CVE-2025-20160 in IOS
Summary
by MITRE • 09/24/2025
A vulnerability in the implementation of the TACACS+ protocol in Cisco IOS Software and Cisco IOS XE Software could allow an unauthenticated, remote attacker to view sensitive data or bypass authentication.
This vulnerability exists because the system does not properly check whether the required TACACS+ shared secret is configured. A machine-in-the-middle attacker could exploit this vulnerability by intercepting and reading unencrypted TACACS+ messages or impersonating the TACACS+ server and falsely accepting arbitrary authentication requests. A successful exploit could allow the attacker to view sensitive information in a TACACS+ message or bypass authentication and gain access to the affected device.
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Analysis
by VulDB Data Team • 07/08/2026
The vulnerability described in CVE-2025-20160 represents a critical weakness in the TACACS+ protocol implementation within Cisco IOS and IOS XE software versions. This flaw stems from insufficient validation of the required TACACS+ shared secret configuration, creating an exploitable condition that affects network device security. The vulnerability manifests when the system fails to properly verify the presence and correctness of the shared secret required for TACACS+ communication, leaving devices susceptible to unauthorized access attempts. The weakness exists at the protocol level where authentication and authorization mechanisms should enforce strict secret validation before processing any TACACS+ messages. This represents a fundamental breakdown in the security architecture that undermines the integrity of the TACACS+ authentication framework.
The technical exploitation of this vulnerability enables attackers to perform man-in-the-middle operations against TACACS+ communications without requiring authentication credentials. An attacker positioned between the network device and the TACACS+ server can intercept unencrypted TACACS+ messages and extract sensitive information including usernames, passwords, and authentication tokens. Additionally, the vulnerability allows for impersonation attacks where malicious actors can masquerade as legitimate TACACS+ servers and accept forged authentication requests. The lack of proper shared secret verification creates multiple attack vectors including credential theft, unauthorized device access, and potential privilege escalation. The vulnerability specifically impacts the authentication process where TACACS+ messages are processed, making it possible for attackers to bypass the entire authentication mechanism entirely.
The operational impact of CVE-2025-20160 extends beyond simple credential theft to encompass complete device compromise and network infiltration. Organizations relying on TACACS+ for network device authentication face significant risk as attackers can gain unauthorized access to critical network infrastructure without proper authentication. The vulnerability affects the confidentiality, integrity, and availability of network operations since sensitive authentication data becomes accessible to unauthorized parties. Network administrators may experience unauthorized access to network devices, potentially leading to data breaches, service disruption, and unauthorized network modifications. The vulnerability's remote nature means that attackers can exploit it from external network positions without requiring physical access to the affected devices, significantly expanding the attack surface and reducing the effectiveness of traditional perimeter security measures.
Security mitigations for this vulnerability should focus on implementing proper shared secret configuration and network segmentation. Organizations must ensure that all TACACS+ servers and network devices have properly configured shared secrets and that these secrets are regularly rotated. Network segmentation strategies should be implemented to isolate TACACS+ communications and prevent man-in-the-middle attacks through the use of encrypted communication channels. Cisco recommends enabling TACACS+ encryption and implementing proper network access controls to prevent unauthorized interception of authentication messages. The vulnerability aligns with CWE-312 (Sensitive Data Exposure) and CWE-287 (Improper Authentication) categories, representing weaknesses in data protection and authentication mechanisms. From an ATT&CK framework perspective, this vulnerability maps to T1078 (Valid Accounts) and T1566 (Phishing) techniques, as attackers can leverage stolen credentials or impersonate legitimate authentication servers to gain unauthorized access to network devices. Organizations should also implement network monitoring solutions to detect unusual TACACS+ traffic patterns and potential exploitation attempts.