CVE-2021-32840 is a critical-severity (CVSS 9.8) 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-2021-32840.
EPSS Exploitation Probability
Probability of exploitation in the next 30 days, from FIRST.org EPSS.
How urgent is this, really
CVE-2021-32840 by exploitation likelihood (EPSS) against impact (CVSS). Outside the shaded patch-first corner.
Where this sits among everything scored
Of 385,987 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. Prior to version 1.3.3, a TAR file entry ../evil.txt may be extracted in the parent directory of destFolder. This leads to arbitrary file write that may lead to code execution. The vulnerability was patched in version 1.3.3.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| .NETNuGet | SharpZipLib | all versions | 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-2021-32840 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-2021-32840 in your dependencies?
Find it across NuGet, including transitive dependencies.