CVE-2016-1888 in FreeBSD
Summary
by MITRE
The telnetd service in FreeBSD 9.3, 10.1, 10.2, 10.3, and 11.0 allows remote attackers to inject arguments to login and bypass authentication via vectors involving a "sequence of memory allocation failures."
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Analysis
by VulDB Data Team • 06/19/2019
The telnetd service in FreeBSD versions 9.3, 10.1, 10.2, 10.3, and 11.0 contains a critical vulnerability that enables remote attackers to bypass authentication mechanisms through a sophisticated memory allocation failure exploit. This vulnerability specifically targets the argument injection mechanism within the login process, allowing malicious actors to manipulate the authentication flow by leveraging memory allocation failures that occur during service operation. The flaw exists in the way the telnetd service handles memory allocation during the authentication sequence, creating a pathway for unauthorized access that circumvents standard security controls.
The technical implementation of this vulnerability involves a sequence of memory allocation failures that occur when the telnetd service attempts to process login arguments. When memory allocation fails during the authentication process, the service does not properly handle these failures, leading to a state where attacker-controlled arguments can be injected into the login process. This memory management flaw creates a condition where the service continues execution with corrupted or manipulated argument structures, effectively allowing remote attackers to inject arbitrary arguments that influence the authentication decision-making process. The vulnerability manifests as a failure in proper input validation and memory handling during the login sequence, which is categorized under CWE-129 and CWE-704 within the Common Weakness Enumeration framework.
The operational impact of this vulnerability is severe and far-reaching for FreeBSD systems running the affected telnetd service versions. Remote attackers can exploit this weakness to gain unauthorized access to systems without proper authentication credentials, potentially leading to complete system compromise. The vulnerability undermines fundamental security controls by allowing attackers to bypass authentication entirely, making it particularly dangerous for systems that rely on telnet for remote administration. This weakness enables privilege escalation attacks and provides a foothold for further exploitation within network environments. The attack vector involves sending specially crafted sequences to the telnet service that trigger the memory allocation failure conditions, allowing argument injection that bypasses the standard login authentication mechanisms.
Organizations should implement immediate mitigations including upgrading to patched versions of FreeBSD that address the memory allocation handling in telnetd service implementations. The recommended approach involves applying security patches that correct the argument injection handling during authentication and improve memory allocation error recovery mechanisms. System administrators should also consider disabling telnet services entirely and migrating to more secure alternatives such as ssh protocols that do not exhibit similar memory management vulnerabilities. Additional defensive measures include implementing network segmentation to limit access to telnet services and monitoring for unusual authentication patterns that might indicate exploitation attempts. The vulnerability aligns with ATT&CK technique T1075 which covers legitimate credentials usage and T1566 which involves credential access through network service exploitation, making it a significant concern for enterprise security postures.