CVE-2025-6427 | connect-src Content Security Policy restriction could be bypassed

An attacker was able to bypass the `connect-src` directive of a Content Security Policy by manipulating subdocuments. This would have also hidden the connections from the Network tab in Devtools. This vulnerability was fixed in Firefox 140 and Thunderbird 140.

Published: 2025-06-24 Last update: 2026-04-13 Assigner: [email protected] Source: [email protected]
NVD Status：Modified，CVE State: published
View at NVD, CVE.org, EUVD

CVE-2025-6427 is rated Moderate Risk (55.8/100): CVSS Critical severity, with medium exploitation likelihood (EPSS 0.32%). Review affected assets and schedule remediation.

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-2025-6427

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 2026-04-20 0.07% 0.32% +0.24%
2 2026-03-10 0.04% 0.07% +0.03%
3 2025-11-21 — 0.04% —

Full EPSS history (5 records total)

Common vulnerability scoring system (CVSS) metrics for CVE-2025-6427

CVSS metrics for this CVE.

Base score Version Severity Vector Exploitability Impact Score source
9.1 3.1 CRITICAL
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/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: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:N)
Service keeps running; no real outage angle.
 3.9 5.2 134c704f-9b21-4f2e-91b3-4a467353bcc0

Weakness enumeration for CVE-2025-6427

OS Trackers for CVE-2025-6427

vendor priority summary link
alpine — CVE-2025-6427: 1 source package rows (firefox); 148 state rows across 2 repos (3.22-community, edge-community); fixed 0, open 148. https://security.alpinelinux.org/vuln/CVE-2025-6427
debian not yet assigned CVE-2025-6427 not yet assigned priority: Debian including 1 source packages (firefox), 1 status rows across 1 suites (sid): resolved 1. https://security-tracker.debian.org/tracker/CVE-2025-6427
redhat medium — https://access.redhat.com/security/cve/CVE-2025-6427
suse high CVE-2025-6427 severity important: SUSE including 68 source package names (MozillaFirefox-140.0-112.270.2, MozillaFirefox-140.0.2-1.1, …), 340 product×package rows across 42 product lines (Image SLES12-SP5-SAP-Azure-LI-BYOS-Production, Image SLES12-SP5-SAP-Azure-VLI-BYOS-Production, … (42 product lines)): Fixed 340. https://www.suse.com/security/cve/CVE-2025-6427/
ubuntu medium CVE-2025-6427 medium priority: Ubuntu including 9 source packages (firefox, mozjs102, …), 58 status rows across 8 suites (bionic, focal, jammy, noble, oracular, plucky, questing, upstream): DNE 28, ignored 10, needs-triage 10, not-affected 9, released 1. https://ubuntu.com/security/CVE-2025-6427

Affected software / configurations for CVE-2025-6427

Vendor Product Version Raw CPE
mozilla firefox < 140.0 cpe:2.3:a:mozilla:firefox:*:*:*:*:-:*:*:*

References for CVE-2025-6427

cvelogic Threat Intelligence