IBM Langflow OSS Authentication Brute-Force Vulnerability (Missing Rate Limiting)

Technical Analysis

The vulnerability stems from improper restriction of excessive authentication attempts in Langflow's login mechanism, meaning no lockout, throttling, or CAPTCHA prevents repeated password guessing. An attacker with network access to the Langflow instance can script automated credential-stuffing or brute-force attacks against exposed login endpoints. Successful compromise grants the attacker the victim's full account privileges within Langflow, including access to configured agent flows, API keys, connected data sources, and any downstream tools or MCP-style integrations orchestrated through the platform. Because Langflow is often used as an orchestration layer for LLM agents, an account takeover here can cascade into unauthorized modification of agent behavior, exfiltration of embedded secrets, or injection of malicious flows/tools that execute in the context of legitimate users.

Affected Systems

Langflow (IBM Langflow OSS, versions 1.0.0 through 1.9.6)

Detection Signatures

• High-frequency login attempts from single IP/user-agent against /api/v1/login or equivalent auth endpoints
• Spikes in HTTP 401/403 responses without corresponding account lockout events
• Absence of increasing response delay or CAPTCHA challenge after repeated failed logins
• Multiple failed authentication attempts across short time windows in Langflow server logs
• Unusual successful login following a burst of failures (indicator of successful brute-force)

Remediation Steps

1. 1

   Upgrade Langflow

   Update to a patched Langflow release beyond 1.9.6 once IBM issues a fix, or apply any available official patch/hotfix for CVE-2026-19297.

2. 2

   Implement rate limiting

   Deploy a reverse proxy or WAF in front of Langflow to enforce request throttling and IP-based rate limiting on authentication endpoints.

3. 3

   Enable account lockout / backoff

   Configure or add account lockout policies, exponential backoff, or CAPTCHA after a small number of failed login attempts.

4. 4

   Enforce MFA

   Require multi-factor authentication for all Langflow user accounts to reduce impact of credential compromise.

5. 5

   Monitor authentication logs

   Set up alerting for abnormal login attempt volumes and integrate Langflow auth logs with SIEM for real-time detection.

6. 6

   Restrict network exposure

   Limit Langflow instance access to trusted networks/VPN rather than exposing login interfaces directly to the internet.