CVE-2023-23943 : Security Advisory and Response

This CVE involves a Blind SSRF vulnerability via server URL input in the Nextcloud Mail app, impacting certain versions of the Nextcloud home server platform.

Understanding CVE-2023-23943

This vulnerability (CWE-918: Server-Side Request Forgery) allows attackers to initiate requests from the server to other resources, potentially leading to unauthorized actions being performed.

What is CVE-2023-23943?

The Nextcloud Mail app, specifically in affected versions, had fields such as SMTP, IMAP, and Sieve host that allowed scanning for internal services and servers reachable within the local network of the Nextcloud Server.

The Impact of CVE-2023-23943

With a CVSS v3.1 base score of 5 out of 10, this medium severity vulnerability could result in low confidentiality impact and no integrity or availability impact. Attackers with low privileges could exploit this issue to manipulate server requests.

Technical Details of CVE-2023-23943

The following technical details provide more insight into the vulnerability:

Vulnerability Description

The vulnerability in the Nextcloud Mail app allowed for Blind SSRF via server URL input, enabling attackers to interact with internal services and servers accessible within the local network.

Affected Systems and Versions

The affected versions include

>= 2.0.0

and

< 2.2.2

.
Additionally, version

< 1.15.0

is also considered affected.

Exploitation Mechanism

Attackers could exploit this vulnerability by manipulating the server URL input fields in the Nextcloud Mail app to initiate unauthorized requests to internal resources.

Mitigation and Prevention

To address CVE-2023-23943 and enhance security, consider the following mitigation strategies:

Immediate Steps to Take

Upgrade the Nextcloud Mail app to version

1.15.0

or

2.2.2

to mitigate the vulnerability.
Disable the Nextcloud Mail app as a temporary workaround if immediate updating is not feasible.

Long-Term Security Practices

Regularly monitor and update software applications to address security vulnerabilities promptly.
Implement proper input validation and security controls to prevent SSRF attacks and unauthorized server requests.

Patching and Updates

Stay informed about security advisories and patches released by Nextcloud to address vulnerabilities like Blind SSRF via server URL input in the Nextcloud Mail app. Regularly update software to secure against known threats.