CVE-2025-4083Network attack vector

Process isolation bypass via incorrect remote-type fallback

Published Apr 29, 2025 · Updated Jul 25, 2026

Process isolation bypass in Mozilla Firefox and Thunderbird before 138 allows remote attackers to run iframe content in the wrong process. When a cross-origin iframe opens a javascript: link in a new tab or window, frontend code falls back to the top-level document's remote type instead of the triggering frame's remote type. Reachability requires a user to command-click or control-click the crafted link; affected ESR branches are before 115.23 and 128.10.

CVSS severity9.1
Critical
EPSS probability0.43%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
Coverage for this vulnerability

See if you're affected

Explore vulnerability checks for your environment with Hinoki.

Book a demo

Summary

What happened

Process isolation bypass in Mozilla Firefox and Thunderbird before 138 allows remote attackers to run iframe content in the wrong process. When a cross-origin iframe opens a javascript: link in a new tab or window, frontend code falls back to the top-level document's remote type instead of the triggering frame's remote type. Reachability requires a user to command-click or control-click the crafted link; affected ESR branches are before 115.23 and 128.10.

The record

CVE
CVE-2025-4083
Published
Apr 29, 2025
Updated
Jul 25, 2026
Vendor
Unknown vendor
Product
Unknown product
Classifications
CWE-653, T1203
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Apr 29, 2025CVE publishedPublication date reported by the CVE source.
  2. Jul 25, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

Compare your product and version with the public record. A matching version still requires validation against your environment.

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.

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 exploitUnconfirmed

Weakness, pattern, technique

CWE-653Improper Isolation or Compartmentalization
T1203Exploitation for Client Execution

Public exploit references

No public exploit references are available in this record.

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

Technologies

Your stack

See the directory against your own environment.

Your stack

Check the software in your environment

Book a demo to see how Hinoki identifies affected software and validates exploitability in your environment.

Book a demo