POST Flood Attack

A POST Flood Attack is a type of Distributed Denial of Service (DDoS) attack that targets the application layer (Layer 7 of the OSI model) by sending an overwhelming number of HTTP POST requests to a web server. Unlike traditional volumetric attacks that consume bandwidth, this method is designed to exhaust server resources such as CPU, memory, or application-specific processes.


This form of attack is particularly insidious because it mimics legitimate traffic, making it difficult to detect using conventional anomaly detection systems or rate-limiting protections.

Attack Methodology

  1. Connection Initiation: The attacker initiates multiple HTTP sessions, often via botnets or tools like LOIC, HOIC, or custom scripts.

  2. POST Request Flooding: Each session sends numerous HTTP POST requests with large payloads or incomplete data, often designed to keep the connection open for as long as possible.

  3. Server Exhaustion: Because POST requests typically require more server processing than GET requests—such as input validation, authentication checks, and writing to a database—this leads to rapid depletion of server-side resources.

  4. Persistence and Evasion: Attackers may randomize headers, use dynamic payloads, or employ rotating IPs to evade signature-based detection.

Common Targets

  • Login endpoints

  • Contact or registration forms

  • Search or comment submission pages

  • APIs requiring backend data processing

Indicators of Attack

  • Spike in POST requests without a corresponding increase in GET requests

  • Unusual patterns in request body sizes or content types

  • High CPU or memory usage on application servers

  • Sluggish performance or complete unavailability of dynamic pages

Mitigation Strategies

  1. Rate Limiting & Throttling

    Limit the number of POST requests per IP or session using Web Application Firewalls (WAFs) or API Gateways.

  2. Input Validation and Payload Inspection

    Use deep packet inspection (DPI) to analyze and filter suspicious request bodies.

  3. Behavioral Analysis

    Implement heuristics to flag sessions exhibiting automated behavior or prolonged connection durations.

  4. CAPTCHAs & JavaScript Challenges

    Deploy these mechanisms especially on public-facing forms to deter bots.

  5. Connection Timeouts

    Reduce the allowable time for a client to complete a POST body transmission.

  6. Anomaly Detection Systems

    Integrate machine learning-based systems that baseline normal POST traffic and trigger alerts when deviations occur.

by Sergei Penchuk, CISSP

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