CVE-2025-3932Network attack vector

Message-activity disclosure via attachment tracking link

Published May 14, 2025 · Updated Apr 13, 2026

Information disclosure in Mozilla Thunderbird before 128.10.1 and 129.0 through 138.0 allows remote attackers to confirm message activity. The attachment handler follows a web URL supplied in the X-Mozilla-External-Attachment-URL header even when remote content is blocked. The recipient must open the displayed attachment; doing so contacts the attacker's tracking endpoint and reveals that the message was viewed.

CVSS severity6.5
Medium
EPSS probability0.37%
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

Information disclosure in Mozilla Thunderbird before 128.10.1 and 129.0 through 138.0 allows remote attackers to confirm message activity. The attachment handler follows a web URL supplied in the X-Mozilla-External-Attachment-URL header even when remote content is blocked. The recipient must open the displayed attachment; doing so contacts the attacker's tracking endpoint and reveals that the message was viewed.

The record

CVE
CVE-2025-3932
Published
May 14, 2025
Updated
Apr 13, 2026
Vendor
Unknown vendor
Product
Unknown product
Classifications
CWE-288, T1566.001
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. May 14, 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

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

6.5CISA-ADPCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/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 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-288Authentication Bypass Using an Alternate Path or Channel
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

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