CVE-2025-6427Public exploitNetwork attack vector

Policy bypass via detached subdocument ClientInfo loss

Published Jun 24, 2025 · Updated Apr 13, 2026

Content Security Policy bypass in Mozilla Firefox and Thunderbird before 140 allows remote attackers to make blocked network requests. After a subdocument or popup is removed or closed, LoadInfo::GetCSP returns null because its ClientInfo is missing, so CSPService::ConsultCSP skips connect-src checks. A crafted page can retain a window reference and issue fetch, sendBeacon, EventSource, or WebSocket requests that bypass the inherited policy and remain absent from the DevTools Network tab.

CVSS severity9.1
Critical
EPSS probability0.34%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Content Security Policy bypass in Mozilla Firefox and Thunderbird before 140 allows remote attackers to make blocked network requests. After a subdocument or popup is removed or closed, LoadInfo::GetCSP returns null because its ClientInfo is missing, so CSPService::ConsultCSP skips connect-src checks. A crafted page can retain a window reference and issue fetch, sendBeacon, EventSource, or WebSocket requests that bypass the inherited policy and remain absent from the DevTools Network tab.

The record

CVE
CVE-2025-6427
Published
Jun 24, 2025
Updated
Apr 13, 2026
Vendor
Unknown vendor
Product
Unknown product
Classifications
CWE-693
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

9.1CISA-ADPCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/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 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-693Protection Mechanism Failure

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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