CVE-2017-5865 in ownCloud Server
Summary
by MITRE
The password reset functionality in ownCloud Server before 8.1.11, 8.2.x before 8.2.9, 9.0.x before 9.0.7, and 9.1.x before 9.1.3 sends different error messages depending on whether the username is valid, which allows remote attackers to enumerate user names via a large number of password reset attempts.
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Analysis
by VulDB Data Team • 09/04/2020
The vulnerability identified as CVE-2017-5865 affects ownCloud Server versions prior to specific patch releases, exposing a critical flaw in the password reset mechanism that enables unauthorized user enumeration. This weakness stems from the application's inconsistent error messaging behavior during password reset requests, where the system provides different responses based on whether the targeted username exists within the system. The vulnerability represents a classic information disclosure issue that directly violates security principles by inadvertently revealing system state information to unauthorized parties.
The technical implementation of this vulnerability occurs within the password reset functionality of ownCloud's authentication system. When a user attempts to reset a password, the server checks if the provided username exists in the user database and responds with distinct error messages accordingly. Valid usernames trigger one type of response while invalid usernames generate another, creating a predictable pattern that attackers can exploit through automated means. This design flaw allows adversaries to systematically test usernames by observing the server's response variations, effectively bypassing traditional account enumeration protection mechanisms.
From an operational impact perspective, this vulnerability creates significant risk for organizations relying on ownCloud for file sharing and collaboration services. Attackers can leverage this weakness to compile comprehensive lists of valid user accounts, which serves as a foundation for subsequent attacks including brute force password guessing, credential stuffing campaigns, or social engineering operations. The vulnerability's exploitation requires minimal technical skill and can be automated, making it particularly dangerous in environments where user enumeration could lead to privilege escalation or unauthorized access to sensitive data repositories. The issue directly aligns with CWE-200, which addresses information exposure through improper error handling, and represents a clear violation of the principle of least privilege.
The attack vector for this vulnerability follows standard reconnaissance patterns where threat actors initiate multiple password reset requests targeting various username combinations. By analyzing response times and error messages, attackers can distinguish between valid and invalid accounts, gradually building a complete user directory for the targeted system. This enumeration capability significantly reduces the attack surface for subsequent exploitation attempts and demonstrates how seemingly minor implementation flaws can create substantial security risks. Organizations using affected versions of ownCloud should immediately implement mitigations including implementing account lockout mechanisms, rate limiting for password reset requests, and ensuring consistent error messaging regardless of account validity. The vulnerability also highlights the importance of following secure coding practices as outlined in the OWASP Top Ten and aligns with ATT&CK technique T1078 for valid accounts and T1566 for credential harvesting, emphasizing the need for comprehensive security controls beyond basic authentication mechanisms.