# CVE-2021-32842: Path Traversal in SharpZipLib

> An attacker can create files outside the intended directory due to missing slash validation in SharpZipLib, potentially overwriting files.

- **Severity:** Medium 4.0 (`CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 26 Jan 2022
- **Updated:** 22 Apr 2025
- **Also known as:** GHSA-mm6g-mmq6-53ff, UBUNTU-CVE-2021-32842

## What is CVE-2021-32842?

CVE-2021-32842 is a medium-severity path traversal vulnerability in icsharpcode sharpziplib, published on 26 Jan 2022. It can only be exploited from the same machine or local network, with no action from the victim.

### Official description

SharpZipLib (or #ziplib) is a Zip, GZip, Tar and BZip2 library. Starting version 1.0.0 and prior to version 1.3.3, a check was added if the destination file is under a destination directory. However, it is not enforced that `_baseDirectory` ends with slash. If the _baseDirectory 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. Version 1.3.3 fixed this vulnerability.

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

## Which versions are affected by CVE-2021-32842?

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


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `SharpZipLib` | NuGet | From 1.0.0 | 1.3.3 |
| `SharpZipLib` | NuGet | From 1.0.0 | 1.3.3 |

Products: Sharpziplib Project Sharpziplib.

## How do I fix CVE-2021-32842?

Upgrade SharpZipLib to 1.3.3 or later.

## Is CVE-2021-32842 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2021-32842 exists.

## Other vulnerabilities in icsharpcode sharpziplib

- [CVE-2021-32840](https://insights.sbomify.com/CVE-2021-32840/): Path Traversal in SharpZipLib (high 7.3)
- [CVE-2018-1002208](https://insights.sbomify.com/CVE-2018-1002208/): Improper Limitation of a Pathname to a Restricted Directory in SharpZipLib (medium 5.5)
- [CVE-2021-32841](https://insights.sbomify.com/CVE-2021-32841/): Path Traversal in SharpZipLib (medium 4.0)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2021-32842 and fix it if it is affected.

What it is: CVE-2021-32842 is a medium-severity path traversal vulnerability in icsharpcode sharpziplib, published on 26 Jan 2022. It can only be exploited from the same machine or local network, with no action from the victim.
Exploitation: It is not confirmed as exploited in the wild, but public exploit code for CVE-2021-32842 exists.

Affected packages and fixed versions:
- SharpZipLib (NuGet): affected from 1.0.0; fixed in 1.3.3
- SharpZipLib (NuGet): affected from 1.0.0; fixed in 1.3.3

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-2021-32842/ (Markdown: https://insights.sbomify.com/CVE-2021-32842/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-32842
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-32842
- OSV: https://osv.dev/vulnerability/CVE-2021-32842

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-32842/
Summaries are generated and may contain mistakes; the official description above is the record.