# CVE-2021-20835: Missing authorization in Android App 'Mercari (Merpay) - Marketplace and Mobile Payments App' (Japan version)

> A remote attacker can trick users into launching arbitrary activities via a custom URL scheme, potentially stealing Mercari account access tokens.

- **Severity:** High 7.5 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 24 Nov 2021
- **Updated:** 3 Aug 2024
- **Also known as:** GHSA-2hf9-98xv-3h7h

## What is CVE-2021-20835?

CVE-2021-20835 is a high-severity missing authorization vulnerability in Mercari, Inc. Android App 'Mercari (Merpay) - Marketplace and Mobile Payments App' (Japan version), published on 24 Nov 2021. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

Improper authorization in handler for custom URL scheme vulnerability in Android App 'Mercari (Merpay) - Marketplace and Mobile Payments App' (Japan version) versions prior to 4.49.1 allows a remote attacker to lead a user to access an arbitrary website and the website launches an arbitrary Activity of the app via the vulnerable App, which may result in Mercari account's access token being obtained.

Weakness: CWE-862 (Missing Authorization)

## Which versions are affected by CVE-2021-20835?

It affects 1 product.


Products: Mercari Mercari.

## How do I fix CVE-2021-20835?

No fix has been published for CVE-2021-20835 yet. Limit exposure of the affected software until one is available.

## Is CVE-2021-20835 being exploited?

There is no known exploitation of CVE-2021-20835 in the wild and no public exploit code.

## Other vulnerabilities in Mercari, Inc. Android App 'Mercari (Merpay) - Marketplace and Mobile Payments App' (Japan version)

- [CVE-2020-5604](https://insights.sbomify.com/CVE-2020-5604/): Code injection in Android App 'Mercari' (Japan version) (high 8.1)
- [CVE-2024-23388](https://insights.sbomify.com/CVE-2024-23388/): Open redirect in "Mercari" App for Android (medium 6.1)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2021-20835 and fix it if it is affected.

What it is: CVE-2021-20835 is a high-severity missing authorization vulnerability in Mercari, Inc. Android App 'Mercari (Merpay) - Marketplace and Mobile Payments App' (Japan version), published on 24 Nov 2021. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2021-20835 in the wild and no public exploit code.

Affected product: Mercari, Inc. Android App 'Mercari (Merpay) - Marketplace and Mobile Payments App' (Japan version). 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-2021-20835/ (Markdown: https://insights.sbomify.com/CVE-2021-20835/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-20835
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-20835
- OSV: https://osv.dev/vulnerability/CVE-2021-20835

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From sbomify Insights: https://insights.sbomify.com/CVE-2021-20835/
Summaries are generated and may contain mistakes; the official description above is the record.