CVE-2000-0991 in HyperTerminal
Summary
by MITRE
Buffer overflow in Hilgraeve, Inc. HyperTerminal client on Windows 98, ME, and 2000 allows remote attackers to execute arbitrary commands via a long telnet URL, aka the "HyperTerminal Buffer Overflow" vulnerability.
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Analysis
by VulDB Data Team • 02/03/2025
The CVE-2000-0991 vulnerability represents a critical buffer overflow flaw in Hilgraeve Inc.'s HyperTerminal client software, which was widely deployed on Windows 98, ME, and 2000 operating systems. This vulnerability specifically targets the client-side implementation of telnet URL handling within the HyperTerminal application, creating a pathway for remote code execution attacks. The flaw stems from inadequate input validation and bounds checking when processing excessively long telnet URLs, allowing attackers to craft maliciously formatted URLs that trigger memory corruption in the application's buffer management routines.
The technical exploitation of this vulnerability occurs when a user opens a specially crafted telnet URL through HyperTerminal, which then processes the URL without proper bounds checking. This allows an attacker to overwrite adjacent memory locations in the application's process space, potentially leading to arbitrary code execution with the privileges of the user running HyperTerminal. The vulnerability is classified as a classic stack-based buffer overflow according to CWE-121, where the buffer overflow occurs in the stack memory region, making it particularly susceptible to exploitation through carefully crafted input data.
From an operational perspective, this vulnerability poses significant risks to enterprise networks and individual users alike, as HyperTerminal was commonly used for remote system administration and terminal emulation tasks. The attack vector is particularly concerning because it can be delivered through web-based content or email attachments, making it difficult to prevent through traditional network security measures. The impact extends beyond simple privilege escalation to potentially allow attackers to gain full control over affected systems, establish persistent access, and conduct further reconnaissance activities within the network. This aligns with ATT&CK technique T1203, which covers the exploitation of software vulnerabilities for privilege escalation and system compromise.
The exploitation of this vulnerability demonstrates the importance of proper input validation and memory safety practices in client-side applications. Organizations running affected versions of HyperTerminal should immediately implement patches from the vendor or apply alternative mitigations such as disabling telnet URL handling, restricting user permissions, or implementing network segmentation to limit potential attack surface. The vulnerability also highlights the broader security challenges associated with legacy software and the need for continuous security assessments of widely deployed applications. According to industry best practices, this vulnerability should be addressed through immediate patch management, user education regarding dangerous URL handling, and implementation of network monitoring to detect potential exploitation attempts. The incident underscores the critical nature of maintaining up-to-date security patches and the potential for legacy applications to remain vulnerable to exploitation even years after their initial release.