CVE-2023-45239 in tac_plus
Summary
by MITRE • 10/25/2023
A lack of input validation exists in tac_plus prior to commit 4fdf178 which, when pre or post auth commands are enabled, allows an attacker who can control the username, rem-addr, or NAC address sent to tac_plus to inject shell commands and gain remote code execution on the tac_plus server.
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Analysis
by VulDB Data Team • 09/19/2024
The vulnerability CVE-2023-45239 represents a critical security flaw in the tac_plus authentication daemon that affects systems relying on TACACS+ protocol for remote access control. This issue stems from insufficient input validation mechanisms within the tac_plus software, specifically in versions prior to commit 4fdf178. The vulnerability becomes particularly dangerous when pre-authentication or post-authentication commands are enabled, as these features create pathways for malicious command injection attacks. The flaw allows attackers to manipulate authentication parameters including username, remote address, or NAC address fields, which are then processed by the daemon without adequate sanitization. This lack of proper input validation creates an environment where attacker-controlled data can be interpreted as executable commands rather than simple authentication parameters. The vulnerability directly maps to CWE-77 and CWE-94 in the Common Weakness Enumeration catalog, which classify it as a command injection vulnerability and a code injection flaw respectively. From an operational perspective, this vulnerability presents a severe risk to network infrastructure security as it enables remote code execution on the tac_plus server itself, potentially allowing attackers to escalate privileges, establish persistent access, or compromise the entire authentication infrastructure. The attack surface is particularly concerning because TACACS+ servers often serve as central authentication points for network device management, making them prime targets for attackers seeking to gain unauthorized access to critical network resources.
The technical exploitation of this vulnerability requires an attacker to control specific input fields that are processed by the tac_plus daemon during authentication workflows. When pre-auth or post-auth commands are configured, these commands are executed in the context of the tac_plus process, which typically runs with elevated privileges. The attacker can inject malicious shell commands through the username, rem-addr, or NAC address parameters, causing the daemon to execute unintended code on the server. This type of injection attack aligns with ATT&CK technique T1059.001 for command and scripting interpreter and T1068 for exploit for privilege escalation. The vulnerability essentially transforms the legitimate authentication process into a code execution vector, where the daemon's command processing logic fails to distinguish between legitimate authentication data and malicious command payloads. The impact extends beyond simple remote code execution as the compromised server can then be used as a pivot point for further attacks within the network infrastructure. Network administrators who have configured pre-auth or post-auth commands are particularly at risk, as these features are commonly enabled to perform additional authentication checks or device-specific configurations. The vulnerability demonstrates a classic failure in input sanitization and validation that has been addressed in subsequent commits to the tac_plus codebase, highlighting the importance of maintaining up-to-date security patches in network infrastructure components.
Organizations must implement immediate mitigations to protect against exploitation of CVE-2023-45239, starting with upgrading to versions containing commit 4fdf178 or later. Network segmentation and access controls should be strengthened around tac_plus servers to limit exposure to potentially malicious actors. The implementation of network monitoring solutions capable of detecting unusual command execution patterns or unexpected authentication parameter values can serve as an early warning system. Security teams should conduct comprehensive audits of all TACACS+ implementations to identify and disable unnecessary pre-auth or post-auth command features where possible. The vulnerability underscores the importance of principle of least privilege in network infrastructure management, where authentication daemons should operate with minimal required permissions. Additionally, implementing proper input validation at multiple layers of the authentication process can provide defense-in-depth against similar vulnerabilities. Regular security assessments of authentication infrastructure components are essential to identify potential injection points and ensure that all security patches are properly applied. The incident serves as a reminder that authentication systems, while often considered secure by design, can become attack vectors when input validation is insufficient. Organizations should also consider implementing intrusion detection systems specifically tuned to monitor for TACACS+ protocol anomalies that could indicate exploitation attempts. The vulnerability's classification under CWE-77 and its potential for privilege escalation through T1068 ATT&CK technique emphasizes the critical need for comprehensive security measures beyond simple patch management.