security: validate CDP URLs to prevent SSRF (V-010, CVSS 8.4)

Add URL validation before fetching Chrome DevTools Protocol endpoints.
Only allows localhost and private network addresses.

Changes:
- tools/browser_tool.py: Add hostname validation in _resolve_cdp_override()
- Block external URLs to prevent SSRF attacks
- Log security errors for rejected URLs

CVSS: 8.4 (High)
Refs: V-010 in SECURITY_AUDIT_REPORT.md
CWE-918: Server-Side Request Forgery

tools/browser_tool.py

@@ -170,6 +170,9 @@ def _resolve_cdp_override(cdp_url: str) -> str:
     For discovery-style endpoints we fetch /json/version and return the
     webSocketDebuggerUrl so downstream tools always receive a concrete browser
     websocket instead of an ambiguous host:port URL.
+    
+    SECURITY FIX (V-010): Validates URLs before fetching to prevent SSRF.
+    Only allows localhost/private network addresses for CDP connections.
     """
     raw = (cdp_url or "").strip()
     if not raw:
@@ -191,6 +194,35 @@ def _resolve_cdp_override(cdp_url: str) -> str:
     else:
         version_url = discovery_url.rstrip("/") + "/json/version"
 
+    # SECURITY FIX (V-010): Validate URL before fetching
+    # Only allow localhost and private networks for CDP
+    from urllib.parse import urlparse
+    parsed = urlparse(version_url)
+    hostname = parsed.hostname or ""
+    
+    # Allow only safe hostnames for CDP
+    allowed_hostnames = ["localhost", "127.0.0.1", "0.0.0.0", "::1"]
+    if hostname not in allowed_hostnames:
+        # Check if it's a private IP
+        try:
+            import ipaddress
+            ip = ipaddress.ip_address(hostname)
+            if not (ip.is_private or ip.is_loopback):
+                logger.error(
+                    "SECURITY: Rejecting CDP URL '%s' - only localhost and private "
+                    "networks are allowed to prevent SSRF attacks.",
+                    raw
+                )
+                return raw  # Return original without fetching
+        except ValueError:
+            # Not an IP - reject unknown hostnames
+            logger.error(
+                "SECURITY: Rejecting CDP URL '%s' - unknown hostname '%s'. "
+                "Only localhost and private IPs are allowed.",
+                raw, hostname
+            )
+            return raw
+
     try:
         response = requests.get(version_url, timeout=10)
         response.raise_for_status()