ApostropheCMS SSRF via Pretty-URL Host Header

Executive Summary

ApostropheCMS, an open-source Node.js content management system, has a vulnerability in versions up to and including 4.30.0 when the 'prettyUrls: true' feature is enabled on '@apostrophecms/file'. This feature builds URLs using the raw 'Host' HTTP request header, which is attacker-controlled. The system then fetches the URL and streams the response back to the requester. Because the 'Host' header can be manipulated by an attacker, an unauthenticated remote attacker can cause the ApostropheCMS process to make outbound HTTP requests to any host accessible on the private network.

The vulnerability is limited by the path component, which is constrained to a specific pattern based on local database lookups, preventing cross-instance data exfiltration. However, it still allows blind Server-Side Request Forgery (SSRF) attacks, enabling attackers to map network topology through response codes, timing differences, and detailed error messages.

As of the publication date, no patched versions addressing this vulnerability are known.

Useful 0 Not Useful 0

Impact Analysis

This vulnerability allows an unauthenticated remote attacker to make the ApostropheCMS server send HTTP requests to arbitrary hosts within the private network. This can be used to perform network reconnaissance by mapping internal network topology through response codes and timing analysis.

Although the impact is somewhat limited because the path is constrained and cross-instance data exfiltration is prevented, the attacker can still gain information about internal network structure and potentially exploit other internal services.

The vulnerability has a CVSS base score of 3.7, indicating a low to medium severity impact, with limited confidentiality impact and no integrity or availability impact.

Useful 0 Not Useful 0

Compliance Impact

The vulnerability allows an unauthenticated remote attacker to make the ApostropheCMS server issue outbound HTTP requests to internal network hosts, potentially enabling network topology mapping and limited data exfiltration across instances.

However, the impact is narrow due to constraints on the requested path and uniqueness of identifiers, which neutralizes cross-instance data exfiltration.

There is no direct information provided about how this vulnerability affects compliance with standards such as GDPR or HIPAA.

Useful 0 Not Useful 0

Detection Guidance

This vulnerability involves the ApostropheCMS server making outbound HTTP requests based on the raw Host header in incoming requests when prettyUrls is enabled. Detection can focus on monitoring outbound HTTP requests from the ApostropheCMS server to unexpected internal or external hosts.

You can check network logs or use network monitoring tools to identify unusual outbound HTTP traffic originating from the ApostropheCMS server.

On the server, you might inspect logs or use commands to monitor outgoing connections, for example:

• Use tcpdump or tshark to capture outbound HTTP traffic: tcpdump -i <interface> 'tcp dst port 80 or tcp dst port 443'
• Use netstat or ss to check active outbound connections: netstat -tnp | grep <apostrophecms_process> or ss -tnp | grep <apostrophecms_process>
• Review web server or application logs for requests with unusual Host headers or unexpected response patterns.

Useful 0 Not Useful 0

Mitigation Strategies

Since no patched versions are available as of the publication date, immediate mitigation involves configuration changes and network controls.

• Disable the prettyUrls feature on @apostrophecms/file if it is enabled, to prevent the vulnerable code path from being triggered.
• Implement network-level restrictions to prevent the ApostropheCMS server from making outbound HTTP requests to unauthorized internal or external hosts.
• Validate and sanitize the Host header in incoming HTTP requests to prevent attacker-controlled values from influencing upstream URL construction.
• Monitor logs and network traffic for suspicious activity indicating exploitation attempts.

Useful 0 Not Useful 0