CVE-2021-32703 : Security Advisory and Response

This article provides details about CVE-2021-32703, a vulnerability in Nextcloud Server that allowed enumeration of potentially valid share tokens due to a lack of ratelimiting on the shareinfo endpoint.

Understanding CVE-2021-32703

CVE-2021-32703 is a vulnerability in Nextcloud Server versions prior to 19.0.13, 20.0.11, and 21.0.3 that could have enabled attackers to exploit the lack of ratelimiting on the shareinfo endpoint to extract share tokens.

What is CVE-2021-32703?

Nextcloud Server's versions before specified updates had a security flaw wherein attackers could potentially access valid share tokens by exploiting the lack of proper rate limiting on the shareinfo endpoint.

The Impact of CVE-2021-32703

The medium-severity vulnerability with a CVSS base score of 5.3 posed a risk of unauthorized access to sensitive information stored on Nextcloud Server instances, affecting confidentiality and integrity.

Technical Details of CVE-2021-32703

The vulnerability lacked rate limiting on the shareinfo endpoint, potentially enabling attackers to extract share tokens.

Vulnerability Description

Inadequate rate limiting on the shareinfo endpoint in affected Nextcloud Server versions allowed attackers to enumerate valid share tokens, compromising data security.

Affected Systems and Versions

Nextcloud Server versions prior to 19.0.13, 20.0.11, and 21.0.3 were vulnerable to this security issue.

Exploitation Mechanism

Attackers could exploit the lack of rate limiting on the shareinfo endpoint to enumerate potentially valid share tokens, leading to unauthorized data access.

Mitigation and Prevention

Addressing CVE-2021-32703 requires immediate action to secure Nextcloud Server instances and implementing long-term security practices.

Immediate Steps to Take

Users should update Nextcloud Server to versions 19.0.13, 20.0.11, or 21.0.3 to mitigate the vulnerability and prevent exploitation.

Long-Term Security Practices

Regularly updating Nextcloud Server and implementing proper security configurations help in safeguarding against similar vulnerabilities in the future.

Patching and Updates

Installing the patched versions 19.0.13, 20.0.11, or 21.0.3 is crucial to addressing the lack of ratelimit on the shareinfo endpoint vulnerability.