# CVE-2021-23521: Link Following

> Attackers can execute arbitrary code or modify files by crafting a malicious archive with symbolic links that are followed during extraction.

- **Severity:** Medium 5.5 (`CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 31 Jan 2022
- **Updated:** 17 Sep 2024
- **Also known as:** DEBIAN-CVE-2021-23521, GHSA-cv9m-jw92-c3v3, SNYK-UNMANAGED-JUCEFRAMEWORKJUCE-2388608, UBUNTU-CVE-2021-23521

## What is CVE-2021-23521?

CVE-2021-23521 is a medium-severity path traversal vulnerability in n/a, published on 31 Jan 2022. It can only be exploited from the same machine or local network, with no action from the victim.

### Official description

This affects the package juce-framework/JUCE before 6.1.5. This vulnerability is triggered when a malicious archive is crafted with an entry containing a symbolic link. When extracted, the symbolic link is followed outside of the target dir allowing writing arbitrary files on the target host. In some cases, this can allow an attacker to execute arbitrary code. The vulnerable code is in the ZipFile::uncompressEntry function in juce_ZipFile.cpp and is executed when the archive is extracted upon calling uncompressTo() on a ZipFile object.

Weakness: CWE-59 (Improper Link Resolution Before File Access)

## Which versions are affected by CVE-2021-23521?

It affects 1 product.


Products: Juce Juce.

## How do I fix CVE-2021-23521?

Upgrade to a fixed version.

## Is CVE-2021-23521 being exploited?

There is no known exploitation of CVE-2021-23521 in the wild and no public exploit code.

## Other vulnerabilities in n/a

- [CVE-2021-23520](https://insights.sbomify.com/CVE-2021-23520/): Arbitrary File Write via Archive Extraction (Zip Slip) (medium 5.5)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2021-23521 and fix it if it is affected.

What it is: CVE-2021-23521 is a medium-severity path traversal vulnerability in n/a, published on 31 Jan 2022. It can only be exploited from the same machine or local network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2021-23521 in the wild and no public exploit code.

Affected product: n/a. 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-2021-23521/ (Markdown: https://insights.sbomify.com/CVE-2021-23521/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-23521
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-23521
- OSV: https://osv.dev/vulnerability/CVE-2021-23521

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-23521/
Summaries are generated and may contain mistakes; the official description above is the record.