked over the internet or any normal routed network—not just someone sitting at the machine.
Attack complexity (AC:L)
Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup.
Privileges required (PR:N)
No account or special rights needed—anonymous or random user is enough.
User interaction (UI:N)
Nobody has to click “OK” or open a trap file; it can work without a victim helping.
Scope (S:U)
Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:H)
Serious risk that confidential data gets exposed in a big way.
Integrity (I:H)
They could widely tamper with or forge data—trust in the data is badly hurt.
Availability (A:H)
Could take the service down hard or make it unusable for people who depend on it.
 3.9 5.9 134c704f-9b21-4f2e-91b3-4a467353bcc0

Weakness enumeration for CVE-2025-4918

OS Trackers for CVE-2025-4918

vendor priority summary link
alpine — CVE-2025-4918: 3 source package rows (firefox, firefox-esr, thunderbird); 361 state rows across 2 repos (3.22-community, edge-community); fixed 0, open 361. https://security.alpinelinux.org/vuln/CVE-2025-4918
debian not yet assigned CVE-2025-4918 not yet assigned priority: Debian including 3 source packages (firefox, firefox-esr, thunderbird), 11 status rows across 5 suites (bookworm, bullseye, forky, sid, trixie): resolved 11. https://security-tracker.debian.org/tracker/CVE-2025-4918
redhat high — https://access.redhat.com/security/cve/CVE-2025-4918
suse high CVE-2025-4918 severity important: SUSE including 34 source package names (MozillaFirefox-128.10.1-112.259.1, MozillaFirefox-128.10.1-150200.152.182.1, …), 130 product×package rows across 46 product lines (Container suse/kiosk/firefox-esr, Image SLES12-SP5-SAP-Azure-LI-BYOS-Production, … (46 product lines)): Fixed 130. https://www.suse.com/security/cve/CVE-2025-4918/
ubuntu medium CVE-2025-4918 medium priority: Ubuntu including 9 source packages (firefox, mozjs102, …), 65 status rows across 8 suites (bionic, focal, jammy, noble, oracular, plucky, questing, upstream): DNE 35, ignored 10, needs-triage 9, not-affected 9, released 2. https://ubuntu.com/security/CVE-2025-4918

Affected software / configurations for CVE-2025-4918

Vendor Product Version Raw CPE
mozilla firefox < 115.23.1 cpe:2.3:a:mozilla:firefox:*:*:*:*:esr:*:*:*
mozilla firefox < 138.0.4 cpe:2.3:a:mozilla:firefox:*:*:*:*:-:*:*:*
mozilla firefox >= 116.0, < 128.10.1 cpe:2.3:a:mozilla:firefox:*:*:*:*:esr:*:*:*
mozilla thunderbird < 128.10.2 cpe:2.3:a:mozilla:thunderbird:*:*:*:*:*:*:*:*
mozilla thunderbird >= 138.0, < 138.0.2 cpe:2.3:a:mozilla:thunderbird:*:*:*:*:-:*:*:*

References for CVE-2025-4918

URL Tags
https://bugzilla.mozilla.org/show_bug.cgi?id=1966612 Permissions Required
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://lists.debian.org/debian-lts-announce/2025/05/msg00024.html
https://lists.debian.org/debian-lts-announce/2025/05/msg00046.html
https://www.vicarius.io/vsociety/posts/cve-2025-4918-detect-firefox-out-of-bounds-write Exploit Third Party Advisory
https://www.vicarius.io/vsociety/posts/cve-2025-4918-mitigate-firefox-out-of-bounds-write Exploit Third Party Advisory
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