# CVE-2021-37632: Deserialization of Untrusted Data in com.supermartijn642.configlib.ConfigSyncPacket

> An attacker can achieve remote code execution by sending malicious packets to Minecraft servers or clients using the vulnerable Config Lib library.

- **Severity:** High 8.1 (`CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 5 Aug 2021
- **Updated:** 4 Aug 2024

## What is CVE-2021-37632?

CVE-2021-37632 is a high-severity unsafe deserialization vulnerability in SuperMartijn642sConfigLib, published on 5 Aug 2021. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

SuperMartijn642's Config Lib is a library used by a number of mods for the game Minecraft. The versions of SuperMartijn642's Config Lib between 1.0.4 and 1.0.8 are affected by a vulnerability and can be exploited on both servers and clients. Using SuperMartijn642's Config Lib, servers will send a packet to clients with the server's config values. In order to read `enum` values from the packet data, `ObjectInputStream#readObject` is used. `ObjectInputStream#readObject` will instantiate a class based on the input data. Since, the packet data is not validated before `ObjectInputStream#readObject` is called, an attacker can instantiate any class by sending a malicious packet. If a suitable class is found, the vulnerability can lead to a number of exploits, including remote code execution. Although the vulnerable packet is typically only send from server to client, it can theoretically also be send from client to server. This means both clients and servers running SuperMartijn642's Config Lib between 1.0.4 and 1.0.8 are vulnerable. The vulnerability has been patched in SuperMartijn642's Config lib 1.0.9. Both, players and server owners, should update to 1.0.9 or higher.

Weakness: CWE-502 (Deserialization of Untrusted Data)

## Which versions are affected by CVE-2021-37632?

It affects 1 product.


Products: Config Lib Project Config Lib.

## How do I fix CVE-2021-37632?

No fix has been published for CVE-2021-37632 yet. Limit exposure of the affected software until one is available.

## Is CVE-2021-37632 being exploited?

There is no known exploitation of CVE-2021-37632 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2021-37632 and fix it if it is affected.

What it is: CVE-2021-37632 is a high-severity unsafe deserialization vulnerability in SuperMartijn642sConfigLib, published on 5 Aug 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-2021-37632 in the wild and no public exploit code.

Affected product: SuperMartijn642sConfigLib. 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-2021-37632/ (Markdown: https://insights.sbomify.com/CVE-2021-37632/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-37632
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-37632
- OSV: https://osv.dev/vulnerability/CVE-2021-37632

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From sbomify Insights: https://insights.sbomify.com/CVE-2021-37632/
Summaries are generated and may contain mistakes; the official description above is the record.