CVE-2013-5509 in Appliance
Summary
by MITRE
The SSL implementation in Cisco Adaptive Security Appliance (ASA) Software 9.0 before 9.0(2.6) and 9.1 before 9.1(2) allows remote attackers to bypass authentication, and obtain VPN access or administrative access, via a crafted X.509 client certificate, aka Bug ID CSCuf52468.
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Analysis
by VulDB Data Team • 05/26/2021
The vulnerability described in CVE-2013-5509 represents a critical authentication bypass flaw within Cisco Adaptive Security Appliance (ASA) software versions 9.0 prior to 9.0(2.6) and 9.1 prior to 9.1(2). This weakness specifically targets the SSL implementation used for VPN authentication processes, creating a pathway for remote attackers to circumvent the security controls designed to protect network access. The vulnerability manifests through the improper handling of X.509 client certificates during the authentication handshake process, allowing malicious actors to craft specially formatted certificates that bypass the intended verification mechanisms. This issue directly impacts the integrity of the authentication system by enabling unauthorized access to both VPN services and administrative functions of the affected ASA devices.
The technical flaw stems from insufficient validation of X.509 client certificates within the SSL implementation of the affected Cisco ASA versions. When a client attempts to establish a secure connection through the VPN service, the system should rigorously verify the certificate's authenticity, validity, and proper authorization status before granting access. However, the vulnerability allows attackers to exploit weaknesses in this certificate validation process, potentially enabling them to present forged or improperly configured certificates that are accepted as legitimate. This behavior violates fundamental security principles of certificate-based authentication and creates a direct pathway for privilege escalation. The flaw operates at the protocol level within the SSL/TLS implementation, making it particularly dangerous as it can be exploited without requiring local access or prior knowledge of valid credentials, aligning with CWE-295 which addresses issues related to certificate validation and trust management.
The operational impact of this vulnerability extends beyond simple unauthorized access to encompass potential full administrative control over affected network infrastructure. Remote attackers who successfully exploit this vulnerability can gain unrestricted access to VPN services, potentially allowing them to traverse internal networks, access sensitive data, and perform administrative functions on the ASA device itself. This compromise can lead to widespread network infiltration, data exfiltration, and disruption of business continuity. The vulnerability's remote exploitability means that attackers can target these systems from anywhere on the internet without requiring physical access or insider knowledge. Organizations relying on Cisco ASA for network security are particularly vulnerable, as this flaw undermines the core security model that depends on strong authentication and authorization controls. The impact is amplified when considering that many organizations use these devices as primary network security gateways, making the compromise of such systems potentially catastrophic for network security posture and compliance requirements.
Mitigation strategies for CVE-2013-5509 primarily focus on immediate software updates and configuration hardening measures. Organizations should prioritize upgrading their Cisco ASA software to versions 9.0(2.6) or 9.1(2) and later, which contain the necessary patches to address the certificate validation flaw. In addition to software updates, network administrators should implement enhanced monitoring of authentication events and establish strict certificate management policies. The vulnerability's classification under ATT&CK technique T1078.004 highlights the importance of implementing robust certificate-based authentication controls and regular security assessments. Security teams should also consider implementing additional access controls such as multi-factor authentication, network segmentation, and enhanced logging of VPN authentication attempts to detect potential exploitation attempts. Regular security audits and vulnerability assessments should be conducted to identify any other potential weaknesses in the authentication infrastructure that could be exploited in conjunction with this vulnerability. Organizations should also review their certificate authority configurations and ensure that proper certificate lifecycle management procedures are in place to prevent unauthorized certificate issuance or use.