CVE-2022-21221 is a medium-severity (CVSS 5.9) Path Traversal vulnerability in github.com/valyala/fasthttp. 2 public exploit references exist, so weaponization risk is real. A fix is available for github.com/valyala/fasthttp — see the affected versions and patch details below.
Directory Traversal
EPSS Exploitation Probability
Probability of exploitation in the next 30 days, from FIRST.org EPSS.
How urgent is this, really
CVE-2022-21221 by exploitation likelihood (EPSS) against impact (CVSS). Outside the shaded patch-first corner.
Where this sits among everything scored
Of 385,738 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Counts from FIRST.org, log-scaled.
Real-World Exposure
github.com/valyala/fasthttpReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects Go packages — download data is not available via public APIs for these ecosystems.
Description
The package github.com/valyala/fasthttp before 1.34.0 are vulnerable to Directory Traversal via the ServeFile function, due to improper sanitization. It is possible to be exploited by using a backslash %5c character in the path. Note: This security issue impacts Windows users only.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐹Go | github.com/valyala/fasthttp | all versions | 1.34.0go get github.com/valyala/fasthttp@v1.34.0 |
Affected Products
fasthttpfasthttp_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 github.com/valyala/fasthttp, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update github.com/valyala/fasthttp to 1.34.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2022-21221 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-2022-21221 in your dependencies?
Find it across Go, including transitive dependencies.