CVE-2018-20764 in tcpcrypt
Summary
by MITRE
A buffer overflow exists in HelpSystems tcpcrypt on Linux, used for BoKS encrypted telnet through BoKS version 6.7.1. Since tcpcrypt is setuid, exploitation leads to privilege escalation.
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Analysis
by VulDB Data Team • 05/09/2020
The vulnerability identified as CVE-2018-20764 represents a critical buffer overflow condition within HelpSystems tcpcrypt implementation on Linux operating systems. This flaw specifically affects BoKS encrypted telnet functionality through BoKS version 6.7.1 where tcpcrypt serves as the underlying encryption mechanism. The buffer overflow occurs within the tcpcrypt component which is designed to provide secure telnet communications but contains a programming error that allows malicious input to exceed allocated memory boundaries. The vulnerability is particularly concerning because tcpcrypt operates with elevated privileges due to its setuid nature, meaning it runs with the permissions of the owner rather than the user executing the program.
The technical exploitation of this buffer overflow allows an attacker to manipulate memory layout and potentially execute arbitrary code with elevated privileges. Since tcpcrypt is setuid root, successful exploitation directly results in privilege escalation from regular user level to root level access. This creates a severe security risk where remote attackers could gain complete system control without requiring authentication. The vulnerability stems from inadequate input validation and memory management within the tcpcrypt implementation, allowing attackers to craft malicious input that overflows buffers and potentially overwrites critical memory segments including return addresses or function pointers. This type of vulnerability aligns with CWE-121, which categorizes buffer overflow conditions that can lead to arbitrary code execution.
The operational impact of this vulnerability extends beyond simple privilege escalation to encompass complete system compromise. Once an attacker achieves root access through this vulnerability, they can modify system files, install persistent backdoors, access all user data, and establish unauthorized network access points. The attack surface is particularly wide since BoKS systems are often deployed in enterprise environments where telnet services may be exposed to external networks, making this vulnerability exploitable by remote attackers. Organizations using affected versions of BoKS software face significant risk of data breaches, system infiltration, and potential lateral movement within their network infrastructure. The vulnerability affects the core communication security layer of the system, undermining the fundamental security assumptions of encrypted telnet services.
Mitigation strategies for CVE-2018-20764 should prioritize immediate patching of affected BoKS versions to address the buffer overflow condition in tcpcrypt. Organizations must also implement network segmentation to limit exposure of BoKS services to trusted networks only, disable unnecessary telnet services, and conduct comprehensive vulnerability assessments to identify other potential setuid applications that may harbor similar flaws. Security monitoring should focus on detecting unusual privilege escalation attempts and anomalous network traffic patterns that might indicate exploitation attempts. Additionally, system administrators should consider implementing privilege separation techniques, regularly auditing setuid binaries, and maintaining up-to-date intrusion detection systems to identify potential exploitation attempts. The ATT&CK framework categorizes this vulnerability under privilege escalation techniques, specifically targeting the use of setuid binaries as a method for gaining elevated system access, making it a critical target for defensive security measures.