CVE-2017-3878 in NX-OS
Summary
by MITRE
A Denial of Service vulnerability in the Telnet remote login functionality of Cisco NX-OS Software running on Cisco Nexus 9000 Series Switches could allow an unauthenticated, remote attacker to cause a Telnet process used for login to terminate unexpectedly and the login attempt to fail. There is no impact to user traffic flowing through the device. Affected Products: This vulnerability affects Cisco Nexus 9000 Series Switches that are running Cisco NX-OS Software and are configured to allow remote Telnet connections to the device. More Information: CSCux46778. Known Affected Releases: 7.0(3)I3(0.170). Known Fixed Releases: 7.0(3)I3(1) 7.0(3)I3(0.257) 7.0(3)I3(0.255) 7.0(3)I2(2e) 7.0(3)F1(1.22) 7.0(3)F1(1).
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Analysis
by VulDB Data Team • 12/25/2024
The vulnerability described in CVE-2017-3878 represents a denial of service condition within the Telnet remote login implementation of Cisco NX-OS Software on Nexus 9000 Series Switches. This flaw specifically targets the Telnet process responsible for handling remote authentication attempts, creating a scenario where unauthorized attackers can disrupt legitimate administrative access to network infrastructure. The vulnerability manifests when an unauthenticated remote attacker exploits a weakness in the Telnet service that causes the login process to terminate unexpectedly, resulting in failed authentication attempts without affecting the actual data traffic passing through the device.
Technical analysis reveals that this vulnerability stems from improper handling of Telnet connection states or authentication sequences within the NX-OS Software implementation. The affected software versions, particularly 7.0(3)I3(0.170), contain a flaw that allows attackers to send specially crafted Telnet protocol sequences that trigger an abrupt termination of the Telnet process. This behavior aligns with CWE-400, which categorizes excessive resource consumption and improper error handling as common causes of denial of service vulnerabilities. The flaw does not permit privilege escalation or unauthorized access to network resources, but rather focuses on disrupting the availability of the Telnet service itself, making it difficult for legitimate administrators to perform remote maintenance or configuration tasks.
From an operational perspective, this vulnerability presents significant risk to network availability and management capabilities. Network administrators who rely on Telnet for remote access to their Nexus 9000 switches face potential disruption of their management workflows, particularly in environments where automated monitoring or remote troubleshooting is required. The impact extends beyond simple inconvenience as it can interfere with incident response procedures, system maintenance windows, and routine administrative tasks that require remote access. The vulnerability's remote nature means that attackers do not need physical access or local network privileges to exploit it, making it particularly dangerous in environments where network security is already a concern. According to ATT&CK framework category T1499, this vulnerability represents a denial of service attack that specifically targets network infrastructure availability.
Mitigation strategies for this vulnerability include immediate deployment of the patched software versions provided by Cisco, specifically versions 7.0(3)I3(1), 7.0(3)I3(0.257), 7.0(3)I3(0.255), 7.0(3)I2(2e), 7.0(3)F1(1.22), and 7.0(3)F1(1). Organizations should also consider disabling Telnet access entirely and transitioning to more secure remote access protocols such as SSH, which provides encrypted communication channels and better authentication mechanisms. Network segmentation and access control measures should be implemented to limit exposure of Telnet services to trusted networks only, while monitoring systems should be configured to detect unusual Telnet connection patterns or repeated failed authentication attempts that might indicate exploitation attempts. The vulnerability serves as a reminder of the importance of maintaining current software versions and implementing defense-in-depth strategies to protect critical network infrastructure components.