CVE-2018-1083 in zsh
Summary
by MITRE
Zsh before version 5.4.2-test-1 is vulnerable to a buffer overflow in the shell autocomplete functionality. A local unprivileged user can create a specially crafted directory path which leads to code execution in the context of the user who tries to use autocomplete to traverse the before mentioned path. If the user affected is privileged, this leads to privilege escalation.
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Analysis
by VulDB Data Team • 02/24/2023
The vulnerability identified as CVE-2018-1083 represents a critical buffer overflow flaw within the zsh shell's autocomplete functionality that affects versions prior to 5.4.2-test-1. This issue stems from inadequate input validation and memory management within the shell's tab completion system, which is designed to assist users in navigating file system paths and executing commands more efficiently. The vulnerability specifically manifests when the shell processes directory paths that contain maliciously crafted input, creating a condition where buffer boundaries are exceeded during the autocomplete operation.
The technical exploitation of this vulnerability occurs through a carefully constructed directory path that triggers the buffer overflow during autocomplete processing. When an unprivileged user creates such a path and another user attempts to navigate through it using zsh's tab completion feature, the shell's memory handling fails to properly bound the buffer allocation, leading to memory corruption that can be leveraged for arbitrary code execution. This flaw operates at the kernel level of shell functionality, where the autocomplete mechanism does not properly sanitize user-provided input before processing it within the shell's internal buffers. The vulnerability is classified under CWE-121 as a stack-based buffer overflow, which occurs when a program writes more data to a buffer than it can hold, potentially overwriting adjacent memory locations including return addresses and function pointers.
The operational impact of CVE-2018-1083 extends beyond simple local privilege escalation to represent a sophisticated attack vector that can be weaponized in various security contexts. When an unprivileged user crafts a malicious directory structure, they can potentially execute code with the privileges of any user who subsequently uses autocomplete to traverse that path. This creates a persistent threat vector where attackers can establish footholds on systems by simply creating specific directory names that contain malicious input patterns. The vulnerability is particularly concerning in multi-user environments where users may have different privilege levels, as it allows for privilege escalation from lower to higher user accounts. Additionally, the vulnerability can be exploited in conjunction with other attack techniques to create more complex attack chains, potentially leading to complete system compromise.
Mitigation strategies for CVE-2018-1083 require immediate patching of affected zsh installations to version 5.4.2-test-1 or later, which contains the necessary fixes for the buffer overflow condition. System administrators should also implement comprehensive monitoring of directory creation activities, particularly in areas where users have write permissions, to detect potential malicious path creation attempts. The implementation of privilege separation mechanisms and mandatory access controls can help limit the scope of potential exploitation, while regular security audits should verify that no maliciously crafted paths exist in the system. From an ATT&CK framework perspective, this vulnerability maps to techniques involving privilege escalation and defense evasion, as attackers can use it to establish persistent access and avoid detection by normal security monitoring systems. Organizations should also consider implementing input validation controls at the shell level and restricting shell access to only trusted users, while maintaining regular updates to ensure all shell components remain patched against known vulnerabilities.