# CVE-2021-29437: Account compromise by man-in-the-middle attack

> Attackers can hijack user accounts by tricking users into posting login codes, granting full access to user data and actions.

- **Severity:** High 8.0 (`CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:C/C:H/I:H/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:** 13 Apr 2021
- **Updated:** 3 Aug 2024
- **Also known as:** GHSA-gvpg-23fh-8g75

## What is CVE-2021-29437?

CVE-2021-29437 is a high-severity authentication bypass vulnerability in ScratchVerifier ScratchOAuth2, published on 13 Apr 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

ScratchOAuth2 is an Oauth implementation for Scratch. Any ScratchOAuth2-related data normally accessible and modifiable by a user can be read and modified by a third party. 1. Scratch user visits 3rd party site. 2. 3rd party site asks user for Scratch username. 3. 3rd party site pretends to be user and gets login code from ScratchOAuth2. 4. 3rd party site gives code to user and instructs them to post it on their profile. 5. User posts code on their profile, not knowing it is a ScratchOAuth2 login code. 6. 3rd party site completes login with ScratchOAuth2. 7. 3rd party site has full access to anything the user could do if they directly logged in. See referenced GitHub security advisory for patch notes and workarounds.

Weakness: CWE-863 (Incorrect Authorization)

## Which versions are affected by CVE-2021-29437?

It affects 1 product.


Products: Scratchoauth2 Project Scratchoauth2.

## How do I fix CVE-2021-29437?

No fix has been published for CVE-2021-29437 yet. Limit exposure of the affected software until one is available.

## Is CVE-2021-29437 being exploited?

There is no known exploitation of CVE-2021-29437 in the wild and no public exploit code.

## Other vulnerabilities in ScratchVerifier ScratchOAuth2

- [CVE-2021-46250](https://insights.sbomify.com/CVE-2021-46250/): Auth bypass in n/a (critical 10.0)
- [CVE-2021-46249](https://insights.sbomify.com/CVE-2021-46249/): Auth bypass in n/a (medium 6.5)
- [CVE-2021-46251](https://insights.sbomify.com/CVE-2021-46251/): Cross-site scripting in n/a (medium 6.1)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2021-29437 and fix it if it is affected.

What it is: CVE-2021-29437 is a high-severity authentication bypass vulnerability in ScratchVerifier ScratchOAuth2, published on 13 Apr 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-2021-29437 in the wild and no public exploit code.

Affected product: ScratchVerifier ScratchOAuth2. 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-2021-29437/ (Markdown: https://insights.sbomify.com/CVE-2021-29437/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-29437
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-29437
- OSV: https://osv.dev/vulnerability/CVE-2021-29437

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-29437/
Summaries are generated and may contain mistakes; the official description above is the record.