CVE-2025-3522Network attack vector

Windows credential-hash disclosure via unsanitized attachment URL

Published Apr 15, 2025 · Updated Apr 13, 2026

URL validation failure in Mozilla Thunderbird before 137.0.2 or ESR before 128.9.2 allows remote attackers to leak hashed Windows credentials. The external-attachment handler reads an unvalidated X-Mozilla-External-Attachment-URL to determine file size and follows it when the attachment is clicked. Opening a crafted email can trigger an internal-resource request; on Windows, an SMB file URL can disclose a reusable credential hash.

CVSS severity6.3
Medium
EPSS probability0.27%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

URL validation failure in Mozilla Thunderbird before 137.0.2 or ESR before 128.9.2 allows remote attackers to leak hashed Windows credentials. The external-attachment handler reads an unvalidated X-Mozilla-External-Attachment-URL to determine file size and follows it when the attachment is clicked. Opening a crafted email can trigger an internal-resource request; on Windows, an SMB file URL can disclose a reusable credential hash.

The record

CVE
CVE-2025-3522
Published
Apr 15, 2025
Updated
Apr 13, 2026
Vendor
Unknown vendor
Product
Unknown product
Classifications
CWE-601, T1566.001
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Apr 15, 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

6.3CISA-ADPCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:L/A:L

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-601URL Redirection to Untrusted Site ('Open Redirect')
T1566.001Spearphishing Attachment

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

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Your stack

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