CVE-2020-8295 in Nextcloud Server
Summary
by MITRE • 01/26/2021
A wrong check in Nextcloud Server 19 and prior allowed to perform a denial of service attack when resetting the password for a user.
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Analysis
by VulDB Data Team • 02/20/2021
The vulnerability identified as CVE-2020-8295 represents a critical flaw in Nextcloud Server versions 19 and earlier that fundamentally undermines the system's security posture through a flawed access control mechanism. This vulnerability specifically affects the password reset functionality, which is a core component of any authentication system. The flaw manifests as an insufficient validation check that fails to properly verify user permissions or account states during the password reset process, creating an exploitable condition that adversaries can leverage for malicious purposes.
The technical implementation of this vulnerability stems from a missing or inadequate authorization check within the password reset workflow. When a user attempts to reset their password, the system should validate that the requester has legitimate authorization to perform this action. However, in affected Nextcloud versions, this validation process contains a logical error that allows unauthorized entities to trigger password reset requests for arbitrary user accounts. This weakness enables attackers to consume system resources and disrupt normal service operations without requiring valid credentials or authentication.
From an operational impact perspective, this vulnerability creates a significant denial of service condition that can severely impact system availability and user experience. Attackers can repeatedly initiate password reset requests for targeted accounts, leading to resource exhaustion and service degradation. The vulnerability can be exploited to create a sustained denial of service attack by continuously flooding the system with reset requests, effectively preventing legitimate users from accessing their accounts or performing normal operations. This attack vector represents a classic example of resource exhaustion that can be amplified through automated tools and scripts.
The vulnerability aligns with CWE-305 authentication weakness categories and represents a failure in proper access control implementation that can be categorized under ATT&CK technique T1486 for data destruction and T1499 for network denial of service. Organizations using affected Nextcloud versions face substantial risk of service disruption and potential account compromise, as the flaw creates opportunities for both denial of service attacks and unauthorized account access. The impact extends beyond simple service interruption to potentially enable broader exploitation attempts that could compromise user data and system integrity.
Mitigation strategies for CVE-2020-8295 require immediate action to upgrade to Nextcloud Server version 20 or later, which contains the necessary fixes to address the flawed validation logic. Organizations should also implement rate limiting mechanisms to prevent excessive password reset requests and monitor system logs for unusual patterns of reset activity. Network-level controls can help detect and block suspicious traffic patterns associated with automated exploitation attempts, while additional monitoring should focus on identifying unauthorized password reset activities that may indicate active exploitation attempts. Security teams should also review and strengthen their incident response procedures to address potential exploitation of this vulnerability effectively.