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

What is CVE-2025-4086?

CVE-2025-4086 is a medium-severity vulnerability in Mozilla Firefox, published on 29 Apr 2025. An attacker can exploit it over the internet without logging in, with no action from the victim.

Official 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.

Weakness: CWE-451

Which versions are affected by CVE-2025-4086?

It affects 2 products.

Products include Mozilla Firefox, Mozilla Thunderbird.

How do I fix CVE-2025-4086?

Upgrade to a fixed version.

Is CVE-2025-4086 being exploited?

There is no known exploitation of CVE-2025-4086 in the wild and no public exploit code.

Other vulnerabilities in Mozilla Firefox

• CVE-2019-11708 Mozilla Firefox and Thunderbird Sandbox Escape Exploited Critical 10.0
• CVE-2010-3765 Mozilla Multiple Products Remote Code Execution Exploited Critical 9.8
• CVE-2022-26486 Mozilla Firefox Use-After-Free Exploited Critical 9.6
• CVE-2022-26485 Mozilla Firefox Use-After-Free Exploited High 8.8
• CVE-2019-11707 Mozilla Firefox and Thunderbird Type Confusion Exploited High 8.8

All Mozilla Firefox vulnerabilities

Sources

• CVE record
• NVD
• OSV
• GitHub advisory
• How this page is made

Also known as GHSA-54jr-pmx4-5pvr.