CVE-2018-16463 in Server
Summary
by MITRE
A bug causing session fixation in Nextcloud Server prior to 14.0.0, 13.0.3 and 12.0.8 could potentially allow an attacker to obtain access to password protected shares.
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Analysis
by VulDB Data Team • 04/07/2020
The vulnerability identified as CVE-2018-16463 represents a critical session fixation flaw within Nextcloud Server versions prior to 14.0.0, 13.0.3, and 12.0.8. This issue stems from inadequate session management practices that fail to properly invalidate or regenerate session identifiers upon user authentication, creating a persistent security weakness that directly impacts the integrity of user access controls. The flaw specifically affects the sharing functionality of Nextcloud, where authenticated users can potentially maintain access to password-protected shares even after legitimate session termination or password changes.
The technical implementation of this vulnerability resides in the session handling mechanism that does not adequately address the session fixation attack vector as defined by CWE-384. When users access password-protected shares within Nextcloud, the system should generate fresh session identifiers upon successful authentication to prevent attackers from exploiting previously established session tokens. However, the vulnerable implementation maintains session identifiers across authentication boundaries, allowing an attacker who has obtained a valid session token to reuse it to gain unauthorized access to shared resources. This flaw particularly affects the authentication flow where users navigate to shared resources that require password verification, creating a window of opportunity for session hijacking attacks.
The operational impact of CVE-2018-16463 extends beyond simple unauthorized access to shared files, as it provides attackers with persistent access rights that can be leveraged for data exfiltration, modification of shared content, or establishment of footholds within organizational networks. The vulnerability creates a scenario where an attacker who successfully captures a session token from a legitimate user can maintain access to password-protected shares even after the original user has logged out or changed their password. This persistent access capability significantly amplifies the potential damage, as it allows attackers to access sensitive data without requiring continuous authentication attempts or complex credential harvesting techniques.
Organizations utilizing vulnerable Nextcloud versions face substantial risk exposure given that the flaw affects core sharing functionality that many enterprises depend upon for collaborative file management. The attack surface expands beyond individual user accounts to include all password-protected shares within the system, potentially exposing confidential documents, business-critical data, or personally identifiable information. Security practitioners should consider this vulnerability in relation to ATT&CK technique T1563.002 which covers credential access through session hijacking, and T1078 which addresses valid accounts usage. The vulnerability's exploitation requires minimal sophistication, making it particularly dangerous in environments where Nextcloud serves as a primary collaboration platform for sensitive organizational data. Mitigation strategies should focus on immediate patch deployment to versions 14.0.0, 13.0.3, or 12.0.8, along with comprehensive session management review processes and monitoring for unauthorized access patterns in shared resource usage.