Executive Summary

[{'type': 'paragraph', 'content': 'CVE-2026-25511 is a high-severity Server-Side Request Forgery (SSRF) vulnerability in the Group-Office PHP package, specifically in the WOPI service discovery component.'}, {'type': 'paragraph', 'content': 'An authenticated user with System Administrator privileges can supply a malicious URL to the WOPI service, which is used without proper validation. This allows the attacker to make the server send HTTP requests to internal hosts and ports.'}, {'type': 'paragraph', 'content': 'The vulnerability also allows the attacker to exfiltrate the response body of these SSRF requests via the built-in debug system, effectively turning the SSRF into a visible attack.'}, {'type': 'paragraph', 'content': 'Additionally, if the server\'s cURL runtime supports the "file://" protocol, the attacker can read arbitrary files on the server by specifying file URLs, with the file contents retrievable through the debug system.'}] [1]

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Impact Analysis

[{'type': 'paragraph', 'content': 'This vulnerability can have several serious impacts:'}, {'type': 'list_item', 'content': 'Unauthorized internal network access, allowing attackers to reach internal hosts and services that are normally inaccessible.'}, {'type': 'list_item', 'content': 'Disclosure of sensitive information by exfiltrating the full HTTP response bodies from SSRF requests.'}, {'type': 'list_item', 'content': 'Full server-side file reading, enabling attackers to read arbitrary files on the server if the "file://" protocol is supported.'}, {'type': 'list_item', 'content': 'Potential exposure of sensitive internal metadata and configuration data.'}] [1]

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Compliance Impact

I don't know

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Detection Guidance

[{'type': 'paragraph', 'content': 'Detection of this vulnerability involves identifying attempts to exploit the SSRF via the WOPI service discovery URL by an authenticated System Administrator user.'}, {'type': 'paragraph', 'content': 'One method is to monitor for HTTP requests that include the "X-Debug: 1" header targeting the WOPI service endpoints, especially calls to community/dev/Debugger/get or WopiService/set.'}, {'type': 'paragraph', 'content': 'Since the exploit involves sending a malicious URL to the WOPI service with appended "/hosting/discovery" or bypassing it with URL fragments, network logs or application logs can be searched for such patterns.'}, {'type': 'paragraph', 'content': 'Suggested commands to detect exploitation attempts include:'}, {'type': 'list_item', 'content': 'Using grep on web server logs to find requests with the "X-Debug: 1" header: grep -i \'X-Debug: 1\' /var/log/nginx/access.log'}, {'type': 'list_item', 'content': 'Searching for URLs containing "/hosting/discovery" or suspicious URL fragments in logs: grep -E \'/hosting/discovery|#\' /var/log/nginx/access.log'}, {'type': 'list_item', 'content': 'Monitoring authenticated System Administrator API calls to WopiService/set or community/dev/Debugger/get endpoints.'}, {'type': 'paragraph', 'content': 'Additionally, reviewing application debug logs for unexpected output of HTTP response bodies from internal requests may indicate exploitation.'}] [1]

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Mitigation Strategies

[{'type': 'paragraph', 'content': 'The primary mitigation step is to upgrade Group-Office to a patched version where this vulnerability is fixed.'}, {'type': 'list_item', 'content': 'Upgrade to Group-Office versions 6.8.150, 25.0.82, or 26.0.5 or later, which contain the fix for CVE-2026-25511.'}, {'type': 'paragraph', 'content': 'If immediate upgrade is not possible, restrict access to the WOPI service discovery URL and debug endpoints to trusted users only, especially limiting System Administrator privileges.'}, {'type': 'paragraph', 'content': 'Disable or restrict the debug system that exposes SSRF response bodies, for example by preventing requests with the "X-Debug: 1" header or disabling debug output in production environments.'}, {'type': 'paragraph', 'content': 'Monitor and audit logs for suspicious SSRF activity and unauthorized internal network access attempts.'}] [1, 2]

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