CVE-2021-32842 — SharpZipLib
MEDIUMCVE-2021-32842 is a medium-severity (CVSS 5.3) Path Traversal vulnerability in SharpZipLib. 1 public exploit reference exists, so weaponization risk is real. A fix is available for SharpZipLib — see the affected versions and patch details below.
Path Traversal in SharpZipLib
Exploitation Status
Proof-of-concept exploit code exists
- CISA’s SSVC triage found public proof-of-concept exploit code for this CVE, though no confirmed active exploitation.
Exploitation and automatability from CISA’s SSVC triage for CVE-2021-32842.
EPSS Exploitation Probability
Probability of exploitation in the next 30 days, from FIRST.org EPSS.
How urgent is this, really
CVE-2021-32842 by exploitation likelihood (EPSS) against impact (CVSS). Outside the shaded patch-first corner.
Where this sits among everything scored
Of 385,386 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Counts from FIRST.org, log-scaled.
Real-World Exposure
SharpZipLibReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects NuGet packages — download data is not available via public APIs for these ecosystems.
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.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| .NETNuGet | SharpZipLib | ≥ 1.0.0&&< 1.3.3 | 1.3.3dotnet add package SharpZipLib --version 1.3.3 |
Affected Products
sharpziplibsharpziplib_projectResearch use only. For defensive security, authorized penetration testing, and academic research only. Never execute exploit code against systems without explicit written authorization.
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for SharpZipLib, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update SharpZipLib to 1.3.3 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2021-32842 is resolved across your whole dependency graph.
Workarounds
Resolve every user-supplied path to its canonical form and reject anything that escapes the intended directory, and run the component under an account that has no read or write access outside the directory it legitimately serves.
Frequently Asked Questions
Is CVE-2021-32842 in your dependencies?
Find it across NuGet, including transitive dependencies.