CVE-2025-5263Public exploitNetwork attack vector

Cross-origin data disclosure via side-effectful error conversion

Published May 27, 2025 · Updated Apr 13, 2026

Origin validation error in Mozilla Firefox and Thunderbird allows remote attackers to read cross-origin content through script errors. ScriptLoader error reporting converts a muted cross-origin exception with side effects enabled, invoking attacker-modified Error properties that expose the error message. Exploitation requires a victim to load an attacker-controlled page and a targeted response whose UTF-16 decoding forms a valid JavaScript identifier.

CVSS severity4.3
Medium
EPSS probability0.25%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Origin validation error in Mozilla Firefox and Thunderbird allows remote attackers to read cross-origin content through script errors. ScriptLoader error reporting converts a muted cross-origin exception with side effects enabled, invoking attacker-modified Error properties that expose the error message. Exploitation requires a victim to load an attacker-controlled page and a targeted response whose UTF-16 decoding forms a valid JavaScript identifier.

The record

CVE
CVE-2025-5263
Published
May 27, 2025
Updated
Apr 13, 2026
Vendor
Unknown vendor
Product
Unknown product
Classifications
CWE-346
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

4.3UbuntuCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:N/A:N
4.3SUSECVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:N/A:N
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.

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

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-346Origin Validation Error

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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