CVE-2025-6429Public exploitNetwork attack vector

Embedded-content filter bypass via non-strict URL rewriting

Published Jun 24, 2025 · Updated Apr 13, 2026

URL validation bypass in Firefox and Thunderbird before 140 or ESR before 128.12 allows remote attackers to load an unexpected host via embed tags. nsObjectLoadingContent::MaybeRewriteYoutubeEmbed replaces the first ampersand across the entire URL specification instead of limiting replacement to its path, query, and fragment, causing crafted user information to change the loaded host. Exploitation requires user interaction with content that embeds an attacker-controlled URL after accepting its original YouTube host, and the resulting subframe loads unexpected remote content.

CVSS severity6.5
Medium
EPSS probability0.33%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

URL validation bypass in Firefox and Thunderbird before 140 or ESR before 128.12 allows remote attackers to load an unexpected host via embed tags. nsObjectLoadingContent::MaybeRewriteYoutubeEmbed replaces the first ampersand across the entire URL specification instead of limiting replacement to its path, query, and fragment, causing crafted user information to change the loaded host. Exploitation requires user interaction with content that embeds an attacker-controlled URL after accepting its original YouTube host, and the resulting subframe loads unexpected remote content.

The record

CVE
CVE-2025-6429
Published
Jun 24, 2025
Updated
Apr 13, 2026
Vendor
Unknown vendor
Product
Unknown product
Classifications
CWE-116
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jun 24, 2025CVE publishedPublication date reported by the CVE source.
  2. Apr 13, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Affected buildAffected product and version details are unavailable.

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Affected products and versions are unavailable in this record.

Published CVSS scores

6.5CISA-ADPCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:H/A:N

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

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No observations available

Sep 9, 2026Sep 15, 2026
Latest reporting daySep 15, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-116Improper Encoding or Escaping of Output

Public exploit references

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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