What’s Vulnerable › Vulnerabilities

CVE-2025-4086: Specially crafted filename could be used to obscure download type

• Severity: medium (CVSS 6.5 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.3% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2025-04-29 · updated 2026-09-30
• Weakness: CWE-451

Description

A specially crafted filename containing a large number of encoded newline characters could obscure the file's extension when displayed in the download dialog. *This bug only affects Thunderbird for Android. Other versions of Thunderbird are unaffected.*. This vulnerability was fixed in Firefox 138 and Thunderbird 138.

Affected products

• Mozilla Firefox: before 138.0 — fixed in 138.0
• Mozilla Thunderbird: before 138.0 — fixed in 138.0

How to fix

Upgrade to a fixed version: Mozilla Firefox 138.0; Mozilla Thunderbird 138.0. Check the vendor advisory for mitigations.

References

• https://bugzilla.mozilla.org/show_bug.cgi?id=1945705
• https://www.mozilla.org/security/advisories/mfsa2025-28/
• https://www.mozilla.org/security/advisories/mfsa2025-31/

Get alerted when CVE-2025-4086 or the next vulnerability affects your stack