CVE-2025-6427
published 2025-06-24CVE-2025-6427: An attacker was able to bypass the `connect-src` directive of a Content Security Policy by manipulating subdocuments. This would have also hidden the…
PriorityP349critical9.1CVSS 3.1
AVNACLPRNUINSUCHIHAN
EPSS
0.37%
29.5th percentile
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.
Affected
4 ranges
| Vendor | Product | Version range | Fixed in |
|---|---|---|---|
| debian | firefox | < firefox 140.0-1 (sid) | firefox 140.0-1 (sid) |
| mozilla | firefox | < 140.0 | 140.0 |
| mozilla | firefox | — | — |
| mozilla | thunderbird | >= 0 < 1:140.7.1+build1-0ubuntu0.22.04.1 | 1:140.7.1+build1-0ubuntu0.22.04.1 |
CVSS provenance
nvdv3.19.1CRITICALCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N
osv9.1CRITICAL
vendor_debian9.1CRITICAL
vendor_redhat9.1CRITICAL
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Ubuntu
Thunderbird vulnerabilities
vendor_ubuntu·2026-02-02
CVE-2025-8031 Thunderbird vulnerabilities
Title: Thunderbird vulnerabilities
Summary: Several security issues were fixed in Thunderbird.
Multiple security issues were discovered in Thunderbird. If a user were
tricked into opening a specially crafted website in a browsing context,
an attacker could potentially exploit these to cause a denial of service,
obtain sensitive information, bypass security restrictions, cross-site
tracing, or execute arbitrary code.
Instructions: In general, a standard system update will make all the necessary changes.
Red Hat
firefox: connect-src Content Security Policy restriction could be bypassed
vendor_redhat·2025-06-24·CVSS 9.1
CVE-2025-6427 [CRITICAL] firefox: connect-src Content Security Policy restriction could be bypassed
firefox: 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 affects Firefox connect-src directive of a Content Security Policy by manipulating subdocuments. This also hides the connections from the Network tab in Devtools.
Statement: Red Hat Product Security rates the severity of this flaw as determined by the Mozilla Foundation Security Advisory.
Package: firefox (Red Hat Enterprise Linux 10) - Not affected
Package: rhel10/firefox-flatpak (Red Hat Enterprise Linux 10) - Not affected
Package: firefox (Red Hat Enterprise Linux 6) - Not affected
Package: firef
Debian
CVE-2025-6427: firefox - An attacker was able to bypass the `connect-src` directive of a Content Security...
vendor_debian·2025·CVSS 9.1
CVE-2025-6427 [CRITICAL] CVE-2025-6427: firefox - An attacker was able to bypass the `connect-src` directive of a Content Security...
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 affects Firefox < 140 and Thunderbird < 140.
Scope: local
sid: resolved (fixed in 140.0-1)
Mozilla
Mozilla Foundation Security Advisory 2025-51: CVE-2025-6427
vendor_mozilla·CVSS 9.1
CVE-2025-6427 [CRITICAL] Mozilla Foundation Security Advisory 2025-51: CVE-2025-6427
Mozilla Foundation Security Advisory 2025-51
CVE: CVE-2025-6427
Product: Firefox
Impact: high
Fixed in: Firefox 140
Mozilla
Mozilla Foundation Security Advisory 2025-54: CVE-2025-6427
vendor_mozilla·CVSS 9.1
CVE-2025-6427 [CRITICAL] Mozilla Foundation Security Advisory 2025-54: CVE-2025-6427
Mozilla Foundation Security Advisory 2025-54
CVE: CVE-2025-6427
Product: Thunderbird
Impact: high
Fixed in: Thunderbird 140
GHSA
GHSA-823q-pcrj-c4xv: An attacker was able to bypass the `connect-src` directive of a Content Security Policy by manipulating subdocuments
ghsa_unreviewed·2025-06-26
CVE-2025-6427 [CRITICAL] CWE-693 GHSA-823q-pcrj-c4xv: An attacker was able to bypass the `connect-src` directive of a Content Security Policy by manipulating subdocuments
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 affects Firefox < 140.
OSV
CVE-2025-6427: An attacker was able to bypass the `connect-src` directive of a Content Security Policy by manipulating subdocuments
osv·2025-06-24·CVSS 9.1
CVE-2025-6427 [CRITICAL] CVE-2025-6427: An attacker was able to bypass the `connect-src` directive of a Content Security Policy by manipulating subdocuments
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 affects Firefox < 140 and Thunderbird < 140.
No detection rules found.
No public exploits indexed.
Bugzilla
Detached iframe WebTransport loses ClientInfo and bypasses connect-src CSP
bugzilla·2026-05-23·CVSS 9.1
CVE-2025-6427 [CRITICAL] Detached iframe WebTransport loses ClientInfo and bypasses connect-src CSP
Detached iframe WebTransport loses ClientInfo and bypasses connect-src CSP
Created attachment 9589139
poc.html
Summary:
Bug 1966927 (CVE-2025-6427) fixed a class of CSP bypasses in which a discarded or detached subdocument could start new network requests without the original document's ClientInfo / policy container. In current Firefox builds, the original fetch/XHR/sendBeacon/EventSource/WebSocket-style paths are blocked, but the WebTransport path still allows a detached iframe global to initiate a connection attempt that should be blocked by `connect-src`.
Steps to Reproduce:
The attached PoC uses the following CSP rule:
```html
```
1. Open `poc.html`.
2. Observe the DevTools Network tab and DevTools Console output.
The PoC uses two public W3C WebTransport echo endpoints so tha
Bugzilla
CVE-2025-6427 firefox: connect-src Content Security Policy restriction could be bypassed
bugzilla·2025-06-24·CVSS 9.1
CVE-2025-6427 [CRITICAL] CVE-2025-6427 firefox: connect-src Content Security Policy restriction could be bypassed
CVE-2025-6427 firefox: 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 affects Firefox < 140.
2025-06-24
Published