Sc File Upload

SC: Insecure File Upload

Purpose

Detects insecure file upload vulnerabilities including unrestricted file type uploads, MIME type vs extension mismatches, double extension bypasses, executable uploads to web-accessible directories, missing file size limits, and archive extraction attacks. Focuses on upload endpoints that could lead to remote code execution or stored XSS.

Activation

Called by sc-orchestrator during Phase 2 when file upload functionality is detected.

Phase 1: Discovery

Keyword Patterns to Search

"multer", "upload", "multipart", "formidable", "busboy",
"FileUpload", "IFormFile", "MultipartFile", "@RequestPart",
"$_FILES", "move_uploaded_file", "UploadedFile",
"file.save(", "storage.upload(", "putObject("

Vulnerability Patterns

1. No File Type Validation:

// VULNERABLE: Accept any file
const upload = multer({ dest: 'public/uploads/' });
app.post('/upload', upload.single('file'), (req, res) => {
  res.json({ path: `/uploads/${req.file.filename}` });
});

// SAFE: Validate file type
const upload = multer({
  dest: 'uploads/',  // NOT in public directory
  fileFilter: (req, file, cb) => {
    const allowed = ['image/jpeg', 'image/png', 'image/gif'];
    if (allowed.includes(file.mimetype)) {
      cb(null, true);
    } else {
      cb(new Error('Invalid file type'), false);
    }
  },
  limits: { fileSize: 5 * 1024 * 1024 }  // 5MB limit
});

2. Upload to Webroot:

// VULNERABLE: Upload directly to web-accessible directory
move_uploaded_file($_FILES['file']['tmp_name'], 'public/uploads/' . $_FILES['file']['name']);
// If user uploads evil.php → accessible at /uploads/evil.php → RCE!

// SAFE: Upload outside webroot + rename
$ext = pathinfo($_FILES['file']['name'], PATHINFO_EXTENSION);
$allowed = ['jpg', 'png', 'gif'];
if (!in_array(strtolower($ext), $allowed)) { die('Invalid type'); }
$newName = bin2hex(random_bytes(16)) . '.' . $ext;
move_uploaded_file($_FILES['file']['tmp_name'], '/var/data/uploads/' . $newName);

Checks

1. Is file type validated server-side (not just client-side)?
2. Are files stored outside the web root?
3. Are filenames sanitized and randomized?
4. Is file size limited?
5. Are magic bytes checked (not just extension/MIME)?
6. Is the upload directory configured to not execute scripts?

Severity Classification

• Critical: Unrestricted upload to webroot enabling RCE (PHP, JSP, ASPX)
• High: Upload allowing XSS (SVG, HTML) or bypassing type checks
• Medium: Missing file size limits (DoS), client-side-only validation
• Low: Upload configuration weaknesses without clear exploitation path

Output Format

Finding: UPLOAD-{NNN}

• Title: Insecure File Upload in {endpoint}
• Severity: Critical | High | Medium | Low
• Confidence: 0-100
• File: file/path:line
• Vulnerability Type: CWE-434 (Unrestricted Upload of File with Dangerous Type)
• Description: File upload at {endpoint} lacks {validation type}.
• Impact: Remote code execution, stored XSS, denial of service.
• Remediation: Validate file type server-side, store outside webroot, randomize filenames, set size limits.
• References: https://cwe.mitre.org/data/definitions/434.html

Common False Positives

1. Cloud storage uploads — files uploaded to S3/GCS are not directly executable
2. Image processing pipelines — files processed through ImageMagick/Sharp before storage
3. API payload uploads — JSON/XML payloads parsed as data, not stored as files