CVE-2000-0476 in X11r6
Summary
by MITRE
xterm, Eterm, and rxvt allow an attacker to cause a denial of service by embedding certain escape characters which force the window to be resized.
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Analysis
by VulDB Data Team • 06/17/2025
The vulnerability identified as CVE-2000-0476 affects several terminal emulators including xterm Eterm and rxvt applications that process escape sequences for terminal control. This issue stems from the improper handling of escape characters within terminal emulators, specifically those related to window resizing operations. The flaw allows an attacker to craft malicious escape sequences that when processed by these terminal applications can trigger unintended window resizing behavior. When these applications encounter specially crafted escape sequences designed to manipulate terminal window dimensions, they fail to properly validate or sanitize the input parameters, leading to potential denial of service conditions. The vulnerability is particularly concerning because it can be exploited through simple text input or terminal output manipulation without requiring any special privileges or complex attack vectors.
The technical root cause of this vulnerability lies in the insufficient validation of escape sequence parameters within terminal emulators. When these applications receive escape sequences intended to resize windows, they do not properly verify the legitimacy of the requested dimensions or the sequence itself. This lack of input sanitization creates a condition where malformed or malicious escape sequences can cause the terminal application to enter an infinite loop or allocate excessive resources during the window resizing process. The escape sequences typically involve control codes that manipulate terminal window properties, and when these codes are improperly interpreted, they can force the terminal to continuously resize itself or consume excessive system resources. This behavior directly maps to CWE-122 which describes improper validation of buffer limits and CWE-400 which covers excessive resource consumption.
The operational impact of this vulnerability extends beyond simple denial of service conditions as it can affect system availability and user productivity. When exploited, the vulnerability can cause terminal applications to become unresponsive or consume all available system resources, effectively rendering the terminal unusable for legitimate users. This is particularly problematic in environments where terminal emulators are heavily used for system administration tasks, development work, or remote access sessions. The vulnerability can be exploited through various means including email attachments, web content, or any mechanism that allows text to be displayed within the terminal environment. The exploitation requires minimal technical knowledge and can be carried out by any attacker with basic understanding of terminal escape sequences, making it a significant concern for system administrators and security professionals. The impact is further amplified when considering that many system management tasks rely heavily on terminal applications, making this vulnerability potentially disruptive to critical system operations.
Mitigation strategies for this vulnerability should focus on input validation and proper escape sequence handling within terminal emulators. System administrators should ensure that all affected terminal applications are updated with patches that properly validate escape sequence parameters and implement reasonable limits on window resizing operations. The recommended approach involves implementing strict bounds checking on all escape sequence parameters and establishing maximum limits for window dimension changes. Additionally, organizations should consider implementing terminal application hardening measures such as disabling unnecessary escape sequence processing or implementing sandboxing techniques to limit the impact of potential exploitation. Network administrators should also consider monitoring for unusual terminal behavior or excessive resource consumption that might indicate exploitation attempts. The mitigation aligns with ATT&CK technique T1059.007 which covers terminal shell commands and T1499.004 which addresses network denial of service attacks. Regular security assessments and vulnerability scanning should be performed to ensure that terminal applications remain patched and secure against similar vulnerabilities. The remediation process should also include user education about the risks of opening untrusted terminal content and the importance of keeping terminal applications updated with the latest security patches.