🛡️ Sentinel: Fix SSRF via DNS resolution in URL validation by google-labs-jules[bot] · Pull Request #72 · abhimehro/ctrld-sync

google-labs-jules · 2026-01-05T10:35:47Z

Implemented DNS resolution check in validate_folder_url to prevent SSRF via domain names resolving to private IPs.

PR created automatically by Jules for task 5407761294063338854 started by @abhimehro

Modified `validate_folder_url` in `main.py` to resolve domain names using `socket.getaddrinfo`. This prevents SSRF attacks where a malicious domain resolves to a private IP address (e.g., localhost). The check now verifies that all resolved IPs are not private or loopback addresses before allowing the URL. Fail-closed behavior is implemented for DNS resolution failures. Security Journal updated with this finding.

google-labs-jules · 2026-01-05T10:35:48Z

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…8854

Copilot

Pull request overview

This PR fixes an SSRF vulnerability in URL validation by adding DNS resolution checks to prevent attackers from using domain names that resolve to private IP addresses to bypass security controls.

Key Changes:

Added DNS resolution using socket.getaddrinfo() to validate that domain names don't resolve to private/loopback IPs
Updated exception handling to treat DNS resolution failures as unsafe (fail-closed approach)
Documented the vulnerability and prevention approach in the Sentinel security log

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 4 comments.

File	Description
main.py	Added socket import and DNS resolution logic in `validate_folder_url` to check if domains resolve to private/loopback IPs
.jules/sentinel.md	Documented the SSRF via DNS resolution vulnerability, learning, and prevention measures

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Copilot · 2026-01-09T00:03:38Z

main.py

+                    if resolved_ip.is_private or resolved_ip.is_loopback:
+                        log.warning(f"Skipping unsafe URL (domain {sanitize_for_log(hostname)} resolves to private IP {resolved_ip}): {sanitize_for_log(url)}")
+                        return False
+            except socket.gaierror:


The exception handling only catches socket.gaierror, but socket.getaddrinfo() can also raise other exceptions such as OSError (for network issues) or socket.timeout. While these would be caught by the outer exception handler at line 227, they would result in a generic error message rather than being treated as DNS resolution failures. Consider catching (socket.gaierror, OSError) for more comprehensive error handling.

Suggested change

except socket.gaierror:

except (socket.gaierror, OSError):

Copilot · 2026-01-09T00:03:39Z

main.py

+                for family, kind, proto, canonname, sockaddr in addr_infos:
+                    ip_str = sockaddr[0]
+                    resolved_ip = ipaddress.ip_address(ip_str)
+                    if resolved_ip.is_private or resolved_ip.is_loopback:


The security check is incomplete. In addition to is_private and is_loopback, you should also check for other dangerous IP ranges:

is_link_local: Covers IPv6 link-local addresses (fe80::/10) and IPv4 link-local (169.254.0.0/16)

is_reserved: Includes reserved IP ranges that shouldn't be accessed

is_multicast: Multicast addresses could potentially be abused

Consider updating the condition to: if resolved_ip.is_private or resolved_ip.is_loopback or resolved_ip.is_link_local or resolved_ip.is_reserved or resolved_ip.is_multicast:

Copilot · 2026-01-09T00:03:39Z

main.py

+            try:
+                # Resolve hostname to IPs
+                addr_infos = socket.getaddrinfo(hostname, None)
+                for family, kind, proto, canonname, sockaddr in addr_infos:
+                    ip_str = sockaddr[0]
+                    resolved_ip = ipaddress.ip_address(ip_str)
+                    if resolved_ip.is_private or resolved_ip.is_loopback:
+                        log.warning(f"Skipping unsafe URL (domain {sanitize_for_log(hostname)} resolves to private IP {resolved_ip}): {sanitize_for_log(url)}")
+                        return False


This implementation has a Time-Of-Check-Time-Of-Use (TOCTOU) vulnerability. DNS resolution happens during validation, but the actual HTTP request occurs later. An attacker could exploit DNS rebinding by having their DNS server return a safe IP during validation and then a private IP when the actual request is made moments later. While this is a known limitation of DNS-based SSRF protection, consider documenting this limitation and potentially adding a note about DNS caching or re-validation closer to the actual request time if feasible.

Copilot · 2026-01-09T00:03:39Z

main.py

+                addr_infos = socket.getaddrinfo(hostname, None)
+                for family, kind, proto, canonname, sockaddr in addr_infos:
+                    ip_str = sockaddr[0]
+                    resolved_ip = ipaddress.ip_address(ip_str)


For IPv6 addresses with zone IDs (e.g., fe80::1%eth0), the sockaddr[0] extraction might include the zone identifier, which could cause ipaddress.ip_address() to raise a ValueError. While this would be caught by the outer exception handler, it would result in an unclear error message. Consider stripping the zone identifier if present by using ip_str.split('%')[0] before passing to ipaddress.ip_address().

Suggested change

resolved_ip = ipaddress.ip_address(ip_str)

# Strip IPv6 zone identifier (e.g., "%eth0") if present

ip_no_zone = ip_str.split('%', 1)[0]

resolved_ip = ipaddress.ip_address(ip_no_zone)

…8854

abhimehro · 2026-01-09T00:10:10Z

Hi @copilot, please open a new pull request to apply changes based on the comments in this thread. Thank you!

Copilot · 2026-01-09T00:10:19Z

@abhimehro I've opened a new pull request, #85, to work on those changes. Once the pull request is ready, I'll request review from you.

main.py

+            try:
+                # Resolve hostname to IPs
+                addr_infos = socket.getaddrinfo(hostname, None)
+                for family, kind, proto, canonname, sockaddr in addr_infos:


main.py

+                    ip_str = sockaddr[0]
+                    resolved_ip = ipaddress.ip_address(ip_str)
+                    if resolved_ip.is_private or resolved_ip.is_loopback:
+                        log.warning(f"Skipping unsafe URL (domain {sanitize_for_log(hostname)} resolves to private IP {resolved_ip}): {sanitize_for_log(url)}")


main.py

+                        log.warning(f"Skipping unsafe URL (domain {sanitize_for_log(hostname)} resolves to private IP {resolved_ip}): {sanitize_for_log(url)}")
+                        return False
+            except socket.gaierror:
+                log.warning(f"Could not resolve hostname {sanitize_for_log(hostname)}, treating as unsafe.")


.jules/sentinel.md

 1. Parse URLs and check hostnames against `localhost` and private IP ranges using `ipaddress` module.
 2. Enforce strict length limits on user inputs (e.g., profile IDs) to prevent resource exhaustion or buffer abuse.
+
+## 2025-01-24 - [SSRF via DNS Resolution]


.jules/sentinel.md

 1. Parse URLs and check hostnames against `localhost` and private IP ranges using `ipaddress` module.
 2. Enforce strict length limits on user inputs (e.g., profile IDs) to prevent resource exhaustion or buffer abuse.
+
+## 2025-01-24 - [SSRF via DNS Resolution]


main.py

+                    ip_str = sockaddr[0]
+                    resolved_ip = ipaddress.ip_address(ip_str)
+                    if resolved_ip.is_private or resolved_ip.is_loopback:
+                        log.warning(f"Skipping unsafe URL (domain {sanitize_for_log(hostname)} resolves to private IP {resolved_ip}): {sanitize_for_log(url)}")


main.py

+                        log.warning(f"Skipping unsafe URL (domain {sanitize_for_log(hostname)} resolves to private IP {resolved_ip}): {sanitize_for_log(url)}")
+                        return False
+            except socket.gaierror:
+                log.warning(f"Could not resolve hostname {sanitize_for_log(hostname)}, treating as unsafe.")


main.py

+            try:
+                # Resolve hostname to IPs
+                addr_infos = socket.getaddrinfo(hostname, None)
+                for family, kind, proto, canonname, sockaddr in addr_infos:


main.py

+            try:
+                # Resolve hostname to IPs
+                addr_infos = socket.getaddrinfo(hostname, None)
+                for family, kind, proto, canonname, sockaddr in addr_infos:


main.py

+            try:
+                # Resolve hostname to IPs
+                addr_infos = socket.getaddrinfo(hostname, None)
+                for family, kind, proto, canonname, sockaddr in addr_infos:


main.py

+            try:
+                # Resolve hostname to IPs
+                addr_infos = socket.getaddrinfo(hostname, None)
+                for family, kind, proto, canonname, sockaddr in addr_infos:


main.py

+                    ip_str = sockaddr[0]
+                    resolved_ip = ipaddress.ip_address(ip_str)
+                    if resolved_ip.is_private or resolved_ip.is_loopback:
+                        log.warning(f"Skipping unsafe URL (domain {sanitize_for_log(hostname)} resolves to private IP {resolved_ip}): {sanitize_for_log(url)}")


main.py

+                        log.warning(f"Skipping unsafe URL (domain {sanitize_for_log(hostname)} resolves to private IP {resolved_ip}): {sanitize_for_log(url)}")
+                        return False
+            except socket.gaierror:
+                log.warning(f"Could not resolve hostname {sanitize_for_log(hostname)}, treating as unsafe.")


main.py

+            try:
+                # Resolve hostname to IPs
+                addr_infos = socket.getaddrinfo(hostname, None)
+                for family, kind, proto, canonname, sockaddr in addr_infos:


main.py

+            try:
+                # Resolve hostname to IPs
+                addr_infos = socket.getaddrinfo(hostname, None)
+                for family, kind, proto, canonname, sockaddr in addr_infos:


main.py

+            try:
+                # Resolve hostname to IPs
+                addr_infos = socket.getaddrinfo(hostname, None)
+                for family, kind, proto, canonname, sockaddr in addr_infos:


main.py

+            try:
+                # Resolve hostname to IPs
+                addr_infos = socket.getaddrinfo(hostname, None)
+                for family, kind, proto, canonname, sockaddr in addr_infos:


main.py

+                    ip_str = sockaddr[0]
+                    resolved_ip = ipaddress.ip_address(ip_str)
+                    if resolved_ip.is_private or resolved_ip.is_loopback:
+                        log.warning(f"Skipping unsafe URL (domain {sanitize_for_log(hostname)} resolves to private IP {resolved_ip}): {sanitize_for_log(url)}")


main.py

+                        log.warning(f"Skipping unsafe URL (domain {sanitize_for_log(hostname)} resolves to private IP {resolved_ip}): {sanitize_for_log(url)}")
+                        return False
+            except socket.gaierror:
+                log.warning(f"Could not resolve hostname {sanitize_for_log(hostname)}, treating as unsafe.")


google-labs-jules · 2026-01-09T00:13:46Z

Hi @copilot, please open a new pull request to apply changes based on the comments in this thread. Thank you!

I have implemented the requested changes from the review thread:

Added comprehensive IP checks (link-local, reserved, multicast).
Added OSError to the exception handling for DNS resolution.
Implemented IPv6 zone identifier stripping.
Added a comment acknowledging the TOCTOU limitation.

Modified `validate_folder_url` in `main.py` to resolve domain names using `socket.getaddrinfo`. This prevents SSRF attacks where a malicious domain resolves to a private or restricted IP address. Key changes: - Added `socket` import and DNS resolution logic. - Validates resolved IPs against private, loopback, link-local, reserved, and multicast ranges. - Implemented secure fail-closed behavior for DNS resolution errors (`socket.gaierror`, `OSError`). - Added handling for IPv6 zone identifiers. - Added code comment acknowledging TOCTOU limitations (DNS rebinding). - Updated security journal.

- Enhanced exception handling to catch OSError in addition to socket.gaierror - Added comprehensive IP range checks (link_local, reserved, multicast) - Strip IPv6 zone identifiers before validation - Document TOCTOU vulnerability limitation in code comments and sentinel.md Co-authored-by: abhimehro <84992105+abhimehro@users.noreply.github.com>

Co-authored-by: abhimehro <84992105+abhimehro@users.noreply.github.com>

…copilot/sub-pr-72

Copilot

Pull request overview

Copilot reviewed 11 out of 11 changed files in this pull request and generated 4 comments.

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.github/workflows/sync.yml

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Copilot · 2026-01-09T00:22:16Z

main.py

+                addr_infos = socket.getaddrinfo(hostname, None)
+                for family, kind, proto, canonname, sockaddr in addr_infos:
+                    ip_str = sockaddr[0]
+
+                    # Strip IPv6 zone identifier if present (e.g., fe80::1%eth0)
+                    if '%' in ip_str:
+                        ip_str = ip_str.split('%', 1)[0]
+
+                    resolved_ip = ipaddress.ip_address(ip_str)
+
+                    if (resolved_ip.is_private or
+                        resolved_ip.is_loopback or
+                        resolved_ip.is_link_local or
+                        resolved_ip.is_reserved or
+                        resolved_ip.is_multicast):
+                        log.warning(f"Skipping unsafe URL (domain {sanitize_for_log(hostname)} resolves to restricted IP {resolved_ip}): {sanitize_for_log(url)}")
+                        return False


If socket.getaddrinfo returns an empty list (which is theoretically possible in edge cases), the loop will not execute and the function will proceed to return True at line 243, allowing the potentially unsafe URL. While this scenario is unlikely in practice, consider adding an explicit check after the getaddrinfo call to ensure at least one address was resolved, or track whether any iteration occurred to ensure the validation actually ran.

Copilot · 2026-01-09T00:22:17Z

main.py

+                    if '%' in ip_str:
+                        ip_str = ip_str.split('%', 1)[0]
+
+                    resolved_ip = ipaddress.ip_address(ip_str)


The exception handling for ipaddress.ip_address(ip_str) on line 226 is not explicitly caught. If the resolved IP address string is malformed or invalid, this could raise a ValueError that would be caught by the outer exception handler on line 239, but it would not be logged with a specific message. Consider adding explicit exception handling around the ipaddress.ip_address() call to log parsing errors more clearly, or ensure that any IP string format issues from socket.getaddrinfo are properly handled.

Suggested change

resolved_ip = ipaddress.ip_address(ip_str)

try:

resolved_ip = ipaddress.ip_address(ip_str)

except ValueError as ve:

log.warning(

f"Failed to parse resolved IP {sanitize_for_log(ip_str)} for hostname "

f"{sanitize_for_log(hostname)}: {ve}. Treating URL as unsafe."

)

return False

Enhance SSRF DNS validation with comprehensive IP checks and IPv6 support

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

abhimehro · 2026-01-18T21:25:50Z

Superseded: Security improvements already in main.

google-labs-jules · 2026-01-18T21:27:49Z

Superseded: Security improvements already in main.

Understood. Acknowledging that this work is now superseded and stopping work on this task.

abhimehro requested review from abhimehro and Copilot January 8, 2026 23:59

abhimehro assigned abhimehro and Copilot Jan 8, 2026

Merge branch 'main' into sentinel-ssrf-dns-resolution-540776129406333…

71f097d

…8854

abhimehro marked this pull request as ready for review January 8, 2026 23:59

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Merge branch 'main' into sentinel-ssrf-dns-resolution-540776129406333…

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…8854

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Enhance SSRF DNS validation with comprehensive IP checks and IPv6 support #85

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Add comprehensive IP checks to literal IP validation for consistency

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Co-authored-by: abhimehro <84992105+abhimehro@users.noreply.github.com>

github-actions bot added documentation Improvements or additions to documentation configuration labels Jan 9, 2026

Merge branch 'sentinel-ssrf-dns-resolution-5407761294063338854' into …

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Merge pull request #85 from abhimehro/copilot/sub-pr-72

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Enhance SSRF DNS validation with comprehensive IP checks and IPv6 support

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abhimehro closed this Jan 18, 2026

-                    resolved_ip = ipaddress.ip_address(ip_str)
+                    # Strip IPv6 zone identifier (e.g., "%eth0") if present
+                    ip_no_zone = ip_str.split('%', 1)[0]
+                    resolved_ip = ipaddress.ip_address(ip_no_zone)

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