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CVE-2026-55450 – Unauthenticated File Upload leading to DoS and Information Disclosure – Langflow…

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Summary

CVE-2026-55450 is a critical unauthenticated file upload vulnerability in Langflow, an open-source platform for building and deploying AI-powered agents and workflows. Unauthenticated remote attackers can upload arbitrary amounts of data to an exposed Langflow server, causing denial of service via disk space exhaustion, while also receiving the absolute filesystem path of uploaded files in server responses — an information leak that can be chained with other attack primitives. The vulnerability carries a CVSS v3.1 base score of 9.3 (Critical).

Technical details

  • Root cause: The file upload endpoint POST /api/v1/upload/{flow_id} in langflow/api/v1/endpoints.py lacked authentication enforcement, did not validate the flow_id parameter, and imposed no file size or upload volume limits. Files were written directly to the server filesystem and the resulting absolute file path was returned in the HTTP response.
  • Trigger conditions: Network access to a Langflow instance is the only prerequisite. No credentials, prior knowledge of the deployment, or user interaction are required.
  • Attack vector: Fully remote and unauthenticated — reachable over the network against any internet-exposed Langflow instance.
  • Impact (1) — Denial of Service: An attacker can repeatedly upload arbitrarily large files, exhausting available disk space and rendering the server unavailable.
  • Impact (2) — Information Disclosure: Each upload response includes the absolute filesystem path where the file was stored. This path disclosure leaks server-side directory structure and can facilitate chaining with other vulnerabilities.
  • CWEs identified: CWE-306 (Missing Authentication for Critical Function), CWE-400 (Uncontrolled Resource Consumption), CWE-200 (Exposure of Sensitive Information to an Unauthorized Actor).

Affected software

  • Langflow all versions prior to 1.9.1

Severity

  • CVSS v3.1 Base Score: 9.3 (Critical)
  • Vector String: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:N/A:H

Mitigation and recommended actions

  • Immediate — Patch: Upgrade Langflow to version 1.9.1 or later. The fix adds authentication requirements to the upload endpoint, enforces file size limits, and restricts absolute path disclosure to authenticated flow owners.
  • Network mitigation: If immediate patching is not possible, restrict network access to Langflow instances using firewall rules or reverse proxy controls so that the upload endpoint is not reachable from untrusted networks or the public internet.

IONIX Status

The IONIX research team is tracking ongoing exploitation attempts and recommends immediate patching. Potentially affected assets are outlined in this post.

References

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