---
id: CVE-2026-109434
title: Sleipnir Browser < 3.9.0 Fullscreen Address Bar Spoofing
summary: >-
  Fenrir Sleipnir Browser for Android before 3.9.0 contains a UI spoofing
  vulnerability that allows remote attackers to impersonate the browser's
  trusted address bar by entering fullscreen mode via the Fullscreen API without
  displaying a p…
severity: medium
cvss: 4.3
cvssVector: 'CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:L/A:N'
cvssSource: cna
cwe:
  - CWE-451
vendor: Fenrir
product: Sleipnir Mobile for Android
affected:
  - sleipnir_mobile_for_android < 3.9.0
ssvc:
  exploitation: none
  automatable: 'no'
  technicalImpact: partial
  timestamp: '2026-10-19T18:36:32.278770Z'
published: '2026-10-19'
updated: '2026-10-19'
sourceUpdated: '2026-10-19T18:36:45.158Z'
source: CVEORG
sourceUrl: 'https://www.cve.org/CVERecord?id=CVE-2026-109434'
references:
  - url: >-
      https://www.fenrir-inc.com/jp/news/2026/10/15/sleipnir-mobile-for-android-3-9-0/
    label: Vendor Advisory
  - url: >-
      https://www.vulncheck.com/advisories/sleipnir-browser-fullscreen-address-bar-spoofing
    label: >-
      VulnCheck Advisory: Sleipnir Browser < 3.9.0 Fullscreen Address Bar
      Spoofing
tags:
  - cve.org
ingestedAt: '2026-10-19T18:35:50.141Z'
---

## Overview

Fenrir Sleipnir Browser for Android before 3.9.0 contains a UI spoofing vulnerability that allows remote attackers to impersonate the browser's trusted address bar by entering fullscreen mode via the Fullscreen API without displaying a persistent notification or trusted-origin indicator. Attackers can render a counterfeit address bar showing a trusted origin over attacker-controlled content after a single user tap, enabling credential harvesting, malware delivery, or social engineering through fake login, update, or payment pages.

## Affected

- `sleipnir_mobile_for_android < 3.9.0`

## Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.