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Stop Slowloris and Slow HTTP Attacks on Your Web Server

Slowloris doesn’t need massive bandwidth — it exhausts your server by holding connections open with trickle-rate data. PowerWAF detects and terminates slow connections at the edge before your server runs out of sockets.

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DDoS / Slow HTTP

Death by a Thousand Open Connections

Slow HTTP attacks are the assassin’s blade of DDoS — silent, efficient, and devastating. Instead of flooding your network with traffic, they open thousands of connections and keep each one alive by sending data at an impossibly slow rate. Your server patiently waits for each request to complete, tying up threads and sockets until no new connections can be accepted.

1 Mbps is all the bandwidth needed to take down an unprotected Apache server with Slowloris

The attack is invisible to network monitoring — bandwidth looks normal, packet rates are low, and each individual connection appears legitimate. Only application-layer analysis can detect the pattern of deliberate slowness that characterizes these attacks.

CWE-400 (Resource Exhaustion) OWASP Slow HTTP

How Slow HTTP Attacks Work

Five techniques that exhaust your server with almost zero bandwidth.

🐢

Slowloris (Partial Headers)

Sends HTTP headers one byte at a time, never completing the request. Each connection holds a server thread indefinitely.

GET / HTTP/1.1\r\nHost: target.com\r\nX-a: [1 byte/90s]...
📤

Slow POST (R-U-Dead-Yet)

Sends a legitimate Content-Length header but delivers the body at 1 byte per second, occupying the connection for hours.

POST /login Content-Length: 100000 [body: 1 B/s]
📥

Slow Read

Sends a legitimate request but reads the response at an extremely slow rate, forcing the server to keep the connection open.

TCP window size: 1 byte (reading response at 1 B/s)
📄

Apache Range Header

Sends requests with overlapping byte-range headers that force the server to generate massive multipart responses.

Range: bytes=0-1,1-2,2-3,...,9999-10000
🔄

Keep-Alive Abuse

Opens connections with Keep-Alive headers and sends requests at the slowest possible rate to keep them open indefinitely.

Connection: Keep-Alive [1 request per timeout window]

How PowerWAF Stops Slow Attacks

Five protection layers that terminate slow connections before they exhaust your server.

⏱️

Header Timeout Enforcement

Requires HTTP headers to complete within a strict time window (seconds, not minutes). Partial headers that trickle in are terminated immediately.

Stops Slowloris partial header attacks
📊

Minimum Data Rate

Enforces a minimum transfer rate for request bodies. Connections sending data below the threshold are identified as slow attacks and terminated.

Stops Slow POST / R-U-Dead-Yet attacks
⏰

Request Body Timeout

Sets a maximum time for complete request body delivery based on Content-Length. Oversized bodies with slow delivery are rejected.

Stops slow body delivery attacks
🔒

Connection Limits per IP

Caps the number of concurrent connections from a single IP address. Prevents a single attacker from monopolizing your connection pool.

Stops connection pool exhaustion
🧠

Behavioral Pattern Detection

Identifies the distinctive pattern of slow attacks: many connections from the same IP, all with identical slow data rates and incomplete requests.

Detects coordinated slow attack campaigns

Protected in Minutes, Not Months

No server reconfiguration. No module installation. No timeout tuning.

1

Point DNS

Route traffic through PowerWAF. All connection management happens at the edge.

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2

Instant Protection

PowerWAF immediately enforces timeouts and rate minimums on all incoming connections.

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3

Monitor Everything

Dashboard shows terminated slow connections, attacker IPs, and connection pool health.

Protects Apache, Nginx, IIS, Tomcat, Node.js, and any other web server — without touching server config.

See PowerWAF in Action

Real-time view of slow HTTP attacks being detected and terminated at the edge.

powerwaf-connection-log — live
07:18:01 TERMINATED 198.51.100.87 GET / (headers incomplete after 5s) → Slowloris: partial headers
07:18:02 TERMINATED 198.51.100.87 POST /login (body: 12 bytes in 30s, expected 50KB) → Slow POST attack
07:18:03 ALLOWED 203.0.113.50 GET /products (complete in 45ms) → Legitimate request
07:18:04 TERMINATED 198.51.100.23 Connection limit exceeded (847 concurrent from this IP) → Connection pool attack
07:18:05 TERMINATED 203.0.113.42 GET / (TCP window: 1 byte, slow read) → Slow Read attack
07:18:06 ALLOWED 198.51.100.12 POST /api/orders (body: 2KB in 120ms) → Legitimate API request
07:18:07 TERMINATED 198.51.100.87 GET / Range: bytes=0-1,1-2,2-3,...,999-1000 → Range header abuse

Simulated log showing PowerWAF terminating slow connections while legitimate traffic completes normally.

Proven Protection at Scale

< 5 minAverage setup time — DNS change only
0Server configuration changes required
24/7Continuous connection monitoring

Real-World Scenarios

Apache Server Under Slowloris Attack

An Apache server with default MaxClients of 256 is targeted by a Slowloris attack using 300 connections. Within minutes, all worker threads are occupied with half-open connections. PowerWAF terminates incomplete requests at the edge, keeping all 256 threads available for real users.

Node.js Event Loop Saturation

A Node.js application receives thousands of slow POST requests with large Content-Length headers. The event loop becomes saturated handling the trickle of incoming data. PowerWAF enforces minimum data rates and body timeouts, terminating slow requests before they reach Node.

Shared Hosting Under Attack

A shared hosting environment serves hundreds of websites on the same Apache instance. A Slowloris attack against one site takes down all sites on the server. PowerWAF protects the entire server by terminating slow connections at the proxy layer.

Protects any web server

Apache
Nginx
IIS
Tomcat
Node.js
LiteSpeed
Caddy
Gunicorn
uWSGI
Custom Servers

Frequently Asked Questions

What is a Slowloris attack?
Slowloris holds many HTTP connections open by sending partial headers, never completing the request. Each connection occupies a server thread, and with enough connections, the server’s pool is exhausted. The attack requires minimal bandwidth.
How is Slowloris different from a regular DDoS?
Regular DDoS overwhelms with volume. Slowloris uses very little bandwidth but holds connections open indefinitely. A single attacker can take down an Apache server by maintaining a few thousand half-open connections.
Which web servers are vulnerable?
Apache is most vulnerable due to its thread-per-connection model. Nginx and Node.js are more resilient but can be affected by slow POST attacks. IIS and Tomcat are vulnerable with default settings. PowerWAF protects all server types.
How does PowerWAF stop slow HTTP attacks?
PowerWAF enforces strict connection timeouts, minimum data rates for request bodies, concurrent connection limits per IP, and behavioral pattern detection — terminating slow connections at the edge before they reach your server.
Can Slowloris affect cloud-hosted apps?
Yes. Load balancers may forward half-open connections to backend instances. Auto-scaling may trigger, increasing costs. PowerWAF terminates slow connections at the edge before they reach your cloud infrastructure.
Do I need to reconfigure my web server?
No. PowerWAF operates as a reverse proxy, handling all connection management at the edge. Slow attacks are terminated before they reach your web server regardless of configuration.

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Keep Your Server Online — No Matter What

No credit card required. No server changes. Set up in under 5 minutes.

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