---
id: CVE-2025-1935
title: >-
  A web page could trick a user into setting that site as the default handler
  for a custom URL protocol
summary: >-
  A web page could trick a user into setting that site as the default handler
  for a custom URL protocol. This vulnerability was fixed in Firefox 136,
  Firefox ESR 128.8, Thunderbird 136, and Thunderbird 128.8.
severity: medium
cvss: 4.3
cvssVector: 'CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:N/A:N'
cwe:
  - CWE-79
vendor: mozilla
product: firefox
affected:
  - firefox < 128.8.0
  - firefox < 136.0
  - thunderbird < 128.8.0
  - 'thunderbird >= 129.0, < 136.0'
patched:
  - firefox 136.0
  - thunderbird 136.0
published: '2025-03-04'
updated: '2026-09-30'
sourceUpdated: '2026-09-30T19:10:01.007'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2025-1935'
references:
  - url: 'https://bugzilla.mozilla.org/show_bug.cgi?id=1866661'
    label: security@mozilla.org
  - url: 'https://www.mozilla.org/security/advisories/mfsa2025-14/'
    label: security@mozilla.org
  - url: 'https://www.mozilla.org/security/advisories/mfsa2025-16/'
    label: security@mozilla.org
  - url: 'https://www.mozilla.org/security/advisories/mfsa2025-17/'
    label: security@mozilla.org
  - url: 'https://www.mozilla.org/security/advisories/mfsa2025-18/'
    label: security@mozilla.org
  - url: 'https://lists.debian.org/debian-lts-announce/2025/03/msg00006.html'
    label: af854a3a-2127-422b-91ae-364da2661108
tags:
  - nvd
epss: 0.00343
epssPercentile: 0.25336
ingestedAt: '2026-09-30T19:21:07.228Z'
---

## Overview

A web page could trick a user into setting that site as the default handler for a custom URL protocol. This vulnerability was fixed in Firefox 136, Firefox ESR 128.8, Thunderbird 136, and Thunderbird 128.8.

## Affected

- `firefox < 128.8.0`
- `firefox < 136.0`
- `thunderbird < 128.8.0`
- `thunderbird >= 129.0, < 136.0`

## Remediation

Upgrade past the affected range:

- `firefox 136.0`
- `thunderbird 136.0`