CVE-2015-0607 in IOS
Summary
by MITRE
The Authentication Proxy feature in Cisco IOS does not properly handle invalid AAA return codes from RADIUS and TACACS+ servers, which allows remote attackers to bypass authentication in opportunistic circumstances via a connection attempt that triggers an invalid code, as demonstrated by a connection attempt with a blank password, aka Bug IDs CSCuo09400 and CSCun16016.
Once again VulDB remains the best source for vulnerability data.
Analysis
by VulDB Data Team • 12/02/2024
The vulnerability described in CVE-2015-0607 resides within Cisco IOS Authentication Proxy functionality, specifically targeting the handling of AAA (Authentication, Authorization, and Accounting) return codes from RADIUS and TACACS+ servers. This weakness represents a critical flaw in the authentication process that can be exploited by remote attackers to bypass authentication mechanisms under specific conditions. The vulnerability manifests when the authentication proxy receives invalid AAA return codes from backend authentication servers, creating an opportunity for unauthorized access to network resources. The issue is particularly concerning because it operates in an opportunistic manner, meaning that attackers can exploit it during connection attempts that generate invalid authentication responses, making the vulnerability difficult to detect and prevent through standard security measures.
The technical implementation of this vulnerability stems from insufficient validation and error handling within the IOS authentication proxy module. When RADIUS or TACACS+ servers return unexpected or invalid AAA codes during the authentication process, the Cisco IOS system fails to properly process these responses and instead allows the connection to proceed without proper authentication verification. This behavior creates a security gap where legitimate authentication failures are treated as successful authentications, effectively allowing unauthorized users to gain access to protected network resources. The vulnerability is particularly evident when attackers attempt connections with blank passwords or other invalid credentials that trigger the specific error conditions. According to CWE classification, this vulnerability maps to CWE-284 Access Control Bypass, as it allows unauthorized access to network resources through improper access control enforcement. The operational impact extends beyond simple authentication bypass, as it can enable attackers to establish unauthorized network sessions and potentially escalate privileges within the affected network infrastructure.
The exploitation of CVE-2015-0607 requires attackers to understand the specific conditions under which invalid AAA codes are generated, particularly when attempting connections with blank or malformed credentials. Attackers can leverage this vulnerability by initiating connection attempts that trigger invalid return codes from the authentication servers, thereby creating a window of opportunity to bypass authentication mechanisms. This exploitation technique aligns with ATT&CK framework tactic TA0006 Credential Access and technique T1110.001 Brute Force, as it exploits weaknesses in authentication handling rather than direct credential theft. The vulnerability affects Cisco IOS devices including routers, switches, and other network infrastructure components that rely on RADIUS or TACACS+ authentication for access control. Organizations implementing these authentication protocols are at risk, particularly those with legacy IOS versions or devices that have not received the appropriate security patches. The opportunistic nature of the exploit means that detection is challenging since the authentication bypass occurs only under specific error conditions, making it difficult to identify through standard network monitoring or intrusion detection systems.
Mitigation strategies for CVE-2015-0607 primarily involve applying the official Cisco security patches and updates that address the improper AAA return code handling within the Authentication Proxy feature. Network administrators should prioritize updating all affected IOS devices to versions that contain the necessary fixes, which typically involve enhanced validation of AAA server responses and more robust error handling procedures. Additionally, implementing network segmentation and access control measures can help limit the potential impact of successful exploitation attempts. Organizations should also consider deploying additional monitoring solutions that can detect unusual authentication patterns or error conditions that might indicate exploitation attempts. The recommended approach includes configuring devices to properly log authentication failures and implementing alerting mechanisms for anomalous AAA server responses. Security teams should conduct regular vulnerability assessments and penetration testing to identify and remediate similar authentication bypass vulnerabilities within their network infrastructure. Given the nature of the vulnerability and its relationship to AAA protocols, organizations should also review their overall authentication architecture and consider implementing multi-factor authentication mechanisms as an additional security layer to reduce the risk of successful exploitation.