CVE-2004-1099 in Secure ACS
Summary
by MITRE
Cisco Secure Access Control Server for Windows (ACS Windows) and Cisco Secure Access Control Server Solution Engine (ACS Solution Engine) 3.3.1, when the EAP-TLS protocol is enabled, does not properly handle expired or untrusted certificates, which allows remote attackers to bypass authentication and gain unauthorized access via a "cryptographically correct" certificate with valid fields such as the username.
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Analysis
by VulDB Data Team • 06/30/2019
The vulnerability described in CVE-2004-1099 represents a critical authentication bypass flaw affecting Cisco Secure Access Control Server implementations across both Windows and Solution Engine platforms. This weakness specifically manifests when the EAP-TLS protocol is enabled, creating a scenario where the system fails to properly validate certificate trust chains and expiration dates. The vulnerability stems from inadequate certificate validation mechanisms that permit malicious actors to exploit the authentication process by presenting certificates that appear cryptographically sound but contain compromised or unauthorized credentials.
The technical flaw operates through a certificate validation bypass mechanism where the ACS systems accept certificates that meet basic cryptographic requirements while ignoring critical trust indicators such as certificate expiration dates, Certificate Authority validation, or certificate revocation status. This allows attackers to craft certificates with valid fields including usernames that align with legitimate system requirements, yet these certificates are accepted due to the flawed validation logic. The vulnerability specifically impacts the EAP-TLS authentication framework which is designed to provide secure network access through mutual authentication between client and server using digital certificates.
Operationally, this vulnerability creates a significant security risk by enabling remote attackers to bypass authentication controls entirely. Attackers can exploit this weakness to gain unauthorized network access without requiring legitimate credentials, effectively undermining the entire authentication infrastructure. The impact extends beyond simple unauthorized access as it can lead to privilege escalation, lateral movement within networks, and potential data breaches. Organizations relying on EAP-TLS for network access control face severe exposure since the vulnerability allows attackers to impersonate legitimate users and systems within the network environment.
The security implications of this vulnerability align with CWE-295 which addresses improper certificate validation and certificate trust chain issues. From an ATT&CK framework perspective, this vulnerability maps to privilege escalation and initial access techniques, specifically leveraging credential access methods to bypass authentication controls. Organizations should implement immediate mitigations including disabling EAP-TLS when not required, implementing proper certificate management policies, and deploying certificate monitoring solutions. Additionally, updating to patched versions of Cisco ACS software, implementing network segmentation, and conducting regular certificate audits are essential remediation steps. The vulnerability also highlights the importance of proper certificate lifecycle management and the need for robust certificate validation procedures that consider not just cryptographic strength but also trust chain integrity and expiration status.