CVE-2014-2906 in fish
Summary
by MITRE
The psub function in fish (aka fish-shell) 1.16.0 before 2.1.1 does not properly create temporary files, which allows local users to execute arbitrary commands via a temporary file with a predictable name.
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Analysis
by VulDB Data Team • 05/15/2023
The vulnerability identified as CVE-2014-2906 affects the fish shell version 1.16.0 and earlier versions before 2.1.1, specifically within the psub function implementation. This flaw represents a critical security issue that stems from improper temporary file creation practices, creating a path for local privilege escalation through command execution. The vulnerability allows attackers to manipulate temporary files with predictable naming conventions, enabling them to execute arbitrary code with the privileges of the affected user. The psub function in fish shell is designed to handle background processes and temporary file operations, but the implementation fails to properly secure temporary file creation mechanisms.
The technical exploitation of this vulnerability relies on the predictable naming pattern of temporary files created by the psub function. When fish shell generates temporary files for process substitution operations, it uses a naming scheme that can be anticipated by local attackers. This predictability enables malicious users to create their own temporary files with the same names before the legitimate process can create them, effectively hijacking the temporary file creation process. The flaw operates at the system level where temporary files are created without proper security measures such as secure temporary file creation functions or unique naming schemes. This vulnerability directly maps to CWE-377: Insecure Temporary File and CWE-379: Creation of Temporary File With Insecure Permissions, both of which are well-documented weaknesses in software security practices.
The operational impact of this vulnerability extends beyond simple command execution, as it represents a privilege escalation vector that can be leveraged by local attackers to gain elevated system access. When a user executes commands that trigger the psub function, the attacker can potentially inject malicious code that gets executed in the context of the shell process. The vulnerability is particularly concerning because it requires no special privileges to exploit, as the attacker only needs local access to the system where fish shell is installed. This makes it a significant threat in multi-user environments where local attackers could potentially compromise other users' sessions or escalate privileges to gain system-level access. The attack surface is broad since any application or user interaction that triggers the psub function could be exploited.
Mitigation strategies for CVE-2014-2906 should focus on updating to fish shell version 2.1.1 or later, which contains the patched implementation of the psub function with proper temporary file creation mechanisms. The fix implemented in the updated versions typically involves using secure temporary file creation functions that generate unique filenames or employ proper file permissions to prevent symlink attacks. Organizations should also implement additional security measures such as restricting access to the fish shell binary, monitoring for suspicious temporary file creation patterns, and ensuring that all systems are regularly updated with the latest security patches. From an ATT&CK perspective, this vulnerability aligns with T1059.001: Command and Scripting Interpreter and T1068: Exploitation for Privilege Escalation, demonstrating how local privilege escalation can be achieved through insecure temporary file handling. System administrators should also consider implementing process monitoring to detect potential exploitation attempts and ensure that temporary file directories have appropriate permissions to prevent unauthorized file creation or modification.