CVE-2026-66064 is a medium-severity (CVSS 5.3) CWE-41 vulnerability in github.com/patrickhener/goshs/v2. A fix is available for github.com/patrickhener/goshs/v2 — see the affected versions and patch details below.
goshs has ACL Bypass & Path Traversal
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-2026-66064.
EPSS Exploitation Probability
Probability of exploitation in the next 30 days, from FIRST.org EPSS.
How urgent is this, really
CVE-2026-66064 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
github.com/patrickhener/goshs/v2🐹goshs.de/goshs/v2🐹github.com/patrickhener/goshs🐹goshs.de/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
sendFile derives the served filename from the raw request path while opening the file from the cleaned path, so appending a trailing slash empties the derived name and defeats both the never-serve rule for the ACL file and the block list.
Finding (Medium): trailing-slash ACL and hidden-file bypass
httpserver/handler.go, sendFile (lines 789-801) takes the filename from the RAW req.URL.Path while the file itself is opened from the filepath.Clean-ed path. The two disagree, and a trailing slash makes the derived name the empty string. Both protections key on that derived name, so both are defeated: the rule that never serves the .goshs ACL file, and the acl.Block list.
Measured, with negative controls:
GET /blocked/secret.txt -> 404 (control, correctly blocked)
GET /blocked/secret.txt/ -> 200 + contents
GET /blocked/.goshs/ -> 200, returns the ACL file itself,
including the admin:$2a$... bcrypt hash
Unauthenticated when the ACL is configured block-only (common usage). Stated precisely: AUTHENTICATION IS NOT BYPASSED. An unauthenticated request against a directory protected by authentication still returns 401 under the same trick; I tested that. The claim is specifically that the block list and the ACL-file protection are bypassed. In-tree evidence that sendFile is the defect: the sibling handlers doDir and bulkDownload both derive the name correctly; sendFile is the lone outlier.
Suggested fixes
- Derive the served filename from the same cleaned path used to open the file, so the authorization decision and the file access cannot disagree.
Tooling
AI assistance was used while investigating. The finding was reproduced against a running server on loopback with negative controls, including the 404-versus-200 pair and the authenticated-directory control that shows authentication is not affected.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐹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/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 | all versions | No fix |
| 🐹Go | goshs.de/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 github.com/patrickhener/goshs/v2, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update github.com/patrickhener/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-2026-66064 is resolved across your whole dependency graph.
Workarounds
Put an independent control in front of the weakness: restrict the affected endpoint or interface to trusted networks, require an additional authentication factor or proxy-level check, and invalidate existing sessions and credentials in case the flaw has already been used.
Frequently Asked Questions
Is CVE-2026-66064 in your dependencies?
Find it across Go, including transitive dependencies.