CVE-2025-5266Public exploitNetwork attack vector

Cross-origin status disclosure via script event differences

Published May 27, 2025 · Updated Apr 13, 2026

Information disclosure in Mozilla Firefox and Thunderbird before 139, including ESR before 128.11, allows remote attackers to infer resource status. The DOM script loader emitted different load and error events for cross-origin resources based on request success, exposing a cross-origin status oracle. Exploitation requires attacker-controlled web content to be loaded; Thunderbird disables scripting while reading mail, but browser-like contexts can reveal login state or resource existence.

CVSS severity4.3
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

Information disclosure in Mozilla Firefox and Thunderbird before 139, including ESR before 128.11, allows remote attackers to infer resource status. The DOM script loader emitted different load and error events for cross-origin resources based on request success, exposing a cross-origin status oracle. Exploitation requires attacker-controlled web content to be loaded; Thunderbird disables scripting while reading mail, but browser-like contexts can reveal login state or resource existence.

The record

CVE
CVE-2025-5266
Published
May 27, 2025
Updated
Apr 13, 2026
Vendor
Unknown vendor
Product
Unknown product
Classifications
CWE-200
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. May 27, 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

4.3CISA-ADPCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:N/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-200Exposure of Sensitive Information to an Unauthorized Actor

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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