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MEDIUM

Unsolicited File Download, Disk Space Exhaustion, and Credential Leakage via mailbox:/// Links

Published Jun 11, 2025

Description

A crafted HTML email using mailbox:/// links can trigger automatic, unsolicited downloads of .pdf files to the user's desktop or home directory without prompting, even if auto-saving is disabled. This behavior can be abused to fill the disk with garbage data (e.g. using /dev/urandom on Linux) or to leak Windows credentials via SMB links when the email is viewed in HTML mode. While user interaction is required to download the .pdf file, visual obfuscation can conceal the download trigger. Viewing the email in HTML mode is enough to load external content. This vulnerability was fixed in Thunderbird 128.11.1 and Thunderbird 139.0.2.

Affected products

Remediation

Red Hat statement

Red Hat Product Security rates the severity of this flaw as determined by the Mozilla Foundation Security Advisory.

Metrics

Weaknesses (2)

CWE-400

Uncontrolled Resource Consumption

CWE-451

References (9)

Change history (0)

No recorded changes yet.

Sources
CVE.org / MITRE
Status PUBLISHED
Assigner mozilla
Published Jun 11, 2025
Updated Apr 13, 2026
Reserved Jun 10, 2025
Link CVE-2025-5986
CISA Vulnrichment
Updated Jun 11, 2025
NVD
Status Modified
Modified Jun 17, 2026
Link CVE-2025-5986
Red Hat
Severity Important
Public date Jun 10, 2025
Links CVE-2025-5986 - Bugzilla