🛡️ Sentinel: Fix SSRF via DNS resolution & link-local checks #80

google-labs-jules · 2026-01-07T10:49:16Z

Enhanced SSRF protection by adding DNS resolution and link-local IP checks to URL validation.

PR created automatically by Jules for task 2097701723962855090 started by @abhimehro

…nk-local) Description: - **Vulnerability:** The application previously only validated the hostname string of folder URLs. This allowed attackers to bypass SSRF protections by using domains that resolve to internal or private IP addresses (e.g., `localtest.me` -> `127.0.0.1`). Additionally, link-local addresses (used for cloud metadata services) were not explicitly blocked. - **Fix:** Enhanced `validate_folder_url` to: 1. Resolve domains to IP addresses using `socket.getaddrinfo`. 2. Check both IP literals and resolved IPs against `is_private`, `is_loopback`, and `is_link_local` checks. 3. Fail closed on DNS resolution errors. - **Verification:** Added `tests/test_security.py` with test cases for local, private, link-local, and public IPs, as well as DNS failures.

google-labs-jules · 2026-01-07T10:49:18Z

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…5090

main.py

-            if ip.is_private or ip.is_loopback:
-                log.warning(f"Skipping unsafe URL (private IP): {sanitize_for_log(url)}")
+            if ip.is_private or ip.is_loopback or ip.is_link_local:
+                log.warning(f"Skipping unsafe URL (private/unsafe IP): {sanitize_for_log(url)}")


main.py

+                    ip = ipaddress.ip_address(ip_str)
+                    # Block private, loopback, AND link-local (e.g. 169.254.x.x for cloud metadata)
+                    if ip.is_private or ip.is_loopback or ip.is_link_local:
+                        log.warning(f"Skipping unsafe URL (domain {hostname} resolves to unsafe IP {ip_str}): {sanitize_for_log(url)}")


main.py

+                        log.warning(f"Skipping unsafe URL (domain {hostname} resolves to unsafe IP {ip_str}): {sanitize_for_log(url)}")
+                        return False
+            except socket.gaierror:
+                log.warning(f"Skipping URL (DNS resolution failed): {sanitize_for_log(url)}")


main.py

+                log.warning(f"Skipping URL (DNS resolution failed): {sanitize_for_log(url)}")
+                return False
+            except Exception as e:
+                log.warning(f"Error resolving domain {sanitize_for_log(hostname)}: {e}")


tests/test_security.py

+import unittest
+from unittest.mock import patch
+import socket
+import ipaddress


tests/test_security.py

+
+        self.assertFalse(is_valid, "Should reject URL if DNS resolution fails")
+
+if __name__ == '__main__':


main.py

+                # We use getaddrinfo to support both IPv4 and IPv6
+                for _, _, _, _, sockaddr in socket.getaddrinfo(hostname, None):
+                    ip_str = sockaddr[0]
+                    ip = ipaddress.ip_address(ip_str)


main.py

+                    ip = ipaddress.ip_address(ip_str)
+                    # Block private, loopback, AND link-local (e.g. 169.254.x.x for cloud metadata)
+                    if ip.is_private or ip.is_loopback or ip.is_link_local:
+                        log.warning(f"Skipping unsafe URL (domain {hostname} resolves to unsafe IP {ip_str}): {sanitize_for_log(url)}")


tests/test_security.py

@@ -0,0 +1,86 @@
+import unittest


tests/test_security.py

+# Note: This will execute the top-level code in main.py.
+import main
+
+class TestSSRFProtection(unittest.TestCase):


tests/test_security.py

+class TestSSRFProtection(unittest.TestCase):
+
+    @patch('socket.getaddrinfo')
+    def test_domain_resolving_to_localhost(self, mock_getaddrinfo):


tests/test_security.py

+        self.assertFalse(is_valid, "Should reject link-local IP literal")
+
+    @patch('socket.getaddrinfo')
+    def test_domain_resolving_to_link_local(self, mock_getaddrinfo):


tests/test_security.py

+        self.assertFalse(is_valid, "Should reject domain resolving to link-local IP")
+
+    @patch('socket.getaddrinfo')
+    def test_domain_resolving_to_public_ip(self, mock_getaddrinfo):


tests/test_security.py

+        self.assertTrue(is_valid, "Should accept domain resolving to public IP")
+
+    @patch('socket.getaddrinfo')
+    def test_dns_resolution_failure(self, mock_getaddrinfo):


main.py

-            pass
+            # Not an IP literal, it's a domain. Resolve it.
+            try:
+                # Resolve hostname to check if it points to a private IP


tests/test_security.py

+import unittest
+from unittest.mock import patch
+import socket
+import ipaddress


tests/test_security.py

+        self.assertTrue(is_valid, "Should accept domain resolving to public IP")
+
+    @patch('socket.getaddrinfo')
+    def test_dns_resolution_failure(self, mock_getaddrinfo):


tests/test_security.py

+        self.assertFalse(is_valid, "Should reject domain resolving to link-local IP")
+
+    @patch('socket.getaddrinfo')
+    def test_domain_resolving_to_public_ip(self, mock_getaddrinfo):


tests/test_security.py

+        self.assertFalse(is_valid, "Should reject link-local IP literal")
+
+    @patch('socket.getaddrinfo')
+    def test_domain_resolving_to_link_local(self, mock_getaddrinfo):


tests/test_security.py

+
+        self.assertFalse(is_valid, "Should reject domain resolving to private IP")
+
+    def test_ip_literal_link_local(self):


tests/test_security.py

+        self.assertFalse(is_valid, "Should reject domain resolving to localhost")
+
+    @patch('socket.getaddrinfo')
+    def test_domain_resolving_to_private_ip(self, mock_getaddrinfo):


tests/test_security.py

+import unittest
+from unittest.mock import patch
+import socket
+import ipaddress


main.py

+                log.warning(f"Skipping URL (DNS resolution failed): {sanitize_for_log(url)}")
+                return False
+            except Exception as e:
+                log.warning(f"Error resolving domain {sanitize_for_log(hostname)}: {e}")


main.py

+                        log.warning(f"Skipping unsafe URL (domain {hostname} resolves to unsafe IP {ip_str}): {sanitize_for_log(url)}")
+                        return False
+            except socket.gaierror:
+                log.warning(f"Skipping URL (DNS resolution failed): {sanitize_for_log(url)}")


main.py

+                    ip = ipaddress.ip_address(ip_str)
+                    # Block private, loopback, AND link-local (e.g. 169.254.x.x for cloud metadata)
+                    if ip.is_private or ip.is_loopback or ip.is_link_local:
+                        log.warning(f"Skipping unsafe URL (domain {hostname} resolves to unsafe IP {ip_str}): {sanitize_for_log(url)}")


main.py

-            if ip.is_private or ip.is_loopback:
-                log.warning(f"Skipping unsafe URL (private IP): {sanitize_for_log(url)}")
+            if ip.is_private or ip.is_loopback or ip.is_link_local:
+                log.warning(f"Skipping unsafe URL (private/unsafe IP): {sanitize_for_log(url)}")


Copilot

Pull request overview

This PR enhances SSRF (Server-Side Request Forgery) protection by adding DNS resolution checks and blocking link-local IP addresses in URL validation. The changes prevent attackers from bypassing security checks using domains that resolve to private/internal IPs or using link-local addresses like 169.254.169.254 (AWS metadata endpoint).

Key changes:

Added DNS resolution to validate_folder_url to check resolved IPs, not just hostname strings
Extended IP blocking to include link-local addresses (169.254.0.0/16) via is_link_local check
Added comprehensive test suite for the new SSRF protections

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 6 comments.

File	Description
main.py	Enhanced validate_folder_url with DNS resolution logic and link-local IP blocking
tests/test_security.py	Added comprehensive unit tests for SSRF protection scenarios including DNS resolution cases
.jules/sentinel.md	Documented the security vulnerability, learnings, and prevention measures

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Copilot · 2026-01-09T00:18:22Z

tests/test_security.py

+
+class TestSSRFProtection(unittest.TestCase):
+
+    @patch('socket.getaddrinfo')


The mock decorator is patching 'socket.getaddrinfo' globally, but it should patch 'main.socket.getaddrinfo' instead. Since main.py imports socket and calls socket.getaddrinfo, the patch needs to target where it's used (in the main module) rather than the socket module itself. This applies to all test methods that use @patch('socket.getaddrinfo').

Copilot · 2026-01-09T00:18:23Z

tests/test_security.py

+
+        self.assertFalse(is_valid, "Should reject domain resolving to localhost")
+
+    @patch('socket.getaddrinfo')


The mock decorator is patching 'socket.getaddrinfo' globally, but it should patch 'main.socket.getaddrinfo' instead. Since main.py imports socket and calls socket.getaddrinfo, the patch needs to target where it's used (in the main module) rather than the socket module itself.

Copilot · 2026-01-09T00:18:23Z

tests/test_security.py

+        is_valid = main.validate_folder_url(url)
+        self.assertFalse(is_valid, "Should reject link-local IP literal")
+
+    @patch('socket.getaddrinfo')


The mock decorator is patching 'socket.getaddrinfo' globally, but it should patch 'main.socket.getaddrinfo' instead. Since main.py imports socket and calls socket.getaddrinfo, the patch needs to target where it's used (in the main module) rather than the socket module itself.

Copilot · 2026-01-09T00:18:23Z

tests/test_security.py

+
+        self.assertFalse(is_valid, "Should reject domain resolving to link-local IP")
+
+    @patch('socket.getaddrinfo')


The mock decorator is patching 'socket.getaddrinfo' globally, but it should patch 'main.socket.getaddrinfo' instead. Since main.py imports socket and calls socket.getaddrinfo, the patch needs to target where it's used (in the main module) rather than the socket module itself.

Copilot · 2026-01-09T00:18:23Z

tests/test_security.py

+
+        self.assertTrue(is_valid, "Should accept domain resolving to public IP")
+
+    @patch('socket.getaddrinfo')


The mock decorator is patching 'socket.getaddrinfo' globally, but it should patch 'main.socket.getaddrinfo' instead. Since main.py imports socket and calls socket.getaddrinfo, the patch needs to target where it's used (in the main module) rather than the socket module itself.

Copilot · 2026-01-09T00:18:24Z

tests/test_security.py

+import unittest
+from unittest.mock import patch
+import socket
+import ipaddress


Import of 'ipaddress' is not used.

Suggested change

import ipaddress

Merge branch 'main' into sentinel/fix-ssrf-validation-209770172396285…

a464d05

…5090

abhimehro marked this pull request as ready for review January 9, 2026 00:13

Copilot AI review requested due to automatic review settings January 9, 2026 00:13

abhimehro assigned abhimehro and Copilot Jan 9, 2026

github-actions bot added the python label Jan 9, 2026

Copilot started reviewing on behalf of abhimehro January 9, 2026 00:14 View session

github-advanced-security bot found potential problems Jan 9, 2026

View reviewed changes

Copilot AI reviewed Jan 9, 2026

View reviewed changes


		self.assertFalse(is_valid, "Should reject URL if DNS resolution fails")

		if __name__ == '__main__':


		self.assertFalse(is_valid, "Should reject domain resolving to private IP")

		def test_ip_literal_link_local(self):


		class TestSSRFProtection(unittest.TestCase):

		@patch('socket.getaddrinfo')


		self.assertTrue(is_valid, "Should accept domain resolving to public IP")

		@patch('socket.getaddrinfo')

🛡️ Sentinel: Fix SSRF via DNS resolution & link-local checks #80

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🛡️ Sentinel: Fix SSRF via DNS resolution & link-local checks #80

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