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

> Attackers can spoof the address bar in fullscreen mode to trick users into revealing credentials or installing malware on Sleipnir Browser for Android.

- **Severity:** Medium 5.1 (`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`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** A user has to click or open something
- **Fix available:** No
- **Published:** 19 Oct 2026
- **Updated:** 19 Oct 2026
- **Also known as:** GHSA-6cmm-rr3r-h5xv

## What is CVE-2026-109434?

CVE-2026-109434 is a medium-severity vulnerability in Fenrir Sleipnir Mobile for Android, published on 19 Oct 2026. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.

### Official 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.

Weakness: CWE-451 (User Interface (UI) Misrepresentation of Critical Information)

## Which versions are affected by CVE-2026-109434?


## How do I fix CVE-2026-109434?

No fix has been published for CVE-2026-109434 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-109434 being exploited?

There is no known exploitation of CVE-2026-109434 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-109434 and fix it if it is affected.

What it is: CVE-2026-109434 is a medium-severity vulnerability in Fenrir Sleipnir Mobile for Android, published on 19 Oct 2026. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.
Exploitation: There is no known exploitation of CVE-2026-109434 in the wild and no public exploit code.

Affected product: Fenrir Sleipnir Mobile for Android. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-109434/ (Markdown: https://insights.sbomify.com/CVE-2026-109434/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-109434
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-109434
- OSV: https://osv.dev/vulnerability/CVE-2026-109434

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-109434/
Summaries are generated and may contain mistakes; the official description above is the record.