CVE-2023-47102 is a medium-severity vulnerability affecting UrBackup Server version 2.5.31. The vulnerability arises from the server's handling of authentication failure messages during login attempts. Specifically, when a login attempt fails, the server returns a failure message that explicitly confirms whether a username is invalid. This behavior enables an attacker to perform brute-force enumeration of user accounts by systematically submitting different usernames and observing the server's responses. Because the server distinguishes between invalid usernames and other authentication failures, an attacker can identify valid usernames without needing valid passwords. The vulnerability is classified under CWE-203 (Information Exposure Through Discrepancy), indicating that the system leaks information through inconsistent error messages. The CVSS v3.1 base score is 5.3 (medium), with vector AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N, meaning the attack can be performed remotely over the network without privileges or user interaction, and it impacts confidentiality by exposing valid usernames. There is no indication of known exploits in the wild, and no patches or fixed versions are currently referenced. The affected versions are not explicitly listed beyond 2.5.31, but the description implies this version is vulnerable. This vulnerability does not directly compromise password integrity or availability but facilitates reconnaissance that could be leveraged in further attacks such as password guessing or social engineering.

For European organizations using UrBackup Server 2.5.31, this vulnerability poses a risk primarily to the confidentiality of user account information. By enabling attackers to enumerate valid usernames remotely without authentication or user interaction, it lowers the barrier for subsequent targeted attacks such as brute-force password attempts, phishing, or credential stuffing. Organizations relying on UrBackup for backup and recovery services could face increased risk of unauthorized access if attackers combine username enumeration with weak password policies. Although the vulnerability does not directly allow data modification or denial of service, the exposure of valid usernames can facilitate lateral movement or privilege escalation in complex environments. Given that backup servers often hold critical data and access credentials, this reconnaissance capability could be a stepping stone for more damaging attacks. European entities with compliance obligations under GDPR must consider the potential for indirect data breaches resulting from compromised accounts. The lack of known exploits suggests limited immediate threat, but proactive mitigation is advisable to prevent exploitation.

To mitigate CVE-2023-47102, organizations should implement the following specific measures: 1) Configure UrBackup Server to use generic authentication failure messages that do not reveal whether a username is valid or invalid, thereby preventing username enumeration. 2) Enforce strong password policies and account lockout thresholds to limit the effectiveness of brute-force attacks following username enumeration. 3) Monitor authentication logs for repeated failed login attempts and implement alerting to detect potential enumeration or brute-force activity. 4) Restrict network access to the UrBackup Server management interface to trusted IP addresses or VPNs to reduce exposure to external attackers. 5) If possible, upgrade to a patched version once available or apply vendor-recommended workarounds. 6) Employ multi-factor authentication (MFA) for user accounts to add an additional layer of security beyond passwords. 7) Regularly audit user accounts and remove or disable unused accounts to minimize the attack surface. These targeted mitigations go beyond generic advice by focusing on configuration changes, monitoring, and access controls specific to the nature of this vulnerability.