CVE-2000-1184 in FreeBSD
Summary
by MITRE
telnetd in FreeBSD 4.2 and earlier, and possibly other operating systems, allows remote attackers to cause a denial of service by specifying an arbitrary large file in the TERMCAP environmental variable, which consumes resources as the server processes the file.
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Analysis
by VulDB Data Team • 07/21/2019
The vulnerability described in CVE-2000-1184 represents a classic denial of service flaw affecting telnetd implementations in FreeBSD versions 4.2 and earlier, with potential prevalence across other operating systems. This issue resides in the terminal capability handling mechanism of the telnet daemon, specifically when processing the TERMCAP environment variable. The vulnerability stems from insufficient input validation and resource management within the telnetd service, creating a scenario where maliciously crafted input can trigger excessive resource consumption.
The technical flaw manifests when a remote attacker manipulates the TERMCAP environment variable to specify an arbitrarily large file size or malformed terminal description data. The telnetd service processes this variable without adequate bounds checking, leading to resource exhaustion as the server attempts to parse and handle the oversized terminal capability data. This processing behavior creates a resource consumption attack vector where the system's memory and CPU resources are gradually depleted until the service becomes unresponsive or crashes entirely. The vulnerability operates at the application layer and requires no authentication to exploit, making it particularly dangerous in networked environments.
The operational impact of this vulnerability extends beyond simple service disruption, potentially affecting system availability and network reliability. When exploited successfully, the denial of service condition can render telnet services inaccessible to legitimate users while consuming significant system resources. The attack can be executed remotely without requiring any prior access credentials, making it a particularly attractive vector for attackers seeking to disrupt network services. This vulnerability directly impacts the availability aspect of the CIA triad and can be classified under CWE-400 as an Uncontrolled Resource Consumption vulnerability.
From an adversarial perspective, this vulnerability aligns with ATT&CK technique T1499.004 for Network Denial of Service and T1566.001 for Phishing. The attack chain typically involves initial reconnaissance to identify vulnerable systems, followed by exploitation through crafted TERMCAP values that trigger resource exhaustion. The vulnerability's impact is amplified by the widespread use of telnet services in network infrastructure, making it a potentially high-impact issue for network administrators and system operators. Organizations with telnet services enabled on affected systems face significant risk of service disruption and potential escalation to broader network availability issues.
Mitigation strategies for this vulnerability include immediate patching of affected FreeBSD systems to versions containing the necessary security fixes, implementing proper input validation for environment variables, and disabling unnecessary telnet services where possible. System administrators should also consider implementing resource monitoring and limiting process resource consumption through system limits. Additionally, network segmentation and firewall rules can help restrict access to telnet services, while alternative secure shell protocols should be implemented to replace telnet functionality. The vulnerability underscores the importance of proper input validation and resource management in network services, as well as the critical need for timely security patching across all system components.