---
id: CVE-2025-4086
title: >-
  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
summary: >-
  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
  …
severity: medium
cvss: 6.5
cvssVector: 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N'
cwe:
  - CWE-451
vendor: mozilla
product: firefox
affected:
  - firefox < 138.0
  - thunderbird < 138.0
patched:
  - firefox 138.0
  - thunderbird 138.0
published: '2025-04-29'
updated: '2026-09-30'
sourceUpdated: '2026-09-30T18:10:00.190'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2025-4086'
references:
  - url: 'https://bugzilla.mozilla.org/show_bug.cgi?id=1945705'
    label: security@mozilla.org
  - url: 'https://www.mozilla.org/security/advisories/mfsa2025-28/'
    label: security@mozilla.org
  - url: 'https://www.mozilla.org/security/advisories/mfsa2025-31/'
    label: security@mozilla.org
tags:
  - nvd
epss: 0.0029
epssPercentile: 0.19479
ingestedAt: '2026-09-30T18:17:24.434Z'
---

## Overview

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

- `firefox < 138.0`
- `thunderbird < 138.0`

## Remediation

Upgrade past the affected range:

- `firefox 138.0`
- `thunderbird 138.0`