HTTP 400 Status Codes

Description

An application or device had an excessive number of responses with an HTTP 400-level status code, which indicates that a client issued a valid command to the device that was not successful.

Background

HTTP is a communication protocol that enables users to deliver data over the internet. An unusual increase in HTTP 400-level (Client Error) responses indicates that a server is receiving a high volume of invalid or malformed HTTP requests that cannot be processed. A spike in errors might be caused by broken deployments, outdated API clients, or web scanning attempts.

Mitigation Options

Check for client misconfigurations, applications, scripts, or user agents that are sending malformed HTTP requests.

Check for identity provider issues or recent changes to Access Control Lists (ACLs) to avoid 401 (Unauthorized) or 403 (Forbidden) errors.

Validate load balancer and proxy rules to ensure requests are not being incorrectly dropped or rejected before reaching the web server.

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Detections

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Documentation

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