CVE-2026-66063 is a medium-severity (CVSS 6.5) Path Traversal vulnerability in goshs.de/goshs/v2. A fix is available for goshs.de/goshs/v2 — see the affected versions and patch details below.
goshs has a Path Traversal issue
Exploitation Status
No confirmed exploitation observed yet
- CISA assesses this as automatable — exploitation doesn’t require manual, per-target effort, which raises the odds of mass scanning and opportunistic attacks.
- CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.
Exploitation and automatability from CISA’s SSVC triage for CVE-2026-66063.
EPSS Exploitation Probability
Probability of exploitation in the next 30 days, from FIRST.org EPSS.
How urgent is this, really
CVE-2026-66063 by exploitation likelihood (EPSS) against impact (CVSS). Outside the shaded patch-first corner.
Where this sits among everything scored
Of 383,485 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Counts from FIRST.org, log-scaled.
Real-World Exposure
goshs.de/goshs/v2🐹github.com/patrickhener/goshs/v2🐹goshs.de/goshs🐹github.com/patrickhener/goshsReal-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
Summary
The multipart upload filename fix splits on the path separator but never rejects dot-dot, allowing a write outside the served tree.
Finding (Medium): upload filename escapes the served tree (residual of CVE-2026-35393)
The multipart filename fix (updown.go lines 135-136) splits on the path separator but never rejects "..". Uploading with filename=".." results in os.Create against the parent of the upload folder with a trailing marker character, outside the served tree, and the subsequent failed rename leaves that file behind. Verified: a file containing ESCAPED_WRITE_PROOF was written outside the webroot, unauthenticated, with the default configuration. Not claimed: a Windows-specific variant (Go's Part.FileName() already applies filepath.Base).
Suggested fixes
- Reject any upload filename that is "..", is empty after sanitisation, or resolves outside the upload folder; validate the final resolved destination rather than only transforming the input.
Tooling
AI assistance was used while investigating. The finding was reproduced against a running server on loopback.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐹Go | goshs.de/goshs/v2 | all versions | 2.1.5-0.20260727065949-f3ef599e4091go get goshs.de/goshs/v2@v2.1.5-0.20260727065949-f3ef599e4091 |
| 🐹Go | github.com/patrickhener/goshs/v2 | all versions | 2.1.5-0.20260727065949-f3ef599e4091go get github.com/patrickhener/goshs/v2@v2.1.5-0.20260727065949-f3ef599e4091 |
| 🐹Go | goshs.de/goshs | all versions | No fix |
| 🐹Go | github.com/patrickhener/goshs | all versions | No fix |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for goshs.de/goshs/v2, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update goshs.de/goshs/v2 to 2.1.5-0.20260727065949-f3ef599e4091 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-66063 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-2026-66063 in your dependencies?
Find it across Go, including transitive dependencies.