Merge pull request #56 from Zektopic/sentinel/fix-ssrf-bypass-ipv4-mapped-1602020334448431204

🛡️ Sentinel: [CRITICAL] Fix SSRF bypass via IPv4-mapped IPv6 addresses

Author: manupawickramasinghe

.jules/sentinel.md

@@ -36,3 +36,7 @@
 **Vulnerability:** Denial of Service (DoS) via Application Crash.
 **Learning:** Python 3.11+ introduced `sys.set_int_max_str_digits` which limits the conversion between massive integers and strings (e.g., calling `repr()` on an int like `10**100000`). When untrusted large integers are passed as arguments (like `ip` or `timeout`) and later sanitized for logging via `repr()`, it raises an unhandled `ValueError` that bypasses standard exception handlers and crashes the entire worker thread pool.
 **Prevention:** To prevent thread exhaustion and DoS, always explicitly enforce boundary checks (`type(var) is int` and size limits) on arbitrary inputs *before* any string formatting or `repr()` usage. As a defense in depth measure, wrap explicit `repr()` calls on untrusted dynamic inputs in a `try...except ValueError` block to provide a safe fallback string like `<unrepresentable>`.
+## 2024-05-18 - SSRF Bypass via IPv4-mapped IPv6 Addresses
+**Vulnerability:** Attackers could bypass SSRF IP blocklists (e.g., checking `is_link_local` to block 169.254.169.254) by passing the equivalent IPv4-mapped IPv6 address (e.g., `::ffff:169.254.169.254`).
+**Learning:** Python's `ipaddress` module does not apply all IPv4 boolean property checks to IPv4-mapped IPv6 objects. For example, `is_link_local` and `is_unspecified` return `False` for their mapped equivalents, allowing malicious inputs to bypass validation while the OS networking stack natively routes the packet to the IPv4 target.
+**Prevention:** To prevent SSRF bypasses via IPv4-mapped IPv6 addresses, explicitly unwrap the mapped IPv4 address using `getattr(ip_obj, 'ipv4_mapped', None)` and apply security validation checks directly to the underlying `IPv4Address` object if it exists.

test_testping1.py

@@ -53,6 +53,16 @@ def test_is_reachable_type_error(self, mock_call):
                 self.assertIn(f"Invalid IP address format: {repr(invalid_ip)}", log.output[0])
                 mock_call.assert_not_called()
 
+    @patch('testping1.subprocess.call')
+    def test_is_reachable_ssrf_bypass_ipv4_mapped(self, mock_call):
+        """Test is_reachable prevents SSRF bypass via IPv4-mapped IPv6 addresses."""
+        ssrf_mapped_ips = ['::ffff:127.0.0.1', '::ffff:169.254.169.254', '::ffff:224.0.0.1', '::ffff:0.0.0.0', '::ffff:255.255.255.255']
+        for ip in ssrf_mapped_ips:
+            with self.assertLogs(level='ERROR') as log:
+                self.assertFalse(is_reachable(ip))
+                self.assertIn("IP address not allowed for scanning", log.output[0])
+                mock_call.assert_not_called()
+
     @patch('testping1.subprocess.call')
     def test_is_reachable_argument_injection(self, mock_call):
         """Test is_reachable prevents argument injection by rejecting invalid IPs."""

testping1.py

@@ -89,7 +89,17 @@ def is_reachable(ip, timeout=1):
     # 🛡️ Sentinel: Prevent Server-Side Request Forgery (SSRF)
     # Block loopback, link-local, multicast, unspecified, and reserved addresses from being pinged.
     # reserved addresses include the broadcast address (255.255.255.255)
-    if ip_obj.is_loopback or ip_obj.is_link_local or ip_obj.is_multicast or ip_obj.is_unspecified or ip_obj.is_reserved:
+
+    # 🛡️ Sentinel: Prevent SSRF bypass via IPv4-mapped IPv6 addresses.
+    # Python's ipaddress module does not apply all IPv4 property checks (like
+    # is_link_local or is_unspecified) to IPv4-mapped IPv6 addresses (e.g., ::ffff:169.254.169.254).
+    # We must unwrap the IPv4 address before validating it against the blocklist.
+    ip_to_check = ip_obj
+    mapped_ip = getattr(ip_obj, 'ipv4_mapped', None)
+    if mapped_ip is not None:
+        ip_to_check = mapped_ip
+
+    if ip_to_check.is_loopback or ip_to_check.is_link_local or ip_to_check.is_multicast or ip_to_check.is_unspecified or ip_to_check.is_reserved:
         # 🛡️ Sentinel: Sanitize log input using repr() to prevent CRLF/Log Injection
         # IPv6 addresses can contain an arbitrary scope ID (e.g., %eth0\r\n) which is
         # not sanitized by ipaddress.ip_address() and could allow log spoofing.