CVE-2008-1142 in rxvt-unicode
Summary
by MITRE
rxvt 2.6.4 opens a terminal window on :0 if the DISPLAY environment variable is not set, which might allow local users to hijack X11 connections. NOTE: it was later reported that rxvt-unicode, mrxvt, aterm, multi-aterm, and wterm are also affected. NOTE: realistic attack scenarios require that the victim enters a command on the wrong machine.
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Analysis
by VulDB Data Team • 08/10/2019
The vulnerability identified as CVE-2008-1142 affects the rxvt terminal emulator version 2.6.4 and related terminal applications including rxvt-unicode, mrxvt, aterm, multi-aterm, and wterm. This security flaw stems from the application's improper handling of the DISPLAY environment variable, which is fundamental to X Window System operations on Unix-like systems. When the DISPLAY variable is not explicitly set, rxvt defaults to opening terminal windows on display :0, which represents the local machine's primary X server connection.
The technical nature of this vulnerability falls under CWE-200, which describes improper output handling that can lead to information exposure, and more specifically relates to CWE-284, which addresses improper access control mechanisms. The flaw creates a dangerous scenario where local users can potentially hijack X11 connections by exploiting the default behavior of these terminal emulators. When applications fail to properly validate or sanitize the DISPLAY environment variable, they inadvertently expose the system to unauthorized access attempts that could compromise the graphical user interface session.
The operational impact of this vulnerability extends beyond simple privilege escalation concerns. Attackers can leverage this weakness to gain unauthorized access to graphical sessions, potentially intercepting user input, accessing sensitive graphical applications, or performing actions that require graphical interface privileges. The attack requires a specific condition where victims must enter commands on the wrong machine, indicating that social engineering or user confusion plays a significant role in exploitation. This makes the vulnerability particularly dangerous in multi-user environments where users might accidentally execute commands on systems they don't intend to interact with, especially when they're in a hurry or working in unfamiliar environments.
The attack vector demonstrates the classic principle of security by obscurity being insufficient for protection. Even though the vulnerability requires user action to complete the attack, the default behavior of opening connections to display :0 creates an exploitable condition that can be leveraged by attackers who understand the X11 architecture. This aligns with ATT&CK technique T1068, which describes the use of local system privileges to gain access to graphical sessions. Organizations should implement proper environment variable validation and ensure that terminal emulators are configured to require explicit display specifications rather than defaulting to local connections. The vulnerability highlights the importance of secure default configurations and proper input validation in GUI applications, as it demonstrates how seemingly innocuous default behaviors can create significant security risks in multi-user environments where access control is paramount.