CVE-1999-0734 in ACS
Summary
by MITRE
A default configuration of CiscoSecure Access Control Server (ACS) allows remote users to modify the server database without authentication.
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Analysis
by VulDB Data Team • 04/19/2026
The vulnerability identified as CVE-1999-0734 represents a critical authentication bypass flaw in CiscoSecure Access Control Server version 3.1 and earlier. This issue stems from improper default security configurations that fail to enforce proper access controls during database modification operations. The vulnerability allows remote attackers to perform unauthorized database changes without providing valid credentials, fundamentally undermining the security posture of the access control infrastructure. The flaw exists in the default installation settings where administrative database operations remain accessible to any remote user who can establish network connectivity to the server.
This vulnerability directly maps to CWE-284 Access Control Issues, specifically manifesting as insufficient access control mechanisms that permit unauthorized modification of critical system components. The technical implementation flaw occurs at the network service level where the server fails to validate user credentials before processing database modification requests. Attackers can exploit this by connecting to the affected service and executing database operations that should require administrative authentication, potentially leading to complete compromise of the access control system. The vulnerability affects the integrity and confidentiality of the entire access control infrastructure as it allows modification of user credentials, access policies, and system configurations.
The operational impact of this vulnerability is severe and far-reaching for organizations relying on CiscoSecure ACS for network access control. Remote attackers can manipulate user accounts, modify access permissions, disable security controls, and potentially gain persistent access to network resources. This vulnerability undermines the fundamental purpose of an access control server which is to enforce security policies and authenticate users. The default nature of the vulnerability means that organizations may unknowingly operate in a compromised state for extended periods, as the issue persists across all installations until manually addressed. This creates a significant risk for network security as the attacker can essentially take control of the access control system itself.
Mitigation strategies for CVE-1999-0734 require immediate administrative action to address the default configuration issues. Organizations should implement proper access control measures by configuring authentication requirements for all database modification operations, disabling unnecessary services, and applying the latest security patches from Cisco. Network segmentation should be implemented to limit access to the ACS server to authorized administrative networks only. The recommended approach involves reviewing and modifying default configurations to enforce strong authentication requirements for all administrative functions. Additionally, organizations should implement network monitoring to detect unauthorized access attempts and establish regular security audits to verify proper configuration. The solution aligns with ATT&CK technique T1078 Valid Accounts and T1566 Phishing, as attackers can leverage this vulnerability to establish persistent access and potentially escalate privileges within the network infrastructure.