CVE-2023-25820 in Server
Summary
by MITRE • 03/22/2023
Nextcloud Server is the file server software for Nextcloud, a self-hosted productivity platform, and Nextcloud Enterprise Server is the enterprise version of the file server software. In Nextcloud Server versions 25.0.x prior to 25.0.5 and versions 24.0.x prior to 24.0.10 as well as Nextcloud Enterprise Server versions 25.0.x prior to 25.0.4, 24.0.x prior to 24.0.10, 23.0.x prior to 23.0.12.5, 22.x prior to 22.2.0.10, and 21.x prior to 21.0.9.10, when an attacker gets access to an already logged in user session they can then brute force the password on the confirmation endpoint. Nextcloud Server should upgraded to 24.0.10 or 25.0.4 and Nextcloud Enterprise Server should upgraded to 21.0.9.10, 22.2.10.10, 23.0.12.5, 24.0.10, or 25.0.4 to receive a patch. No known workarounds are available.
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Analysis
by VulDB Data Team • 04/13/2023
The vulnerability identified as CVE-2023-25820 represents a critical security flaw in Nextcloud Server and Nextcloud Enterprise Server implementations that affects multiple version streams. This issue stems from inadequate session management and authentication confirmation mechanisms that allow attackers with access to an existing user session to perform password brute force attacks against the confirmation endpoint. The vulnerability specifically impacts Nextcloud Server versions 25.0.x before 25.0.5 and 24.0.x before 24.0.10, along with corresponding Enterprise Server versions across multiple release lines including 25.0.x before 25.0.4, 24.0.x before 24.0.10, 23.0.x before 23.0.12.5, 22.x before 22.2.0.10, and 21.x before 21.0.9.10. The flaw creates a significant attack surface where session hijacking can lead to credential compromise through automated password guessing attempts.
The technical implementation of this vulnerability resides in the confirmation endpoint's insufficient validation mechanisms that fail to properly rate-limit or detect brute force attempts when an attacker possesses a valid session token. This weakness allows unauthorized parties to leverage existing authenticated sessions to conduct password brute force operations against the confirmation endpoint, bypassing normal authentication controls that would typically prevent such attacks. The vulnerability aligns with CWE-307 - Improper Restriction of Excessive Authentication Attempts, which specifically addresses the lack of proper rate limiting and detection mechanisms for authentication attempts. From an attack perspective, this vulnerability demonstrates characteristics consistent with ATT&CK technique T1110 - Brute Force, particularly focusing on credential guessing and password spraying attacks that exploit session-based authentication mechanisms.
The operational impact of CVE-2023-25820 extends beyond simple credential theft to potentially enable full system compromise when combined with other attack vectors. An attacker who successfully exploits this vulnerability can gain unauthorized access to user accounts, potentially leading to data exfiltration, privilege escalation, and lateral movement within the network environment. The vulnerability particularly affects organizations that rely on Nextcloud for document management and collaboration, where compromised accounts can result in significant business disruption and regulatory compliance violations. The attack scenario becomes more dangerous when considering that session hijacking can occur through various means including network sniffing, cross-site scripting attacks, or compromised client devices, making this vulnerability particularly concerning for enterprise environments with multiple user endpoints.
Organizations must prioritize immediate remediation through the recommended version upgrades to address this vulnerability effectively. The patched versions include Nextcloud Server 24.0.10 and 25.0.4, with corresponding Enterprise Server patches at 21.0.9.10, 22.2.10.10, 23.0.12.5, 24.0.10, and 25.0.4. These updates contain essential fixes that implement proper rate limiting mechanisms and strengthen the confirmation endpoint's resistance to brute force attacks. Security teams should conduct thorough vulnerability assessments to identify all affected systems and ensure proper patch deployment across all Nextcloud installations. Given the lack of known workarounds, organizations must not delay remediation efforts and should implement additional monitoring controls to detect potential exploitation attempts. The vulnerability demonstrates the importance of maintaining up-to-date security patches and implementing comprehensive session management policies that include proper session invalidation and monitoring for suspicious authentication patterns.