CVE-2020-8138 : Security Advisory and Response

A missing check for IPv4 nested inside IPv6 in Nextcloud server < 17.0.1, < 16.0.7, and < 15.0.14 allowed a Server-Side Request Forgery (SSRF) vulnerability when subscribing to a malicious calendar URL.

Understanding CVE-2020-8138

This CVE involves a Server-Side Request Forgery (SSRF) vulnerability in Nextcloud Server versions prior to 17.0.1, 16.0.7, and 15.0.14.

What is CVE-2020-8138?

CVE-2020-8138 is a security vulnerability in Nextcloud Server that could be exploited by an attacker to perform Server-Side Request Forgery (SSRF) attacks.

The Impact of CVE-2020-8138

The vulnerability could allow an attacker to trigger SSRF attacks by subscribing to a malicious calendar URL, potentially leading to unauthorized access to internal systems or services.

Technical Details of CVE-2020-8138

This section provides more technical insights into the vulnerability.

Vulnerability Description

The missing check for IPv4 nested inside IPv6 in affected Nextcloud Server versions created an SSRF vulnerability, enabling attackers to manipulate server requests.

Affected Systems and Versions

Product: Nextcloud Server
Versions Affected: < 17.0.1, < 16.0.7, < 15.0.14
Fixed Versions: 17.0.2, 16.0.7, 15.0.14

Exploitation Mechanism

Attackers could exploit this vulnerability by tricking the server into making requests to unintended destinations through a crafted calendar URL.

Mitigation and Prevention

Protecting systems from CVE-2020-8138 requires immediate actions and long-term security practices.

Immediate Steps to Take

Update Nextcloud Server to the fixed versions: 17.0.2, 16.0.7, or 15.0.14.
Monitor and restrict outgoing server requests to prevent SSRF attacks.

Long-Term Security Practices

Implement input validation to prevent malicious input manipulation.
Regularly audit and review server configurations for security vulnerabilities.

Patching and Updates

Stay informed about security advisories from Nextcloud and apply patches promptly to address known vulnerabilities.