CVE-2026-55450: Langflow: Unauthenticated file upload leads to DoS (space exhaustion) and information leak

Synopsis

An unrestricted file upload vulnerability in Langflow (the AI agent and workflow builder) allows any unauthenticated attacker reachable over the network to upload arbitrary amounts of data to the server. Successful exploitation exhausts available disk space, disrupting or crashing the service, and the server response leaks the absolute file path of each uploaded file, giving attackers a foothold for chaining further attacks. No fix version has been published yet; HarborGuard is tracking the advisory for patch availability and will surface a patched-image rebuild the moment an upstream fix is released.

HarborGuard Coverage

Exploit Conditions

• Network reachabilityRequired

  The attacker must be able to reach the Langflow service over the network; no local or physical access is required.

• AuthenticationNot required

  No credentials or prior account registration are needed; the upload endpoint is fully unauthenticated.

• Victim interactionNot required

  The attacker acts entirely on their own; no user of the target system needs to click anything or take any action.

• Attack complexityDetail

  The exploit is straightforward and condition-free: any attacker with network access can trigger it reliably without needing to satisfy race conditions or specific environmental requirements.

Blast Radius

• Floods the server's storage with attacker-controlled data, exhausting available disk space and crashing or severely degrading the Langflow service for all users.
• Receives the absolute filesystem path of every uploaded file in the server response, exposing internal directory structure that can be used to locate configuration files, secrets, or other sensitive assets for follow-on attacks.
• Repeated uploads can be automated with no rate limiting, meaning a single attacker can sustain a denial-of-service condition indefinitely until the vulnerability is mitigated.
• The path disclosure creates a concrete assist for chaining additional exploits, such as path traversal or local file inclusion attacks if other vulnerabilities exist on the same host.