CVE-2025-59835 in LangBot
Summary
by MITRE • 10/02/2025
LangBot is a global IM bot platform designed for LLMs. In versions 4.1.0 up to but not including 4.3.5, authorized attackers can exploit the /api/v1/files/documents interface to perform arbitrary file uploads. Since this interface does not strictly restrict the storage directory of files on the server, it is possible to upload dangerous files to specific system directories. This is fixed in version 4.3.5.
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Analysis
by VulDB Data Team • 10/03/2025
The vulnerability identified as CVE-2025-59835 affects LangBot, a global instant messaging platform specifically designed for large language models. This security flaw exists in versions 4.1.0 through 4.3.4, creating a critical pathway for unauthorized file manipulation within the system's file management infrastructure. The vulnerability manifests through the /api/v1/files/documents endpoint, which lacks proper validation mechanisms to control where uploaded files are stored within the server's file system architecture.
The technical implementation of this flaw stems from insufficient input validation and directory path restriction controls within the file upload interface. Authorized attackers who can access this specific API endpoint can manipulate the file storage location by crafting malicious requests that bypass normal directory boundaries. This allows them to upload potentially harmful files to system-critical directories such as web root directories, configuration folders, or execution paths that could lead to privilege escalation or remote code execution. The vulnerability directly maps to CWE-434, which describes insecure file upload vulnerabilities where applications fail to restrict file storage locations and types, and aligns with ATT&CK technique T1195.001 for the initial access phase through compromised credentials or API exploitation.
The operational impact of this vulnerability extends beyond simple unauthorized file uploads, as it creates a potential attack vector for more sophisticated exploitation techniques. Attackers can leverage this flaw to deploy malicious scripts, backdoors, or other harmful payloads that persist within the system's file structure. The vulnerability's severity is amplified because it affects the core file management functionality of the platform, potentially compromising the entire LLM ecosystem that relies on LangBot for communication and data exchange. Organizations using affected versions face risks including data exfiltration, system compromise, and disruption of legitimate services that depend on the platform's messaging capabilities.
The remediation for this vulnerability requires immediate deployment of version 4.3.5, which implements proper directory restriction controls and validates file storage paths to prevent unauthorized access to critical system directories. Security teams should conduct comprehensive audits of the file upload functionality to ensure all input validation mechanisms are properly enforced. Additionally, implementing network-based restrictions to limit access to the vulnerable API endpoint, combined with proper logging and monitoring of file upload activities, provides additional defense-in-depth measures. Organizations should also review their access control policies to ensure only authorized personnel can access the file management interfaces and consider implementing mandatory file type validation and content scanning to prevent malicious files from being successfully uploaded even if path restrictions are bypassed.