CVE-2025-4086: 
Mozilla Firefox vulnerability analysis and mitigation

CVE-2025-4086 is a security vulnerability affecting Thunderbird for Android versions prior to 138. The vulnerability was discovered by a researcher named Hafiizh and was disclosed on April 29, 2025. The issue involves a specially crafted filename containing a large number of encoded newline characters that could obscure the file's extension when displayed in the download dialog (Mozilla Advisory).

The vulnerability has been assigned a moderate severity rating with a CVSS v3.1 base score of 6.5 (MEDIUM). The vulnerability is classified under CWE-451 (User Interface (UI) Misrepresentation of Critical Information). The attack vector is network-based (AV:N) with low attack complexity (AC:L), requiring no privileges (PR:N) and no user interaction (UI:N). The scope is unchanged (S:U) with low impacts on confidentiality (C:L) and integrity (I:L), and no impact on availability (A:N) (NVD).

The vulnerability could allow attackers to obscure the true file extension of downloaded files, potentially leading to users executing malicious files under the assumption they are of a different, benign type. This type of misrepresentation could facilitate social engineering attacks or malware distribution (CIS Advisory).

The vulnerability has been fixed in Thunderbird version 138. Users are advised to update their Thunderbird for Android installations to this version or later. No specific workarounds have been published for users who cannot immediately update (Mozilla Advisory).