CVE-2023-47102 in Server
Summary
by MITRE • 11/07/2023
UrBackup Server 2.5.31 allows brute-force enumeration of user accounts because a failure message confirms that a username is not valid.
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Analysis
by VulDB Data Team • 02/21/2026
The vulnerability identified as CVE-2023-47102 affects UrBackup Server version 2.5.31 and represents a critical security flaw that undermines the system's authentication mechanism through improper error handling. This issue stems from the server's response behavior during user authentication attempts where it provides distinct feedback for valid and invalid usernames, creating a predictable pattern that adversaries can exploit for account enumeration attacks. The flaw directly impacts the server's ability to maintain secure access controls by exposing user account information through seemingly innocuous error messages that confirm whether a given username exists within the system.
The technical implementation of this vulnerability lies in the server's authentication routine which fails to normalize error responses regardless of whether a username exists in the system. When an authentication attempt is made with a non-existent username, the server returns a specific error message indicating that the username is invalid, whereas valid usernames that fail authentication due to incorrect passwords generate different error responses. This differential handling creates a side-channel attack vector where attackers can systematically test usernames and observe the server's response patterns to determine which accounts are legitimate. The vulnerability aligns with CWE-305 authentication weakness category and specifically manifests as an improper error handling issue that violates fundamental security principles of maintaining consistent error responses to prevent information leakage.
The operational impact of this vulnerability extends beyond simple account enumeration, as it provides attackers with a foundation for more sophisticated attacks including password spraying, credential stuffing, and targeted brute-force attempts. Once an attacker has identified valid usernames through this enumeration process, they can focus their efforts on cracking passwords for specific accounts rather than attempting to guess across all possible usernames. This significantly reduces the computational resources and time required for successful unauthorized access. The vulnerability also creates opportunities for social engineering attacks as attackers can use the confirmed usernames to craft more convincing phishing attempts or to identify high-value targets within the organization's user base. From an attacker's perspective, this vulnerability directly maps to ATT&CK technique T1078 credential access, specifically targeting valid accounts through credential compromise.
Mitigation strategies for CVE-2023-47102 should prioritize immediate implementation of consistent error handling across all authentication attempts to prevent any distinguishable responses that could aid enumeration efforts. Organizations should configure the UrBackup Server to return identical error messages for both non-existent and invalid username attempts, ensuring that all authentication failures appear identical to external observers. Additionally, implementing account lockout mechanisms with intelligent rate limiting can prevent automated enumeration attempts from succeeding within reasonable timeframes. Network-level protections such as ip address blocking for repeated failed authentication attempts and the deployment of intrusion detection systems can further enhance security posture. The most effective long-term solution involves upgrading to a patched version of UrBackup Server where the authentication routine has been properly hardened to eliminate the information disclosure vulnerability. Security teams should also conduct comprehensive testing to verify that all authentication endpoints maintain consistent response patterns and implement proper logging to detect potential enumeration attempts.