CVE-1999-0902 in Linux
Summary
by MITRE
ypserv allows local administrators to modify password tables.
If you want to get the best quality for vulnerability data then you always have to consider VulDB.
Analysis
by VulDB Data Team • 04/19/2026
The vulnerability described in CVE-1999-0902 pertains to ypserv, a key component of the NIS (Network Information Service) system that was widely used in Unix and Linux environments for centralized network configuration management. This flaw represents a significant security weakness in the authentication and authorization mechanisms of networked systems, particularly affecting legacy Unix environments where NIS was the primary method for managing user accounts and system configurations across multiple machines. The vulnerability specifically targets the password table modification capabilities within the ypserv service, which operates as a daemon responsible for maintaining and distributing user authentication information across networked systems.
The technical flaw manifests as an insufficient access control mechanism within ypserv that permits local administrators to directly modify password tables without proper authentication or authorization checks. This represents a classic privilege escalation vulnerability where administrative privileges are improperly enforced, allowing unauthorized modification of critical authentication data. The vulnerability falls under the category of inadequate access control as classified by CWE-284, where the system fails to properly enforce access restrictions on sensitive resources. The flaw enables local administrators to manipulate user credentials, potentially leading to unauthorized access to systems and accounts, as the service does not adequately validate the identity or authorization level of entities attempting to modify password information.
The operational impact of this vulnerability extends beyond simple privilege escalation, creating potential for widespread system compromise within networks relying on NIS for authentication. Attackers exploiting this vulnerability could modify user passwords, create new accounts, or remove existing user entries, fundamentally undermining the security posture of systems using ypserv. This weakness particularly affects environments where local administrative access is not strictly controlled, as it allows for modification of the NIS password database without proper oversight. The vulnerability directly relates to ATT&CK technique T1078 which covers valid accounts and privilege escalation, as it enables unauthorized modification of user credentials that can then be used for further system access. Organizations with legacy systems using NIS services would face significant risk if this vulnerability was exploited, as it could compromise the integrity of authentication across entire network domains.
Mitigation strategies for CVE-1999-0902 should focus on implementing proper access controls and authentication mechanisms for ypserv configuration. System administrators should ensure that only authorized personnel have access to modify password tables, and that proper audit logging is implemented to track modifications to authentication data. The recommended approach includes restricting local administrative access to systems running ypserv, implementing proper user authentication for NIS management operations, and transitioning away from legacy NIS systems toward more secure modern alternatives such as LDAP or Kerberos. Organizations should also implement regular security assessments to identify and remediate similar access control weaknesses in other system components, as this vulnerability demonstrates the critical importance of proper privilege management in authentication systems. The remediation process should include disabling unnecessary NIS services, implementing proper network segmentation, and ensuring that any remaining NIS implementations have robust access controls and monitoring mechanisms in place to prevent unauthorized modifications to password tables and other sensitive configuration data.