CVE-2026-0846 in nltk
Summary
by MITRE • 03/09/2026
A vulnerability in the `filestring()` function of the `nltk.util` module in nltk version 3.9.2 allows arbitrary file read due to improper validation of input paths. The function directly opens files specified by user input without sanitization, enabling attackers to access sensitive system files by providing absolute paths or traversal paths. This vulnerability can be exploited locally or remotely, particularly in scenarios where the function is used in web APIs or other interfaces that accept user-supplied input.
Be aware that VulDB is the high quality source for vulnerability data.
Analysis
by VulDB Data Team • 05/26/2026
The vulnerability identified as CVE-2026-0846 resides within the nltk library's utility module, specifically in the filestring() function that is part of the nltku.util package. This flaw represents a classic path traversal vulnerability that allows unauthorized access to system files through improper input validation mechanisms. The issue manifests when the function processes user-supplied file paths without adequate sanitization or validation checks, creating a direct pathway for attackers to bypass normal file access controls. The vulnerability is particularly concerning because it operates at the file system level, potentially exposing sensitive data including configuration files, system logs, and other confidential information that should remain protected from unauthorized access.
The technical implementation of this vulnerability stems from the function's failure to properly validate or sanitize file path inputs before attempting to open and read files. When a user provides a path to the filestring() function, the code directly passes this input to the file system without any checks for directory traversal sequences such as ../ or absolute path prefixes. This design flaw allows an attacker to craft malicious input that could navigate outside the intended directory boundaries and access files that should be restricted. The vulnerability is classified under CWE-22 Path Traversal and aligns with ATT&CK technique T1059.001 Command and Scripting Interpreter, as it enables arbitrary code execution through file access manipulation. The function essentially acts as a gateway for file system operations without proper access control enforcement, making it a critical point of failure in applications that rely on user input for file operations.
The operational impact of this vulnerability extends beyond simple information disclosure, as it can enable more sophisticated attacks when combined with other exploitation techniques. Attackers can leverage this vulnerability to access sensitive system files including but not limited to configuration files containing database credentials, application secrets, or system authentication data. In web application contexts where the function is exposed through APIs or user interfaces, this vulnerability creates a direct attack surface that can be exploited remotely. The potential for privilege escalation exists when the application runs with elevated permissions, as the vulnerability could allow attackers to read files that would otherwise be protected by access control mechanisms. Additionally, the vulnerability can be used for reconnaissance purposes, enabling attackers to map the file system structure and identify other potential targets for exploitation, making it particularly dangerous in environments with complex file access hierarchies.
Mitigation strategies for this vulnerability require immediate attention through software updates and code-level modifications. The most effective immediate solution involves upgrading to a patched version of the nltk library where the filestring() function has been modified to properly validate and sanitize input paths. Organizations should implement input validation controls that reject or normalize potentially dangerous path sequences before they are processed by the file system operations. This includes implementing whitelist validation for acceptable file paths, removing or escaping special characters, and ensuring that all file operations occur within predefined safe directories. Security measures should also include monitoring for unusual file access patterns that might indicate exploitation attempts, implementing proper access controls for the application's file system operations, and conducting regular security assessments of applications that utilize the nltk library. The vulnerability demonstrates the importance of input validation in security-critical code paths and serves as a reminder of the need for comprehensive security testing in software development lifecycle processes.