CVE-2025-6434Public exploitNetwork attack vector

HTTP downgrade via clickjacked HTTPS-Only exception

Published Jun 24, 2025 · Updated Apr 13, 2026

Clickjacking in Mozilla Firefox and Thunderbird before 140 allows remote attackers to load a webpage over HTTP through user interaction. The HTTPS-Only exception page kept its Continue button actionable after losing focus, so a popup could cover the page until its timer expired and then close over a click. The victim must enable HTTPS-Only mode, visit an HTTP site, and double-click attacker-controlled content; the resulting exception permits insecure HTTP loading.

CVSS severity4.3
Medium
EPSS probability0.26%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Clickjacking in Mozilla Firefox and Thunderbird before 140 allows remote attackers to load a webpage over HTTP through user interaction. The HTTPS-Only exception page kept its Continue button actionable after losing focus, so a popup could cover the page until its timer expired and then close over a click. The victim must enable HTTPS-Only mode, visit an HTTP site, and double-click attacker-controlled content; the resulting exception permits insecure HTTP loading.

The record

CVE
CVE-2025-6434
Published
Jun 24, 2025
Updated
Apr 13, 2026
Vendor
Unknown vendor
Product
Unknown product
Classifications
CWE-1021, T1204.001
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

5.4SUSECVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:L/A:N
5.1SUSECVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:A/VC:L/VI:L/VA:N/SC:N/SI:N/SA:N
4.3CISA-ADPCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:L/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.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

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-1021Improper Restriction of Rendered UI Layers or Frames
T1204.001User Execution: Malicious Link

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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