CVE-2005-2105 in IOS
Summary
by MITRE
Cisco IOS 12.2T through 12.4 allows remote attackers to bypass Authentication, Authorization, and Accounting (AAA) RADIUS authentication, if the fallback method is set to none, via a long username.
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Analysis
by VulDB Data Team • 06/30/2025
The vulnerability described in CVE-2005-2105 represents a critical weakness in Cisco IOS software versions 12.2T through 12.4 that directly impacts the security of network access control mechanisms. This flaw specifically targets the Authentication, Authorization, and Accounting framework within Cisco's networking equipment, creating a potential pathway for unauthorized access when the fallback authentication method is configured to none. The vulnerability stems from improper handling of user input during the RADIUS authentication process, where the system fails to properly validate or truncate excessively long username strings.
The technical implementation of this vulnerability occurs when a malicious actor crafts a specially formatted username that exceeds the expected buffer size allocated for authentication processing. When the Cisco IOS device receives this oversized username, it processes the input without proper bounds checking, allowing the authentication mechanism to bypass normal validation procedures. This behavior creates a condition where the system may inadvertently grant access to users who should be denied entry, particularly when the fallback authentication method is disabled. The flaw is classified under CWE-121 as a buffer overflow condition, though it manifests specifically within the authentication context rather than causing direct system crashes.
The operational impact of this vulnerability extends beyond simple unauthorized access, potentially enabling attackers to establish persistent network presence while evading normal security controls. When configured with fallback set to none, network administrators may believe their systems are properly secured against unauthorized access, unaware that this specific vulnerability allows bypassing the primary authentication mechanism entirely. The attack vector requires remote access to the network device and knowledge of the specific authentication configuration, making it particularly dangerous in environments where network access control is critical. This vulnerability directly contradicts the fundamental security principle of least privilege and can result in complete compromise of network access controls.
Mitigation strategies for this vulnerability require immediate attention from network administrators, including implementing proper AAA configuration with fallback authentication methods enabled and ensuring all Cisco IOS devices are updated to versions that address this specific buffer handling issue. Organizations should also consider implementing network segmentation and additional access controls to limit the potential impact of successful exploitation. The vulnerability aligns with ATT&CK technique T1078 which covers valid accounts and privilege escalation, as it allows attackers to bypass authentication mechanisms and potentially gain elevated access rights. Regular security assessments and proper configuration management practices are essential to prevent exploitation of this type of authentication bypass vulnerability.