CVE-2026-18899: Langflow Path Traversal Vulnerability

CVE-2026-18899 Overview

CVE-2026-18899 is a path traversal vulnerability affecting IBM Langflow OSS versions 1.0.0 through 1.11.1. A remote, unauthenticated attacker can read arbitrary files from the underlying host by manipulating file path inputs processed by the application. The flaw is classified under CWE-22: Improper Limitation of a Pathname to a Restricted Directory. Langflow is a widely adopted low-code framework for building agentic and retrieval-augmented generation (RAG) workflows on top of large language models, so exposed instances commonly hold API keys, model credentials, and connector secrets.

Critical Impact
Unauthenticated remote attackers can read sensitive files, including configuration data, credentials, and source code, from vulnerable Langflow deployments.

Affected Products

Langflow OSS 1.0.0 through 1.11.1
Deployments exposing the Langflow HTTP interface to untrusted networks
Self-hosted and containerized Langflow instances shipped inside IBM AI tooling stacks

Discovery Timeline

2026-08-28 - CVE-2026-18899 published to the National Vulnerability Database
2026-09-01 - Last updated in NVD database

Technical Details for CVE-2026-18899

Vulnerability Analysis

The vulnerability lets an attacker send crafted HTTP requests containing traversal sequences to retrieve files outside the intended directory. Because Langflow runs with the privileges of its service account, any file readable by that account is reachable. In typical deployments this includes .env files, model provider tokens, database connection strings, and stored flow definitions containing embedded secrets.

Exploitation requires no authentication, no user interaction, and no elevated privileges on the target. An attacker only needs network access to the Langflow web interface or API endpoint. Successful exploitation compromises confidentiality but does not directly affect integrity or availability of the service.

Root Cause

The root cause is insufficient validation of user-supplied path components before they are joined to a base directory and passed to file read operations. Traversal tokens such as ../ are not stripped or normalized, and the resolved path is not verified to remain within the intended parent directory. This pattern falls under CWE-22.

Attack Vector

The attack is delivered over the network against the Langflow HTTP API. An attacker issues a request to a file-serving or file-loading endpoint with a path parameter that contains traversal sequences pointing to sensitive locations such as /etc/passwd, ~/.aws/credentials, or the Langflow application configuration. The server resolves the path, opens the target file, and returns its contents in the response.

No verified public proof-of-concept exploit is currently referenced in the advisory. Refer to the IBM Support Page for vendor-provided remediation details.

Detection Methods for CVE-2026-18899

Indicators of Compromise

HTTP requests to Langflow endpoints containing ../, ..%2f, %2e%2e/, or other encoded traversal sequences in path or query parameters
Access log entries showing successful 200 OK responses to requests targeting file paths outside the Langflow working directory
Outbound activity from the Langflow service account shortly after suspicious inbound requests, indicating credential reuse

Detection Strategies

Inspect web server and reverse proxy logs for traversal patterns targeting Langflow routes that accept path or filename parameters
Deploy Web Application Firewall (WAF) signatures for path traversal payloads in front of Langflow instances
Alert on Langflow process reads of files outside its installation and data directories using file integrity or endpoint telemetry

Monitoring Recommendations

Enable verbose HTTP access logging on all Langflow deployments and forward logs to a centralized analytics platform
Baseline expected file reads by the Langflow service account and alert on deviations, especially reads of /etc/, home directories, and cloud credential files
Monitor for unauthenticated access to Langflow instances that should be restricted to internal networks or authenticated users

How to Mitigate CVE-2026-18899

Immediate Actions Required

Upgrade Langflow to a fixed release once available per the IBM Support Page
Restrict network access to Langflow instances using firewalls, VPNs, or an authenticating reverse proxy
Rotate any credentials, API keys, and tokens that may have been readable by the Langflow service account

Patch Information

IBM has published remediation guidance for Langflow OSS versions 1.0.0 through 1.11.1 on the IBM Support Page. Administrators should consult the advisory for the specific fixed version and apply the upgrade to all affected deployments.

Workarounds

Place Langflow behind a reverse proxy that normalizes and rejects requests containing traversal sequences before they reach the application
Run Langflow under a dedicated low-privilege user account with read access limited to its own installation and data directories
Remove sensitive files such as .env, cloud provider credential files, and SSH keys from any directory readable by the Langflow process

bash

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