^{CVE-2020-10252:}Server-Side Request Forgery (SSRF) vulnerability in ownCloud before 10.4 allows authenticated attackers to interact with local services or conduct denial of service attacks.

Overview

The vulnerability affects ownCloud server installations before version 10.4. The SSRF vulnerability exists in the external file sharing functionality of ownCloud. When an authenticated user attempts to add an external share, the application does not properly validate the remote URL parameter, allowing attackers to specify internal network addresses. This enables attackers to:

• Probe internal networks and services
• Potentially access internal resources not meant to be accessible
• Cause denial of service by sending numerous requests to internal services
• Bypass network security controls that rely on perimeter defense

This is particularly dangerous in cloud or multi-tenant environments where ownCloud might have access to other internal services within the same network.

Remediation

To address this vulnerability, system administrators should:

1. Update ownCloud to version 10.4 or later, which contains the fix for this vulnerability.
2. If immediate updating is not possible, consider implementing network-level controls to restrict the server's ability to connect to internal services.
3. Monitor for suspicious activities in logs, particularly requests to the file sharing functionality.
4. Consider implementing additional network segmentation to isolate the ownCloud server from sensitive internal services.
5. Review authentication mechanisms to ensure proper access controls are in place.

For developers working with similar systems:

• Always validate and sanitize URL inputs
• Implement allowlists for permitted domains rather than blocklists
• Consider using a dedicated proxy for external requests that can enforce security policies

References

1. ownCloud Security Advisory: https://owncloud.com/security-advisories/ssrf-in-add-to-your-owncloud-functionality/
2. Detailed exploit information: https://blog.hacktivesecurity.com/index.php?controller=post&action=view&id_post=44
3. ownCloud Server Changelog: https://owncloud.org/changelog/server/
4. CWE-918: Server-Side Request Forgery (SSRF): https://cwe.mitre.org/data/definitions/918.html