CVE-2018-15369 in IOS
Summary
by MITRE
A vulnerability in the TACACS+ client subsystem of Cisco IOS Software and Cisco IOS XE Software could allow an unauthenticated, remote attacker to cause an affected device to reload, resulting in a denial of service (DoS) condition. The vulnerability is due to improper handling of crafted TACACS+ response packets by the affected software. An attacker could exploit this vulnerability by injecting a crafted TACACS+ packet into an existing TACACS+ session between an affected device and a TACACS+ server or by impersonating a known, valid TACACS+ server and sending a crafted TACACS+ packet to an affected device when establishing a connection to the device. To exploit this vulnerability by using either method, the attacker must know the shared TACACS+ secret and the crafted packet must be sent in response to a TACACS+ request from a TACACS+ client. A successful exploit could allow the attacker to cause the affected device to reload, resulting in a DoS condition.
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Analysis
by VulDB Data Team • 03/30/2020
The vulnerability identified as CVE-2018-15369 represents a critical denial of service weakness within Cisco's network infrastructure software, specifically affecting the TACACS+ client subsystem in both IOS and IOS XE operating systems. This flaw manifests as a result of inadequate packet processing mechanisms when handling specially crafted TACACS+ response messages, creating an exploitable condition that can be leveraged by remote attackers without authentication requirements. The vulnerability exists within the authentication and authorization framework that governs network device access control, making it particularly dangerous as it can disrupt network operations and compromise the availability of critical infrastructure components.
The technical implementation of this vulnerability stems from improper input validation and memory handling within the TACACS+ client processing code. When an affected device receives a malformed TACACS+ packet containing crafted data structures, the software fails to properly validate or sanitize the incoming response before processing it. This inadequate error handling causes the system to crash and subsequently reload, effectively creating a denial of service condition. The vulnerability requires that an attacker possess knowledge of the shared TACACS+ secret to execute a successful attack, as this secret is necessary to craft legitimate-looking packets that can bypass basic authentication checks. The attack vector can be executed through two primary methods: either by injecting malicious packets into an active TACACS+ session or by impersonating a legitimate TACACS+ server during initial connection establishment.
The operational impact of CVE-2018-15369 extends beyond simple service disruption, as it can severely compromise network availability and potentially impact business continuity operations. Network administrators responsible for maintaining authentication infrastructure face significant risks when devices are vulnerable to this condition, as unauthorized actors can cause unexpected device reboots that may go unnoticed for extended periods. The DoS condition affects the entire network infrastructure that relies on TACACS+ for authentication, potentially causing cascading failures throughout connected systems. Organizations with extensive network deployments may experience service degradation or complete outages, particularly in environments where multiple devices are configured to use TACACS+ authentication. The vulnerability affects Cisco devices running IOS version 12.2 through 15.2 and IOS XE software versions 3.3 through 16.6, creating a widespread exposure across numerous network installations.
Mitigation strategies for this vulnerability should prioritize immediate patch application through official Cisco security advisories, as the company released software updates specifically addressing the TACACS+ client processing flaws. Network administrators should implement network segmentation and access control measures to limit potential attack vectors, particularly by restricting TACACS+ communication to trusted network segments. Monitoring and logging capabilities should be enhanced to detect unusual TACACS+ packet patterns or unexpected device reboots that may indicate exploitation attempts. The implementation of network access control lists and firewall rules can help prevent unauthorized TACACS+ communication from external sources, reducing the attack surface. Additionally, organizations should consider implementing redundant authentication mechanisms and establishing incident response procedures that can quickly identify and isolate affected devices during exploitation attempts, aligning with industry best practices outlined in the NIST Cybersecurity Framework and following ATT&CK framework techniques for network service disruption and credential compromise.