# CVE-2021-20777: Missing authorization in GU App for Android

> A remote attacker can trick users into accessing arbitrary websites via the app's custom URL scheme due to improper authorization checks.

- **Severity:** Medium 4.3 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:L/A: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:** 7 Jul 2021
- **Updated:** 3 Aug 2024
- **Also known as:** GHSA-q6p4-2q7c-4vw7

## What is CVE-2021-20777?

CVE-2021-20777 is a medium-severity missing authorization vulnerability in G.U. CO., LTD. GU App for Android, published on 7 Jul 2021. 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

Improper authorization in handler for custom URL scheme vulnerability in GU App for Android versions from 4.8.0 to 5.0.2 allows a remote attacker to lead a user to access an arbitrary website via the vulnerable App.

Weakness: CWE-862 (Missing Authorization)

## Which versions are affected by CVE-2021-20777?

It affects 1 product.


Products: Gu-Global Gu.

## How do I fix CVE-2021-20777?

No fix has been published for CVE-2021-20777 yet. Limit exposure of the affected software until one is available.

## Is CVE-2021-20777 being exploited?

There is no known exploitation of CVE-2021-20777 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2021-20777 and fix it if it is affected.

What it is: CVE-2021-20777 is a medium-severity missing authorization vulnerability in G.U. CO., LTD. GU App for Android, published on 7 Jul 2021. 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-2021-20777 in the wild and no public exploit code.

Affected product: G.U. CO., LTD. GU App 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-2021-20777/ (Markdown: https://insights.sbomify.com/CVE-2021-20777/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-20777
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-20777
- OSV: https://osv.dev/vulnerability/CVE-2021-20777

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-20777/
Summaries are generated and may contain mistakes; the official description above is the record.