Attack Chain

1. Attacker identifies a vulnerable Nextcloud instance.
2. Attacker exploits a vulnerability to bypass authentication mechanisms.
3. Attacker leverages information disclosure vulnerability to gather sensitive information about the system and users.
4. Attacker crafts a SQL injection payload.
5. Attacker injects the malicious SQL payload into a vulnerable input field.
6. The SQL injection allows the attacker to read sensitive data from the database, such as user credentials.
7. Attacker uses stolen credentials to escalate privileges within the Nextcloud instance.
8. Attacker gains unauthorized access to sensitive data and functionalities, potentially exfiltrating data or disrupting services.

Impact

Successful exploitation of these vulnerabilities could lead to unauthorized access to sensitive data, including user credentials and confidential files. The SQL injection vulnerability could allow an attacker to gain complete control over the Nextcloud instance, potentially leading to data breaches, service disruption, and reputational damage. The number of affected users depends on the scale of the Nextcloud deployment.

Recommendation

• Deploy the Sigma rules in this brief to your SIEM and tune for your environment to detect potential exploitation attempts.
• Review web server logs for suspicious activity and SQL injection attempts, enabling you to detect and respond to potential attacks (log source: webserver).
• Ensure Nextcloud instances are updated to the latest patched version to remediate the vulnerabilities (affected_products: Nextcloud).