CVE-2026-17621: Langflow Path Traversal Vulnerability

CVE-2026-17621 Overview

CVE-2026-17621 is a path traversal vulnerability affecting IBM Langflow OSS versions 1.0.0 through 1.10.2. A remote authenticated attacker can send a specially crafted URL containing ../ sequences to read arbitrary files on the underlying host operating system. The flaw is classified under CWE-22: Improper Limitation of a Pathname to a Restricted Directory. Langflow runs on Windows, macOS, and Linux, so the exposure crosses all supported deployment targets. IBM published a support advisory tracking remediation guidance for affected customers.

Critical Impact
Authenticated remote attackers can read arbitrary files accessible to the Langflow process, including configuration data, credentials, and application source code.

Affected Products

IBM Langflow OSS versions 1.0.0 through 1.10.2
Deployments on Apple macOS, Linux, and Microsoft Windows hosts
Any downstream service integrating the vulnerable Langflow API

Discovery Timeline

2026-09-04 - CVE-2026-17621 published to NVD
2026-09-10 - Last updated in NVD database

Technical Details for CVE-2026-17621

Vulnerability Analysis

Langflow is an open-source visual framework for building LLM-powered applications. The affected endpoints accept file path parameters over HTTP without proper canonicalization. An attacker with low-privilege access to the API can inject directory traversal sequences to escape the intended base directory. Successful exploitation exposes files that the Langflow service account can read on the host. This includes environment files containing API keys, database credentials, model configuration files, and flow definitions.

The attack requires network access and a valid low-privilege authenticated session but no user interaction. Exploitation impacts confidentiality and integrity because attackers can enumerate sensitive files and potentially manipulate flow artifacts. Availability is not directly affected.

Root Cause

The root cause is insufficient input validation on user-controlled path components. The application concatenates untrusted URL input into filesystem operations without resolving symbolic references or verifying that the final path remains within the intended directory boundary. Sequences such as /../ traverse upward in the directory tree during resolution, giving attackers access to arbitrary locations on the host filesystem.

Attack Vector

An authenticated attacker sends an HTTP request to a vulnerable Langflow endpoint with a crafted path parameter. The payload embeds ../ sequences to traverse outside the application's working directory. The server processes the request, resolves the traversed path, and returns file contents in the response. On Linux hosts, attackers commonly target /etc/passwd, /proc/self/environ, or application configuration files. On Windows, targets include configuration files under the Langflow install directory or user profile paths.

See the IBM Support advisory for vendor-supplied technical detail.

Detection Methods for CVE-2026-17621

Indicators of Compromise

HTTP request logs containing ../, ..%2f, or %2e%2e%2f sequences targeting Langflow endpoints
Responses from Langflow returning unusually large payloads or file-like content on endpoints that normally serve JSON
Access to sensitive host files such as /etc/passwd, .env, or id_rsa correlated with the Langflow service account

Detection Strategies

Deploy web application firewall rules that decode URL parameters and flag traversal patterns before they reach the Langflow process
Alert on Langflow API requests where path parameters contain .., backslashes, or URL-encoded traversal payloads
Correlate authenticated Langflow sessions with unexpected filesystem read activity on the host

Monitoring Recommendations

Enable verbose request logging on the Langflow application and forward logs to a centralized analytics platform
Monitor process-level file access telemetry for the Langflow service account to identify reads outside expected directories
Track authentication events for low-privilege Langflow accounts that generate anomalous request volumes

How to Mitigate CVE-2026-17621

Immediate Actions Required

Upgrade Langflow to a version above 1.10.2 per the IBM Support advisory
Restrict network access to Langflow API endpoints to trusted management networks only
Rotate any credentials, API keys, or tokens stored in files accessible to the Langflow service account
Audit Langflow access logs for traversal sequences dating back to the initial deployment

Patch Information

IBM has published remediation guidance in the IBM Support advisory. Administrators should apply the fixed release identified by IBM and validate that Langflow no longer accepts traversal payloads on any file-serving endpoint. Confirm the running version after upgrade and restart the service to load patched code paths.

Workarounds

Place Langflow behind a reverse proxy that normalizes URLs and rejects traversal sequences before forwarding requests
Run the Langflow process under a dedicated low-privilege user account with filesystem access restricted to required directories
Apply mandatory access controls such as AppArmor or SELinux profiles that limit which paths Langflow can read

bash

# Example nginx location block to block traversal attempts
location /api/ {
    if ($request_uri ~* "(\.\./|\.\.%2f|%2e%2e/)") {
        return 403;
    }
    proxy_pass http://langflow_backend;
}