CVE-2015-4185 in IOS
Summary
by MITRE
The TCL interpreter in Cisco IOS 15.2 does not properly maintain the vty state, which allows local users to gain privileges by starting a session very soon after a TCL script execution, aka Bug ID CSCuq24202.
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Analysis
by VulDB Data Team • 05/21/2022
The vulnerability described in CVE-2015-4185 represents a critical privilege escalation flaw within Cisco IOS 15.2 systems that specifically affects the Terminal Control Language (TCL) interpreter implementation. This issue stems from improper state management within the virtual terminal line (vty) session handling mechanism, creating a window of opportunity for malicious local users to exploit the system's security controls. The vulnerability manifests when a user attempts to establish a new vty session immediately following the execution of a TCL script, exploiting a race condition in the state transition process that should normally prevent concurrent session management.
The technical root cause of this vulnerability lies in the failure of the TCL interpreter to properly maintain session state information during the transition between script execution and interactive terminal sessions. When a TCL script runs, the system should ensure that all session state variables are properly reset or maintained before allowing new connections. However, in this case, the vty state management does not adequately synchronize these transitions, allowing an attacker to potentially manipulate session parameters and gain elevated privileges. This flaw directly relates to CWE-362, which addresses race conditions in security-critical operations, and specifically targets the improper handling of concurrent access to shared resources.
The operational impact of this vulnerability is significant as it allows local attackers with basic user privileges to escalate their access level within the network device. The privilege escalation occurs through the manipulation of the vty session state, potentially enabling attackers to gain administrative access to the Cisco IOS device. This could result in complete compromise of the network infrastructure, allowing unauthorized users to modify device configurations, access sensitive network data, or establish persistent backdoors. The vulnerability is particularly dangerous because it requires minimal privileges to exploit and can be triggered through normal operational procedures, making it difficult to detect and prevent.
Mitigation strategies for CVE-2015-4185 should include immediate deployment of Cisco's recommended security patches and updates that address the vty state management issue. Network administrators should implement strict access controls and monitor for unusual session creation patterns that might indicate exploitation attempts. The vulnerability aligns with ATT&CK technique T1068, which covers local privilege escalation through race conditions, and organizations should consider implementing additional monitoring controls to detect anomalous session behavior. System hardening measures should also include disabling unnecessary TCL scripting capabilities where possible and implementing proper session timeout mechanisms to reduce the window of opportunity for exploitation. Regular security assessments and vulnerability scanning should be conducted to identify similar state management issues in other network infrastructure components.