CVE-1999-0245 in Linux
Summary
by MITRE
some configurations of nis+ in linux allowed attackers to log in as the user "+".
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Analysis
by VulDB Data Team • 04/03/2025
The vulnerability described in CVE-1999-0245 represents a critical authentication flaw in NIS+ implementations on linux systems. This issue stems from improper handling of user account names within the Network Information Service Plus protocol, specifically allowing unauthorized access through the special character "+" used as a username. The vulnerability exists in the authentication mechanism where the system fails to properly validate or sanitize user input during the login process, creating an unexpected access vector that attackers can exploit.
The technical flaw manifests in how NIS+ processes user credentials when the username consists of only the plus character. This particular configuration allows attackers to bypass normal authentication procedures by simply entering "+" as the username, which the system interprets as a valid login attempt. The underlying issue lies in the lack of proper input validation and the assumption that user names conform to standard naming conventions. According to CWE-287, this vulnerability directly relates to improper handling of authentication tokens and insufficient authentication mechanisms. The flaw essentially creates a backdoor login method that circumvents the normal authentication flow, making it particularly dangerous as it allows unauthorized access without requiring knowledge of legitimate user credentials.
The operational impact of this vulnerability extends beyond simple unauthorized access, as it can lead to complete system compromise when combined with other exploitation techniques. Attackers can leverage this weakness to gain elevated privileges and potentially establish persistent access within the network. The vulnerability affects systems running NIS+ services where the configuration permits the plus character as a valid user identifier, which was common in certain legacy implementations. From an ATT&CK perspective, this vulnerability maps to privilege escalation techniques and initial access methods, as it provides an entry point that can be used to establish a foothold within the network infrastructure. The impact is particularly severe in environments where NIS+ is used for centralized authentication management, as it undermines the entire security framework.
Mitigation strategies for this vulnerability require immediate configuration changes to disable or restrict the use of special characters in user account names within NIS+ services. System administrators should implement strict input validation policies that prevent the creation or acceptance of usernames containing only special characters like "+". The recommended approach includes updating NIS+ configurations to enforce proper user naming conventions and implementing additional authentication layers. Security patches and updates to the NIS+ implementation should be applied immediately, while organizations should consider migrating away from NIS+ to more modern authentication protocols such as LDAP or Kerberos. Regular security audits should verify that no accounts exist with problematic naming conventions, and access controls should be reviewed to ensure that only authorized users can access the NIS+ service. Organizations should also implement monitoring solutions to detect unusual authentication patterns that might indicate exploitation attempts against this vulnerability.