CVE-2025-59835 Overview
CVE-2025-59835 affects LangBot, a global instant messaging (IM) bot platform built for Large Language Models (LLMs). The vulnerability exists in the /api/v1/files/documents endpoint, which fails to restrict the storage directory of uploaded files on the server. Authenticated attackers can upload arbitrary files to specific system directories, including locations that may permit code execution or configuration tampering. The flaw is tracked as a path traversal weakness ([CWE-23]) and affects LangBot versions 4.1.0 through 4.3.4. Version 4.3.5 contains the fix.
Critical Impact
Authenticated attackers can upload dangerous files to arbitrary server directories, leading to potential remote code execution and integrity compromise across the LangBot host.
Affected Products
- LangBot versions 4.1.0 through 4.3.4
- LangBot self-hosted deployments using the documents upload API
- Any LangBot instance exposing /api/v1/files/documents to authenticated users
Discovery Timeline
- 2025-10-02 - CVE-2025-59835 published to NVD
- 2026-06-17 - Last updated in NVD database
Technical Details for CVE-2025-59835
Vulnerability Analysis
LangBot exposes a documents upload endpoint at /api/v1/files/documents to authenticated users. The handler accepts file uploads but does not enforce a constrained storage directory or sanitize file path components supplied by the client. Attackers with valid credentials can manipulate the upload request to place files outside the intended documents folder. Because LangBot integrates with LLM workflows and runs as a long-lived service, planted files can be executed or loaded by adjacent components on the host.
Root Cause
The root cause is improper limitation of a pathname to a restricted directory, classified under [CWE-23] (Relative Path Traversal). The upload handler trusts attacker-controlled filename or path metadata when constructing the destination path on disk. Without canonicalization or directory allow-listing, traversal sequences resolve to locations outside the intended upload root.
Attack Vector
Exploitation requires network access to the LangBot API and a valid low-privilege account. The attacker sends a crafted multipart upload request to /api/v1/files/documents containing path traversal segments in the filename or path field. The server writes the file to the attacker-chosen directory. Depending on where the file lands, follow-on actions include overwriting plugin scripts, dropping web-accessible payloads, or replacing configuration files consumed by the bot runtime.
No verified public proof-of-concept code is available. Refer to the LangBot Security Advisory GHSA-7j3j-qj83-9qv4 and the upstream patch pull request for implementation details.
Detection Methods for CVE-2025-59835
Indicators of Compromise
- Unexpected files written outside the LangBot documents directory, especially in plugin, configuration, or web-served paths
- HTTP requests to /api/v1/files/documents containing ../ sequences or absolute paths in filename fields
- New or modified executable scripts, .py plugin files, or YAML configuration files with recent timestamps under the LangBot install root
Detection Strategies
- Inspect application and reverse-proxy access logs for POST requests to /api/v1/files/documents with suspicious filename parameters
- Hash and compare files in LangBot plugin and configuration directories against a known-good baseline
- Alert on filesystem write events outside the designated uploads directory performed by the LangBot service account
Monitoring Recommendations
- Enable verbose request logging on the LangBot API and forward logs to a centralized analytics platform for retrospective hunting
- Monitor process executions spawned by the LangBot runtime for unexpected interpreters or shell invocations
- Track outbound network connections from the LangBot host that could indicate post-upload command-and-control activity
How to Mitigate CVE-2025-59835
Immediate Actions Required
- Upgrade LangBot to version 4.3.5 or later, which restricts the upload destination directory
- Rotate API tokens and user credentials that may have been exposed during the vulnerable window
- Audit the LangBot install directory for files written since the deployment of any version between 4.1.0 and 4.3.4
Patch Information
The maintainers fixed the issue in LangBot 4.3.5. The remediation enforces a fixed storage directory for documents uploaded through /api/v1/files/documents and rejects path components that escape this directory. See the LangBot 4.3.5 release notes and the merged patch for the code changes.
Workarounds
- Restrict network exposure of the LangBot API to trusted administrators until patching is complete
- Run LangBot under a dedicated low-privilege user account with write access limited to the uploads directory using filesystem ACLs
- Place a reverse proxy or web application firewall in front of LangBot to block requests to /api/v1/files/documents containing path traversal patterns
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
