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

Severity: medium (CVSS 4.3 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.3% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2026-10-19 · updated 2026-10-19
Weakness: CWE-451

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.

Affected products

Fenrir Sleipnir Mobile for Android: before 3.9.0 — fixed in 3.9.0

How to fix

Upgrade to a fixed version: Fenrir Sleipnir Mobile for Android 3.9.0. Check the vendor advisory for mitigations.

References

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