CVE-2025-5266 | Script element events leaked cross-origin resource status

Script elements loading cross-origin resources generated load and error events which leaked information enabling XS-Leaks attacks. This vulnerability was fixed in Firefox 139, Firefox ESR 128.11, Thunderbird 139, and Thunderbird 128.11.

Published: 2025-05-27 Last update: 2026-04-13 Assigner: [email protected] Source: [email protected]
NVD Status：Modified，CVE State: published
View at NVD, CVE.org, EUVD

CVE-2025-5266 is rated Low Risk (39.5/100): CVSS Medium severity, with medium exploitation likelihood (EPSS 0.43%). Monitor for updates and reassess as exploit intelligence or EPSS changes.

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

Exploit prediction scoring system (EPSS) score for CVE-2025-5266

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 2026-03-23 0.06% 0.43% +0.38%
2 2025-11-04 0.04% 0.06% +0.02%
3 2025-10-23 — 0.04% —

Full EPSS history (5 records total)

Common vulnerability scoring system (CVSS) metrics for CVE-2025-5266

CVSS metrics for this CVE.

Base score Version Severity Vector Exploitability Impact Score source
4.3 3.1 MEDIUM
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:N/A:N 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:R)
A real person has to do something—click, install, enable—otherwise it doesn’t land.
Scope (S:U)
Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:L)
Some sensitive info could get out, but not a total data dump.
Integrity (I:N)
Data isn’t meaningfully altered or forged.
Availability (A:N)
Service keeps running; no real outage angle.
 2.8 1.4 134c704f-9b21-4f2e-91b3-4a467353bcc0

Weakness enumeration for CVE-2025-5266

OS Trackers for CVE-2025-5266

vendor priority summary link
alpine — CVE-2025-5266: 3 source package rows (firefox, firefox-esr, thunderbird); 364 state rows across 2 repos (3.22-community, edge-community); fixed 0, open 364. https://security.alpinelinux.org/vuln/CVE-2025-5266
debian not yet assigned CVE-2025-5266 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-2025-5266
redhat medium — https://access.redhat.com/security/cve/CVE-2025-5266
suse high CVE-2025-5266 severity important: SUSE including 41 source package names (2.1.3-4.11:qemu-guest-agent-8.2.7-1.1, MozillaFirefox-128.11.0-112.262.1, …), 150 product×package rows across 50 product lines (Container suse/kiosk/firefox-esr, Container suse/sl-micro/6.0/kvm-os-container, … (50 product lines)): Fixed 147, First Fixed 3. https://www.suse.com/security/cve/CVE-2025-5266/
ubuntu medium CVE-2025-5266 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-2025-5266

Affected software / configurations for CVE-2025-5266

Vendor Product Version Raw CPE
mozilla firefox < 128.11.0 cpe:2.3:a:mozilla:firefox:*:*:*:*:esr:*:*:*
mozilla firefox < 139.0 cpe:2.3:a:mozilla:firefox:*:*:*:*:-:*:*:*

References for CVE-2025-5266

cvelogic Threat Intelligence