CVE-2026-19875: IBM Langflow Auth Bypass Vulnerability

CVE-2026-19875 Overview

CVE-2026-19875 is a missing authentication vulnerability [CWE-306] affecting IBM Langflow OSS versions 1.0.0 through 1.10.0. The registration endpoint lacks authentication controls, allowing a remote unauthenticated attacker to overwrite administrator email information. Attackers can also abuse the server as an outbound email relay. IBM has published guidance on its support portal for affected customers.

Critical Impact
Remote unauthenticated attackers can overwrite administrator email information and use vulnerable Langflow instances as outbound relays, enabling account takeover paths and abuse of trusted infrastructure for spam or phishing distribution.

Affected Products

IBM Langflow OSS 1.0.0
IBM Langflow OSS versions 1.0.0 through 1.10.0
IBM Langflow OSS 1.10.0

Discovery Timeline

2026-08-19 - CVE-2026-19875 published to NVD
2026-08-20 - Last updated in NVD database

Technical Details for CVE-2026-19875

Vulnerability Analysis

CVE-2026-19875 stems from a missing authentication check on the Langflow registration endpoint. Registration functionality is exposed without requiring credentials or an authenticated session. A remote attacker can invoke the endpoint over the network with low complexity and no user interaction. The flaw impacts data integrity by permitting unauthorized modification of administrator contact information.

Overwriting the administrator email creates a direct path to account takeover. Password reset or account recovery flows tied to the administrator email can be redirected to attacker-controlled inboxes. The second impact vector is outbound relay abuse. The server's email transmission functionality can be triggered to send arbitrary messages, allowing adversaries to leverage the deployment's trusted sender reputation for phishing or spam campaigns.

Root Cause

The root cause is an authentication control missing from the registration endpoint. The application accepts registration requests without validating the caller's identity or authorization to modify administrator-scoped fields. This maps to CWE-306, Missing Authentication for Critical Function.

Attack Vector

The attack vector is network-based. An attacker sends a crafted HTTP request directly to the exposed registration endpoint of a vulnerable Langflow instance. No prior privileges, credentials, or user interaction are required. Refer to the IBM Support Page for endpoint specifics and vendor-published technical details.

Detection Methods for CVE-2026-19875

Indicators of Compromise

Unexpected changes to the administrator email address in Langflow configuration or user records without corresponding administrative activity.
Outbound SMTP traffic or email send events from the Langflow host to recipient domains unrelated to normal business communication.
HTTP POST or PUT requests to the Langflow registration endpoint originating from external or untrusted source IP addresses.
Password reset or account recovery emails delivered to unknown external addresses.

Detection Strategies

Inspect Langflow application logs for registration endpoint requests that do not correlate with an authenticated administrative session.
Baseline outbound email volume from Langflow servers and alert on deviations, particularly bursts of messages to external domains.
Monitor identity and configuration stores for unauthorized changes to the administrator email attribute.

Monitoring Recommendations

Forward Langflow web server, application, and mail relay logs to a centralized analytics platform for correlation.
Add a specific detection for HTTP requests to the registration endpoint that lack a valid session token or authentication header.
Alert on any administrator profile mutation events and require out-of-band verification before treating them as legitimate.

How to Mitigate CVE-2026-19875

Immediate Actions Required

Restrict network access to Langflow management and registration endpoints using firewall rules, reverse proxy allowlists, or VPN-only exposure until patched.
Audit the current administrator email address on every Langflow deployment in the 1.0.0 through 1.10.0 range and restore correct values where tampering is suspected.
Rotate administrator credentials and invalidate active sessions on any instance where unauthorized registration activity is observed.
Review outbound mail logs for evidence of relay abuse and notify recipients if malicious messages were sent.

Patch Information

IBM has published remediation guidance on its support portal. Review the IBM Support Page for the fixed version of IBM Langflow OSS and vendor-recommended upgrade steps. Apply the vendor-supplied update to any deployment running versions 1.0.0 through 1.10.0.

Workarounds

Place Langflow behind an authenticating reverse proxy that enforces identity checks before requests reach the registration endpoint.
Disable or firewall the registration endpoint entirely in environments that do not require self-service account creation.
Restrict outbound SMTP from the Langflow host to only approved mail infrastructure and required recipient domains.
Monitor for and manually approve any administrator email changes until the patch is deployed.

bash

# Configuration example
# Example nginx snippet to block unauthenticated access to the registration endpoint
# Adjust the location path to match your Langflow deployment
location /api/v1/register {
    allow 10.0.0.0/8;
    deny all;
    auth_basic "Restricted";
    auth_basic_user_file /etc/nginx/.htpasswd;
    proxy_pass http://langflow_backend;
}