CVE-2026-55446: Langflow Unauthenticated Denial of Service via Malformed File Upload

Technical summary

CVE-2026-55446 is a resource exhaustion vulnerability (CWE-400) affecting Langflow's /api/v1/files/upload/ endpoint. The flaw allows unauthenticated attackers to send HTTP POST requests with abnormally long multipart form boundaries in the Content-Type header. This triggers inefficient parsing or buffer handling within the application, exhausting system resources and rendering the service unavailable. The vulnerability requires no special privileges, no user interaction, and is trivial to trigger over the network.

Business impact

This vulnerability enables attackers to launch denial-of-service attacks against Langflow deployments with minimal effort. Organizations relying on Langflow for AI workflow orchestration face service disruption, operational downtime, and potential SLA violations. The unauthenticated nature means attackers do not need insider access or compromised credentials. In production environments supporting critical automation tasks, repeated attacks could severely degrade business continuity.

Affected systems

Langflow versions prior to 1.0.19 are affected. The vulnerability is resolved in version 1.0.19 and later. Both self-hosted and cloud-hosted Langflow instances are at risk if running vulnerable versions.

Exploitability

This vulnerability has high exploitability. The attack requires only network access to the affected endpoint and can be executed by any unauthenticated user. No sophisticated tools, credentials, or user interaction are required. An attacker can trivially automate repeated requests to maintain service degradation. The low complexity and public nature of REST APIs make this a practical attack vector.

Remediation

Upgrade Langflow to version 1.0.19 or later to patch this vulnerability. Organizations should prioritize this upgrade to eliminate the unauthenticated DoS exposure. Verify the upgrade is successful by testing file upload functionality post-deployment.

Patch guidance

Apply the upgrade to Langflow 1.0.19 or later according to your deployment method (container, package manager, or manual installation). Review the official Langflow release notes for version 1.0.19 to confirm this fix is included and to identify any breaking changes or migration steps. Test uploads in a staging environment before production deployment.

Detection guidance

Monitor for unusual patterns of requests to /api/v1/files/upload/ from unexpected sources or at high frequency. Log and alert on requests with abnormally long Content-Type headers or malformed multipart boundaries. Network intrusion detection systems (IDS) may identify such requests through payload analysis. If you suspect active exploitation, check application logs for failed or hung upload requests coinciding with service degradation.

Why prioritize this

This vulnerability merits immediate attention despite not being on the KEV catalog. The combination of unauthenticated access, network reachability, trivial exploitability, and severe impact (complete service unavailability) creates a high-priority risk. Organizations should treat this as urgent if they operate Langflow in production or expose it to untrusted networks.

Risk score, explained

The CVSS 3.1 score of 7.5 (HIGH) reflects the severity of the impact: availability is completely compromised (A:H), the attack is network-based (AV:N), requires no authentication (PR:N), and no user interaction (UI:N). The score appropriately captures the serious operational risk, though the lack of confidentiality or integrity impact prevents a critical rating.

Frequently asked questions