CVE-2026-18891: Langflow Authentication Bypass Vulnerability

CVE-2026-18891 Overview

CVE-2026-18891 is an improper authentication vulnerability [CWE-287] affecting IBM Langflow OSS versions 1.0.0 through 1.11.1. Langflow is an open-source framework used to build agentic and retrieval-augmented generation (RAG) applications on top of large language models. The flaw allows a remote, unauthenticated attacker to execute arbitrary flows and access sensitive information within the application. Successful exploitation exposes flow definitions, prompts, embedded credentials, and any data processed by the affected flows. The issue requires no user interaction and is reachable over the network.

Critical Impact
Unauthenticated remote attackers can execute arbitrary Langflow flows and retrieve sensitive information from vulnerable Langflow OSS deployments.

Affected Products

IBM Langflow OSS 1.0.0 through 1.11.1
langflow:langflow component distributions
Self-hosted Langflow deployments exposed to untrusted networks

Discovery Timeline

2026-08-28 - CVE-2026-18891 published to NVD
2026-08-31 - Last updated in NVD database

Technical Details for CVE-2026-18891

Vulnerability Analysis

CVE-2026-18891 stems from improper authentication in the Langflow OSS application layer. The affected versions fail to properly enforce authentication controls on endpoints that execute flows and return flow-related data. An attacker who can reach the Langflow HTTP interface can invoke flow execution paths without presenting valid credentials.

Because Langflow is designed to orchestrate LLM pipelines, executed flows often contain API keys, vector store credentials, and system prompts. Triggering these flows without authorization allows the attacker to consume paid backend services, exfiltrate prompt content, and read data returned by connected tools or data sources.

The confidentiality impact is high because sensitive flow data and configuration can be retrieved. Integrity impact is limited to the state changes produced by executing flows, and availability is not directly affected.

Root Cause

The root cause is a missing or incorrectly applied authentication check on network-accessible endpoints. Requests that should require a valid session or API token are processed as if the caller were authorized. This maps to CWE-287 (Improper Authentication).

Attack Vector

The attack vector is network-based and requires no privileges or user interaction. An attacker sends crafted HTTP requests to a reachable Langflow instance targeting flow execution and data endpoints. Any Langflow OSS deployment exposed to the internet or to a broad internal network segment is directly reachable by potential attackers. See the IBM Support advisory for vendor-specific details.

Detection Methods for CVE-2026-18891

Indicators of Compromise

Unauthenticated HTTP requests to Langflow flow execution endpoints returning HTTP 200 responses.
Outbound calls from Langflow hosts to LLM providers or third-party APIs that do not correlate with authenticated user sessions.
Unexpected access to flow definitions, environment variables, or vector store data in Langflow logs.
Spikes in flow execution volume from a small set of source IP addresses.

Detection Strategies

Inspect Langflow application logs for flow execution events lacking an associated authenticated user or API key identifier.
Correlate reverse proxy access logs against authentication logs to surface flow API calls that bypass session validation.
Alert on requests to Langflow endpoints from source IPs outside expected administrative ranges.

Monitoring Recommendations

Enable verbose audit logging on Langflow and forward events to a centralized logging platform for retention and analysis.
Monitor egress traffic from Langflow servers for anomalous LLM API usage and cost spikes.
Track configuration and flow definition reads as high-value security events.

How to Mitigate CVE-2026-18891

Immediate Actions Required

Upgrade Langflow OSS to a fixed version beyond 1.11.1 as directed in the IBM Support advisory.
Remove direct internet exposure of Langflow instances and place them behind an authenticating reverse proxy or VPN.
Rotate any API keys, tokens, and credentials that were stored in flows on affected instances.
Audit flow execution logs for unauthorized invocations prior to patching.

Patch Information

Refer to the vendor advisory at IBM Support Node 7284579 for fixed version details and upgrade instructions. Apply the vendor-supplied update to a version later than 1.11.1 to remediate the improper authentication condition.

Workarounds

Restrict network access to Langflow using firewall rules or security groups so that only trusted administrators can reach the service.
Enforce authentication at an upstream reverse proxy such as nginx or a service mesh sidecar until the patch is deployed.
Disable or remove unused flows that reference sensitive credentials to limit blast radius.
Bind the Langflow service to 127.0.0.1 when remote access is not required.

bash

# Configuration example: restrict Langflow to localhost and require upstream auth
export LANGFLOW_HOST=127.0.0.1
export LANGFLOW_PORT=7860

# Example nginx snippet enforcing basic auth in front of Langflow
# location / {
#     auth_basic "Langflow";
#     auth_basic_user_file /etc/nginx/.htpasswd;
#     proxy_pass http://127.0.0.1:7860;
# }