CVE-2023-39963 in Server
Summary
by MITRE • 08/10/2023
Nextcloud Server provides data storage for Nextcloud, an open source cloud platform. Starting in version 20.0.0 and prior to versions 20.0.14.15, 21.0.9.13, 22.2.10.14, 23.0.12.8, 24.0.12.5, 25.0.9, 26.0.4, and 27.0.1, a missing password confirmation allowed an attacker, after successfully stealing a session from a logged in user, to create app passwords for the victim. Nextcloud server versions 25.0.9, 26.0.4, and 27.0.1 and Nextcloud Enterprise Server versions 20.0.14.15, 21.0.9.13, 22.2.10.14, 23.0.12.9, 24.0.12.5, 25.0.9, 26.0.4, and 27.0.1 contain a patch for this issue. No known workarounds are available.
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Analysis
by VulDB Data Team • 09/05/2023
The vulnerability identified as CVE-2023-39963 represents a critical authorization bypass flaw within Nextcloud Server versions ranging from 20.0.0 through 27.0.0, where the platform failed to enforce proper password confirmation requirements during the creation of application passwords. This security gap stems from a fundamental weakness in the authentication flow that allows attackers to exploit stolen session tokens to generate new app passwords for compromised user accounts without requiring the victim's actual password. The flaw specifically affects the session management and access control mechanisms that govern sensitive administrative operations within the Nextcloud ecosystem, creating a pathway for unauthorized privilege escalation and persistent access to user data.
The technical implementation of this vulnerability manifests through a missing validation check in the application password creation endpoint, which should have required explicit password confirmation before authorizing the generation of new authentication tokens. According to CWE-613, this weakness corresponds to insufficient session validation, where session tokens are accepted without proper verification of the user's current authentication state. The attack vector requires an initial session theft through methods such as cross-site scripting, session hijacking, or man-in-the-middle attacks, followed by exploitation of the password confirmation bypass to create persistent access points. This vulnerability directly aligns with ATT&CK technique T1566.001 for initial access through spearphishing attachments and T1548.002 for privilege escalation through application access tokens.
The operational impact of CVE-2023-39963 extends beyond simple unauthorized access to encompass potential data exfiltration, lateral movement within organizational networks, and persistent backdoor establishment. Once an attacker successfully creates an application password, they gain the ability to access all data and services available to the compromised user account, including files, contacts, calendar entries, and other cloud-stored information. The vulnerability affects all Nextcloud versions prior to the specified patched releases, creating a significant attack surface that spans multiple major versions and enterprise deployments. Organizations using Nextcloud Server without proper patching are at risk of unauthorized data access and potential regulatory compliance violations, particularly in environments where sensitive information is stored.
Organizations should immediately implement the available patches for Nextcloud Server versions 20.0.14.15, 21.0.9.13, 22.2.10.14, 23.0.12.8, 24.0.12.5, 25.0.9, 26.0.4, and 27.0.1 to remediate this vulnerability. System administrators should conduct comprehensive vulnerability assessments to identify potentially compromised sessions and revoke all existing app passwords for affected accounts. Additional security measures include implementing robust session management policies, enabling multi-factor authentication for all user accounts, and deploying network monitoring solutions to detect suspicious authentication patterns. Given the nature of the vulnerability, organizations should also review their incident response procedures to ensure proper handling of session theft and unauthorized access events. The lack of known workarounds means that patching represents the only effective mitigation strategy, making immediate deployment of the security updates critical for maintaining system integrity and protecting user data.