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Firefox CVE-2025-6429

| EUVDEUVD-2025-21378 MEDIUM
Improper Encoding or Escaping of Output (CWE-116)
2025-06-24 security@mozilla.org
Authentication Bypass Mozilla
6.5
CVSS 3.1 · NVD
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Severity by source

NVD PRIMARY
6.5 MEDIUM
AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:H/A:N
vuln.today AI
6.5 MEDIUM

Network attack vector, low complexity, no privileges, user interaction required, integrity impact only.

3.1 AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:H/A:N
4.0 AV:N/AC:L/AT:N/PR:N/UI:P/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N
Ubuntu
MEDIUM
qualitative
SUSE
MEDIUM
qualitative
Red Hat
6.1 MEDIUM
qualitative

Primary rating from NVD.

CVSS VectorNVD

Attack Vector
Network
Attack Complexity
Low
Privileges Required
None
User Interaction
Required
Scope
Unchanged
Confidentiality
None
Integrity
High
Availability
None

Lifecycle Timeline

4
Patch released
Mar 31, 2026 - 21:13 nvd
Patch available
EUVD ID Assigned
Mar 15, 2026 - 22:36 euvd
EUVD-2025-21378
Analysis Generated
Mar 15, 2026 - 22:36 vuln.today
CVE Published
Jun 24, 2025 - 13:15 nvd
MEDIUM 6.5

DescriptionCVE.org

Firefox could have incorrectly parsed a URL and rewritten it to the youtube.com domain when parsing the URL specified in an embed tag. This could have bypassed website security checks that restricted which domains users were allowed to embed. This vulnerability affects Firefox < 140, Firefox ESR < 128.12, Thunderbird < 140, and Thunderbird < 128.12.

AnalysisAI

URL parsing bypass in Firefox and Thunderbird allows attackers to rewrite URLs to youtube.com via an embed tag, potentially bypassing website security checks that restrict embed domains. Affects Firefox < 140, Firefox ESR < 128.12, Thunderbird < 140, and Thunderbird < 128.12. No public exploit identified at time of analysis.

Technical ContextAI

The vulnerability lies in Firefox's URL parser when handling embed tags. The CWE-116 (Improper Encoding or Escaping of Output) indicates a failure to properly sanitize or validate URL components, allowing an attacker to craft a URL that is incorrectly rewritten to the youtube.com domain. This bypasses same-origin or domain whitelist checks implemented by websites. The affected products are Mozilla Firefox and Thunderbird, as identified by CPE strings cpe:2.3:a:mozilla:firefox:*:*:*:*:esr:*:*:* and cpe:2.3:a:mozilla:firefox:*:*:*:*:-:*:*:*.

RemediationAI

Update to Firefox 140 or later, Firefox ESR 128.12 or later, Thunderbird 140 or later, or Thunderbird ESR 128.12 or later. Patches are available from Mozilla. For Linux distributions, apply updates via USN-7663-1 (Ubuntu) or DSA-5950-1 (Debian). No workarounds are documented; upgrading is the recommended action.

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Same weakness CWE-116 – Improper Encoding or Escaping of Output

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Vendor StatusVendor

Ubuntu

Priority: Medium
mozjs52
Release Status Version
focal ignored -
jammy DNE -
noble DNE -
bionic ignored -
oracular DNE -
plucky DNE -
upstream needs-triage -
questing DNE -
firefox
Release Status Version
jammy not-affected code not present
noble not-affected code not present
oracular not-affected code not present
plucky not-affected code not present
upstream needs-triage -
questing not-affected code not present
thunderbird
Release Status Version
noble not-affected code not present
oracular not-affected code not present
plucky not-affected code not present
jammy released 1:128.12.0+build1-0ubuntu0.22.04.1
upstream released 128.12
questing not-affected code not present
mozjs38
Release Status Version
bionic needs-triage -
jammy DNE -
noble DNE -
oracular DNE -
plucky DNE -
upstream needs-triage -
questing DNE -
mozjs68
Release Status Version
focal ignored -
jammy DNE -
noble DNE -
oracular DNE -
plucky DNE -
upstream needs-triage -
questing DNE -
mozjs78
Release Status Version
jammy ignored -
noble DNE -
oracular DNE -
plucky DNE -
upstream needs-triage -
questing DNE -
mozjs91
Release Status Version
jammy ignored -
noble DNE -
oracular DNE -
plucky DNE -
upstream needs-triage -
questing DNE -
mozjs102
Release Status Version
jammy ignored -
noble ignored -
oracular DNE -
plucky DNE -
upstream needs-triage -
questing DNE -
mozjs115
Release Status Version
jammy DNE -
noble ignored -
oracular ignored -
plucky ignored -
upstream needs-triage -
questing DNE -
USN-7663-1

Debian

firefox
Release Status Fixed Version Urgency
sid fixed 148.0.2-1 -
(unstable) fixed 140.0-1 -
firefox-esr
Release Status Fixed Version Urgency
bullseye fixed 128.12.0esr-1~deb11u1 -
bullseye (security) fixed 140.8.0esr-1~deb11u1 -
bookworm fixed 128.12.0esr-1~deb12u1 -
bookworm (security) fixed 140.8.0esr-1~deb12u1 -
trixie (security), trixie fixed 140.8.0esr-1~deb13u1 -
forky, sid fixed 140.8.0esr-1 -
(unstable) fixed 128.12.0esr-1 -
thunderbird
Release Status Fixed Version Urgency
bullseye fixed 1:128.12.0esr-1~deb11u1 -
bullseye (security) fixed 1:140.8.0esr-1~deb11u1 -
bookworm fixed 1:128.12.0esr-1~deb12u1 -
bookworm (security) fixed 1:140.8.0esr-1~deb12u1 -
trixie (security), trixie fixed 1:140.8.0esr-1~deb13u1 -
forky, sid fixed 1:140.8.0esr-1 -
(unstable) fixed 1:128.12.0esr-1 -
DLA-4231-1 DLA-4239-1 DSA-5950-1 DSA-5959-1

SUSE

Severity: Medium
Product Status
Container suse/sl-micro/6.0/kvm-os-container:2.1.3-4.11 Affected
Image SLES12-SP5-SAP-Azure-LI-BYOS-Production Image SLES12-SP5-SAP-Azure-VLI-BYOS-Production Affected
Image SLES15-SP4-SAP-Azure-LI-BYOS Image SLES15-SP4-SAP-Azure-LI-BYOS-Production Image SLES15-SP4-SAP-Azure-VLI-BYOS Image SLES15-SP4-SAP-Azure-VLI-BYOS-Production Affected
Image SLES15-SP5-SAP-Azure-LI-BYOS Image SLES15-SP5-SAP-Azure-LI-BYOS-Production Image SLES15-SP5-SAP-Azure-VLI-BYOS Image SLES15-SP5-SAP-Azure-VLI-BYOS-Production Affected
Image SLES15-SP6-SAP-Azure-LI-BYOS Image SLES15-SP6-SAP-Azure-LI-BYOS-Production Image SLES15-SP6-SAP-Azure-VLI-BYOS Image SLES15-SP6-SAP-Azure-VLI-BYOS-Production Image SLES15-SP7-SAP-Azure-LI-BYOS-Production Image SLES15-SP7-SAP-Azure-VLI-BYOS-Production Affected

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CVE-2025-6429 vulnerability details – vuln.today
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