CVE-2016-10714 in zsh
Summary
by MITRE
In zsh before 5.3, an off-by-one error resulted in undersized buffers that were intended to support PATH_MAX characters.
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Analysis
by VulDB Data Team • 02/16/2023
The vulnerability identified as CVE-2016-10714 represents a critical buffer overflow condition within the zsh shell implementation that existed in versions prior to 5.3. This flaw stems from an off-by-one error in the memory allocation logic that governs how the shell handles file paths and directory navigation. The issue manifests when the shell attempts to process file paths that approach the maximum allowable length defined by PATH_MAX constant, which typically represents the maximum number of bytes in a complete pathname. The buffer sizing calculation incorrectly computes the required memory allocation, resulting in buffers that are one byte smaller than the intended capacity for handling PATH_MAX characters.
The technical exploitation of this vulnerability occurs when zsh processes file paths that are near or equal to the PATH_MAX limit, causing the shell to write beyond the allocated buffer boundaries. This memory corruption can lead to unpredictable behavior including shell crashes, denial of service conditions, or potentially more severe consequences if the overflow allows for arbitrary code execution. The off-by-one error specifically affects the internal buffer management routines that handle path resolution and file operations, making it particularly dangerous in environments where zsh is used for automated scripting or when processing user-supplied file paths of varying lengths. The vulnerability's impact is amplified because zsh is widely used as a default shell on many Unix-like systems including macOS and various Linux distributions, making it a prime target for exploitation in privilege escalation scenarios.
From a cybersecurity perspective, this vulnerability aligns with CWE-121, which describes stack-based buffer overflow conditions, and demonstrates how seemingly minor mathematical errors in buffer sizing can result in significant security implications. The vulnerability operates within the ATT&CK framework under the technique of privilege escalation through software exploitation, as attackers could potentially leverage this flaw to gain elevated privileges when zsh is used in setuid contexts or when users execute shell scripts with elevated permissions. The operational impact extends beyond simple denial of service since the vulnerability could be exploited in automated attacks against systems where zsh is the default shell, particularly in enterprise environments where shell scripting is prevalent. The vulnerability's remediation requires updating to zsh version 5.3 or later, where the buffer allocation logic has been corrected to properly account for PATH_MAX requirements. Organizations should prioritize patching this vulnerability across their infrastructure, especially in environments where zsh is used for critical automation tasks or where users might be exposed to untrusted file paths. The vulnerability also highlights the importance of thorough testing of buffer management code in shell implementations and demonstrates how standard security practices such as input validation and proper memory allocation can prevent such critical flaws from persisting in widely-used software components.