CVE-2025-5986Network attack vector

Disk exhaustion via concealed mailbox link downloads

Published Jun 11, 2025 · Updated Apr 13, 2026

Improper link handling in Thunderbird 128 ESR before 128.11.1 and Thunderbird 139 before 139.0.2 allows remote attackers to trigger downloads. Crafted mailbox:/// links in HTML email bypass the download prompt and auto-saving preference, while visual obfuscation conceals the trigger. The email must be viewed in HTML mode and the link activated; repeated Linux downloads can exhaust disk space and interrupt service.

CVSS severity6.5
Medium
EPSS probability0.58%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Improper link handling in Thunderbird 128 ESR before 128.11.1 and Thunderbird 139 before 139.0.2 allows remote attackers to trigger downloads. Crafted mailbox:/// links in HTML email bypass the download prompt and auto-saving preference, while visual obfuscation conceals the trigger. The email must be viewed in HTML mode and the link activated; repeated Linux downloads can exhaust disk space and interrupt service.

The record

CVE
CVE-2025-5986
Published
Jun 11, 2025
Updated
Apr 13, 2026
Vendor
Unknown vendor
Product
Unknown product
Classifications
CWE-451, T1204.001
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jun 11, 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

6.5CISA ADPCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H

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 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-451User Interface (UI) Misrepresentation of Critical Information
T1204.001User Execution: Malicious Link

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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