CVE-2013-6979 in IOS XE
Summary
by MITRE
The VTY authentication implementation in Cisco IOS XE 03.02.xxSE and 03.03.xxSE incorrectly relies on the Linux-IOS internal-network configuration, which allows remote attackers to bypass authentication by leveraging access to a 192.168.x.2 source IP address, aka Bug ID CSCuj90227.
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Analysis
by VulDB Data Team • 06/04/2021
The vulnerability described in CVE-2013-6979 represents a critical authentication flaw within Cisco IOS XE software versions 03.02.xxSE and 03.03.xxSE that affects the Virtual Teletypewriter (VTY) access mechanism. This issue stems from an improper implementation of authentication controls that creates a security bypass condition, allowing unauthorized remote attackers to gain access to network devices without proper credentials. The vulnerability specifically targets the VTY line configuration which is used for remote access to Cisco routers and switches through telnet or ssh protocols, making it particularly dangerous for network administrators who rely on these access methods for device management.
The technical root cause of this vulnerability lies in the improper handling of source IP address validation within the Linux-IOS internal network configuration framework. When a remote attacker establishes a connection to a vulnerable Cisco device, the system incorrectly evaluates the source IP address and allows access when the connecting IP matches the specific pattern of 192.168.x.2 addresses. This misconfiguration creates an authentication bypass where legitimate authentication mechanisms are effectively circumvented, enabling unauthorized access to the device's command-line interface. The vulnerability operates at the network layer where source address validation should normally enforce strict access controls, but instead provides a backdoor for attackers with specific IP address ranges.
The operational impact of this vulnerability extends beyond simple unauthorized access, as it provides attackers with potential entry points for broader network compromise. Network administrators who rely on VTY access for device management face significant risk when their systems are vulnerable to this attack, as it allows for complete device control without proper authentication. The vulnerability particularly affects organizations that may have legacy configurations or specific network topologies where 192.168.x.2 IP addresses are used in their internal networks, creating an environment where attackers can exploit this flaw without requiring additional privileges or credentials. This authentication bypass can lead to configuration changes, data exfiltration, and potential use as a pivot point for attacking other systems within the network.
Organizations should implement immediate mitigations including updating to patched versions of Cisco IOS XE software where the vulnerability has been addressed through proper source IP validation mechanisms. Network segmentation and access control measures should be strengthened to prevent unauthorized access to devices with vulnerable configurations, while monitoring systems should be enhanced to detect unusual connection patterns from 192.168.x.2 addresses. The vulnerability aligns with CWE-287 which addresses improper authentication issues, and can be mapped to ATT&CK technique T1078 which covers valid accounts and legitimate credentials for persistence and privilege escalation. Regular security assessments and network configuration reviews should be conducted to identify and remediate similar authentication bypass vulnerabilities that could exist in other network components or software implementations.