Signs Your Site Is Under an HTTP Flood Attack
Website performance and availability are vital for businesses, especially in an increasingly digital world. One of the most deceptive and damaging threats you may encounter is the HTTP flood attack—a type of Layer 7 DDoS (Distributed Denial of Service) attack. These attacks don’t aim to clog your internet connection but rather to exhaust your application and server resources by mimicking real user behavior.
Recognizing the early signs of such an attack is essential. The sooner you detect it, the faster you can mitigate the damage and keep your services online.
What Is an HTTP Flood Attack
An HTTP flood attack targets the application layer of the OSI model. Rather than overwhelming the network with data, attackers send a large volume of legitimate-looking HTTP requests (often GET or POST) to overload the server. These requests can trigger resource-heavy actions like page rendering, database queries, or session initiation. When performed at scale, the server becomes slow, unresponsive, or completely unavailable—even if total traffic volume appears normal.
Because these attacks use standard web traffic patterns, they can bypass traditional DDoS defenses and appear harmless to the untrained eye.
Why HTTP Flood Attacks Are Hard to Detect
Unlike volumetric DDoS attacks, HTTP floods do not necessarily generate high bandwidth consumption. They often originate from legitimate IP addresses or compromised devices and simulate normal user behavior. This makes it difficult for automated systems to distinguish between real and malicious traffic. The goal is to exhaust server-side resources, not to flood the network itself.
This stealthy nature allows HTTP floods to continue longer without detection, silently degrading performance and causing frustration for users and administrators alike.
Unusual Website Slowness or Timeout Errors
A sudden decrease in website performance or an increase in page load times without a corresponding spike in user activity may indicate a flood attack. In severe cases, legitimate users may encounter 503 (Service Unavailable) or 504 (Gateway Timeout) errors. If these issues appear during low-traffic periods or outside of business hours, it’s a strong signal something is wrong behind the scenes.
Abnormal Server Resource Consumption
Another early sign of an HTTP flood attack is an unexpected increase in server resource usage. Watch for spikes in CPU, memory, or disk I/O without a matching increase in user sessions or application usage. These are indicators that backend resources are being taxed beyond normal limits, possibly due to excessive and malicious requests.
Repetitive and High-Frequency HTTP Requests
If you review your server logs and notice a pattern of repeated HTTP GET or POST requests to specific pages or actions—such as login pages, search functions, or dynamic content endpoints—it could be part of an HTTP flood. These endpoints often require heavier server processing, making them prime targets for exploitation.
High Number of Open Sessions or Connections
HTTP floods often involve bots or compromised devices initiating and holding multiple simultaneous sessions. This can lead to an unusually high number of active connections to your application. If your server struggles to manage sessions, or if session timeouts are unusually long, it could signal that the system is under attack.
Discrepancies in Traffic Behavior
Another clear warning sign is strange or inconsistent user behavior. This may include a surge in traffic from a single country, many users avoiding scripts and images, or visits where no meaningful interaction takes place. If your analytics show odd session durations, bounce rates, or navigational paths, investigate further—this behavior may not be human.
How to Respond to an HTTP Flood Attack
If you suspect an HTTP flood is occurring, quick response is crucial. Start by enabling rate limiting to throttle request volumes per IP or session. Implement a web application firewall (WAF) to detect and block suspicious traffic based on request patterns. You can also use CAPTCHAs or JavaScript challenges to distinguish real users from bots. Cloud-based DDoS mitigation tools can provide additional layers of protection.
Work with your hosting or CDN provider to identify and block malicious IP addresses and deploy automated protection rules. If your infrastructure supports real-time analytics, use them to identify behavioral anomalies as early as possible.
Conclusion
HTTP flood attacks represent a new wave of subtle, intelligent, and highly effective denial-of-service attacks. Unlike traditional DDoS methods that rely on brute force and high bandwidth, HTTP floods exploit the very way your applications are designed to serve content. They’re quiet, persistent, and can go unnoticed for hours or even days if you’re not looking at the right indicators.
Being aware of the signs—such as server slowdowns, resource spikes, repetitive requests, and odd traffic patterns—can help you take early action. As attacks become more sophisticated, businesses need to implement proactive, behavior-based defenses and continuously monitor traffic patterns to ensure resilience.