CVE-2026-6596: Arbitrary File Upload in Langflow

Analysis indicates a critical security vulnerability in the Langflow orchestration framework. Specifically, the function create_upload_file lacks sufficient validation for incoming file requests, which can lead to arbitrary file upload and subsequent RCE.

Vulnerability Overview

The flaw stems from improper sanitization and validation of the file upload process within the create_upload_file function. An authenticated attacker can manipulate the request to bypass intended constraints, allowing for the placement of malicious files outside the designated upload directory.

Technical Analysis

I observed that the application does not enforce a whitelist for file extensions, nor does it sanitize the destination path, creating a path traversal vulnerability. By crafting a specific upload request, an attacker can place a file with arbitrary content on the underlying filesystem.

Caution

If the uploaded file is placed within an executable path (such as plugin or configuration directories), an attacker can achieve RCE by invoking the uploaded malicious script.

Forensic Artifacts

During the investigation, focus on the following artifacts to identify exploitation:

• Filesystem: Monitor for unexpected file creation in the Langflow uploads or temporary directories.
• Web Logs: Search for POST requests targeted at the */create_upload_file endpoint.
• Application Logs: Audit logs for file-processing failures or unusual activity associated with authenticated users.

Detection Logic

Sigma

Sigma Rule

title: Suspicious File Upload to Langflow
status: experimental
description: Detects unauthorized file uploads via Langflow create_upload_file endpoint
logsource:
    product: web_server
    category: web_access
detection:
    selection:
        cs-method: 'POST'
        cs-uri-stem: '*/create_upload_file'
    condition: selection
priority: high

KQL

KQL Query

index=web_logs
| search uri_path="*/create_upload_file"
| eval file_ext = replace(file_name, ".*\\.", "")
| where file_ext IN ("py", "sh", "bat", "php", "js")
| table _time, src_ip, uri_query, file_name
| sort -_time

Mitigation

1. Update: Immediately upgrade to the latest Langflow version containing the patch.
2. Validation: Implement rigorous server-side checks for file type, size, and destination path.
3. Environment: Utilize the principle of least privilege, restricting the service user’s write access to only the necessary directories.
4. Monitoring: Enable real-time file integrity monitoring on critical application folders.