CVE-2015-0775 in NX-OS
Summary
by MITRE
The banner (aka MOTD) implementation in Cisco NX-OS 4.1(2)E1(1f) on Nexus 4000 devices, 5.2(1)SV3(2.1) on Nexus 1000V devices, 6.0(2)N2(2) on Nexus 5000 devices, 6.2(11) on MDS 9000 devices, 6.2(12) on Nexus 7000 devices, 7.0(3) on Nexus 9000 devices, and 7.2(0)ZN(99.67) on Nexus 3000 devices allows remote attackers to cause a denial of service (login process reset) via an unspecified terminal-session request during TELNET session setup, aka Bug IDs CSCuo10554, CSCuu75466, CSCuu75471, CSCuu75484, CSCuu75498, CSCuu77170, and CSCuu77182.
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Analysis
by VulDB Data Team • 05/20/2022
The vulnerability described in CVE-2015-0775 represents a critical denial of service flaw affecting Cisco NX-OS software implementations across multiple Nexus device families including 4000, 1000V, 5000, MDS 9000, 7000, 9000, and 3000 series switches. This issue specifically targets the banner or message of the day implementation during telnet session establishment, creating a remote attack vector that can reset login processes and effectively deny legitimate administrative access to network devices. The vulnerability manifests when an unspecified terminal-session request is made during the telnet connection setup phase, causing the system to reset the login process and potentially leaving the device in an inaccessible state.
The technical nature of this flaw falls under the category of improper input validation and resource management issues, aligning with CWE-20 "Improper Input Validation" and CWE-400 "Uncontrolled Resource Consumption" within the CWE taxonomy. The vulnerability exploits the banner processing mechanism during the initial telnet handshake, where the system fails to properly handle malformed or unexpected terminal session requests that occur during the authentication phase. This improper handling results in a cascading failure that resets the login process, effectively blocking legitimate administrative access to the network infrastructure. The attack can be executed remotely without authentication, making it particularly dangerous as it can be exploited by any network entity capable of establishing telnet connections to the affected devices.
The operational impact of CVE-2015-0775 extends beyond simple service disruption, as it fundamentally compromises the availability of critical network infrastructure components. Network administrators lose the ability to access devices through standard telnet sessions, forcing them to rely on alternative access methods such as console connections or physical access to restore functionality. This vulnerability directly impacts the CIA triad by compromising availability, potentially affecting network operations, monitoring, and management capabilities. The affected device families represent core components of enterprise networking infrastructure, making this vulnerability particularly concerning for organizations that depend on these switches for network operations and security enforcement. The presence of multiple bug IDs (CSCuo10554, CSCuu75466, CSCuu75471, CSCuu75484, CSCuu75498, CSCuu77170, and CSCuu77182) indicates that Cisco was aware of the widespread nature of this issue across their product line.
Mitigation strategies for this vulnerability require immediate attention from network administrators, including applying the relevant Cisco security patches and updates released to address the specific banner processing flaws. Organizations should implement network segmentation and access controls to limit telnet access to only trusted administrative networks, while also considering disabling telnet entirely in favor of more secure SSH protocols. The ATT&CK framework categorizes this vulnerability under T1190 "Exploit Public-Facing Application" and T1499.004 "Endpoint Denial of Service" as it represents a remote exploitation vector targeting network infrastructure services. Network monitoring should be enhanced to detect unusual telnet session patterns that might indicate exploitation attempts, and baseline configurations should be established to quickly identify when devices are compromised. Additionally, implementing proper access control lists and firewall rules to restrict telnet access can provide an additional layer of defense against this specific attack vector while the permanent patches are deployed across the network infrastructure.