CVE-2000-1056 in Secure Access Control Server
Summary
by MITRE
CiscoSecure ACS Server 2.4(2) and earlier allows remote attackers to bypass LDAP authentication on the server if the LDAP server allows null passwords.
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Analysis
by VulDB Data Team • 04/06/2019
The vulnerability described in CVE-2000-1056 represents a critical authentication bypass flaw in CiscoSecure Access Control Server versions 2.4(2) and earlier. This issue specifically affects the LDAP authentication mechanism used by the CiscoSecure ACS server, which is designed to provide centralized authentication services for network access control. The vulnerability arises from the server's improper handling of LDAP authentication responses when the LDAP directory service permits null password authentication attempts. The flaw exists in the server's processing logic where it fails to properly validate or reject authentication requests that contain null passwords, creating an exploitable condition that allows unauthorized users to gain access to network resources without proper authentication credentials.
The technical implementation of this vulnerability stems from the CiscoSecure ACS server's insufficient validation of LDAP responses during the authentication process. When the LDAP server configuration allows null passwords to be accepted as valid authentication credentials, the CiscoSecure ACS server does not properly filter or reject these authentication attempts. This behavior creates a security gap where attackers can exploit the system by crafting authentication requests that leverage null password credentials, effectively bypassing the intended authentication controls. The vulnerability specifically impacts the server's LDAP integration component and occurs at the point where authentication decisions are made based on LDAP server responses, making it a direct authentication bypass issue that falls under CWE-287 which addresses improper authentication.
The operational impact of this vulnerability is significant as it allows remote attackers to completely circumvent the authentication mechanisms that are supposed to protect network access. An attacker who can reach the CiscoSecure ACS server over the network can exploit this weakness to gain unauthorized access to network resources that would normally require legitimate authentication credentials. This could lead to unauthorized network access, privilege escalation, and potential data compromise depending on the access controls configured within the network. The remote nature of the attack means that exploitation does not require physical access to the network infrastructure, making it particularly dangerous in environments where network access control is critical for security. The vulnerability also aligns with ATT&CK technique T1078 which covers valid accounts and credential access, as it allows attackers to use compromised or null credentials to gain system access.
Mitigation strategies for this vulnerability involve multiple layers of security controls and configuration changes. Organizations should immediately upgrade to CiscoSecure ACS Server versions that have patched this vulnerability, as Cisco released updates specifically addressing this issue. Network administrators should review and tighten LDAP server configurations to ensure that null passwords are not permitted as valid authentication credentials. The recommended approach includes implementing proper LDAP server policies that reject null password authentication attempts and configuring the CiscoSecure ACS server to enforce stricter authentication validation. Additionally, network segmentation and access controls should be implemented to limit exposure of the vulnerable system to unauthorized network access. Security monitoring should be enhanced to detect unusual authentication patterns that might indicate exploitation attempts, and regular security assessments should be conducted to verify that the configuration changes have been properly implemented and are effective in preventing unauthorized access.