# CVE-2021-39208: WriteEntryToDirectory used for an archive extraction is vulnerable to partial path traversal.

> Attackers can create files outside the intended directory if ExtractFullPath is enabled and the destination path lacks a trailing slash.

- **Severity:** Medium 4.3 (`CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:L/A:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 16 Sep 2021
- **Updated:** 4 Aug 2024
- **Also known as:** ECHO-f206-fe3f-2dda, GHSA-jp7f-grcv-6mjf

## What is CVE-2021-39208?

CVE-2021-39208 is a medium-severity path traversal vulnerability in adamhathcock sharpcompress, published on 16 Sep 2021. Any signed-in user can exploit it over the network, with no action from the victim.

### Official description

SharpCompress is a fully managed C# library to deal with many compression types and formats. Versions prior to 0.29.0 are vulnerable to partial path traversal. SharpCompress recreates a hierarchy of directories under destinationDirectory if ExtractFullPath is set to true in options. In order to prevent extraction outside the destination directory the destinationFileName path is verified to begin with fullDestinationDirectoryPath. However, prior to version 0.29.0, it is not enforced that fullDestinationDirectoryPath ends with slash. If the destinationDirectory is not slash terminated like `/home/user/dir` it is possible to create a file with a name thats begins as the destination directory one level up from the directory, i.e. `/home/user/dir.sh`. Because of the file name and destination directory constraints the arbitrary file creation impact is limited and depends on the use case. This issue is fixed in SharpCompress version 0.29.0.

Weakness: CWE-22 (Improper Limitation of a Pathname to a Restricted Directory)

## Which versions are affected by CVE-2021-39208?

2 open source packages ship an affected version, including SharpCompress. It affects 1 product.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `SharpCompress` | NuGet | All versions | 0.29 |
| `SharpCompress` | NuGet | All versions | 0.29 |

Products: Sharpcompress Project Sharpcompress.

## How do I fix CVE-2021-39208?

Upgrade SharpCompress to 0.29 or later.

## Is CVE-2021-39208 being exploited?

There is no known exploitation of CVE-2021-39208 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2021-39208 and fix it if it is affected.

What it is: CVE-2021-39208 is a medium-severity path traversal vulnerability in adamhathcock sharpcompress, published on 16 Sep 2021. Any signed-in user can exploit it over the network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2021-39208 in the wild and no public exploit code.

Affected packages and fixed versions:
- SharpCompress (NuGet): affected all versions; fixed in 0.29
- SharpCompress (NuGet): affected all versions; fixed in 0.29

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-2021-39208/ (Markdown: https://insights.sbomify.com/CVE-2021-39208/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-39208
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-39208
- OSV: https://osv.dev/vulnerability/CVE-2021-39208

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-39208/
Summaries are generated and may contain mistakes; the official description above is the record.