What is an application layer DDoS attack?
An application-layer DDoS attack is a malicious attempt to overwhelm web applications by exploiting Layer 7 of the OSI model. It targets specific application vulnerabilities to disrupt service availability.
Unlike network-layer attacks that flood infrastructure, application-layer incidents overwhelm specific application processes, consuming significant computing power. By mimicking legitimate user traffic and patterns, these attacks can maximize impact while requiring very little attacker bandwidth.
The most common vectors exploit inherent application vulnerabilities or weaknesses in application-level protocols like HTTP and HTTPS. Such attacks often abuse resource-intensive processes, such as database queries, authentication mechanisms, or search functionalities, creating unsustainable workloads that disrupt operations.
Application layer DDoS Attack vs. DNS amplification
While DDoS and DNS amplification attacks share the same objective of disrupting services, the exact methods can vary dramatically. Recognizing these differences is essential for devising the right defense strategy. Let’s compare these major DDoS types:
Attack mechanism: Application layer attacks directly target web application resources like search forms or authentication portals. By flooding these with fake requests, attackers consume excessive computing capacity, slowing or crashing apps. In contrast, DNS amplification abuses misconfigured DNS servers to achieve dramatic traffic multiplication.
Resource consumption: With application-layer attacks, consumption centers on application server resources, including memory, CPU, and disk I/O for logging and data access. DNS amplification overwhelms network infrastructure, such as firewalls and load balancers, by boosting traffic through misconfigured DNS servers. While traffic is amplified 50-100x, very little workload lands on application servers.
Traffic characteristics: DDoS application attacks mimic normal user patterns, comprising high volumes of HTTP/HTTPS requests to application entry points. DNS amplification uses continuous streams of unsolicited UDP traffic.
Protocol targeting: Application attacks operate at Layer 7, targeting web-facing resources. DNS amplification manipulates UDP-based DNS queries to achieve traffic magnification.
Complexity: Application layer attacks require more effort to put together. Attackers analyze applications to uncover vulnerabilities, focusing on aspects that can be exploited to disrupt operations. DNS assaults simply spoof addresses and rely on inherently vulnerable servers. A hacker can launch a high-volume attack with little setup or knowledge of your network or services.
How application layer DDoS attacks take place
Application layer DDoS attacks achieve disruption through precise, targeted exploits rather than brute force. Instead of flooding networks, these application-specific assaults create bottlenecks by overloading vulnerabilities at key weak points. Below is a detailed breakdown of how these attacks operate:
Floods connection endpoints: Attackers will bombard infrastructure connection points like proxies and load balancers. By flooding sockets and sessions with more requests than applications can handle, assaults consume all available connections, creating a denial-of-service effect for legitimate users.
Exploits authentication processes: Validation checks like CAPTCHAs, multi factor authentication, or account lockouts are prime targets. Aggressors continuously submit login requests to overwhelm these mechanisms by triggering account restrictions or consuming all authentication server resources.
Manipulates API request complexity: APIs have built-in limits on call complexity to manage server load. DDoS application layer attacks abuse these limits by maximizing expensive requests. For example, they might call product recommendation APIs with excessive unmatched parameters.
Mimics legitimate traffic patterns: To avoid defenses, hackers mimic customer or user behavior by spacing requests appropriately and using valid credentials when possible. The traffic resembles genuine interactions, such as browsing, searching, or submitting forms. This attack makes malicious traffic blend in better than traditional volume-based attacks.
Targets specific application vulnerabilities: Perpetrators research and probe apps to uncover application-specific weaknesses suited for exploitation. For example, they might find that search queries with wildcard parameters consume excessive resources.
Consumes database resources: Databases often have significant processing requirements. Attacks employ expensive queries, search filtering, and database joins to create an overwhelming workload, causing delays and potentially disrupting the connection between the application and its data.
Disrupts session management: Web apps track user sessions to maintain state. The process is resource-intensive, as it often involves allocating memory and handling cookies. Hackers initiate thousands of fake sessions and rapid timeouts to exhaust server resources for tracking user state.
9 ways to defend against application layer DDoS attacks
With application layer attacks becoming increasingly sophisticated, you need a multi-faceted defense strategy. This involves using proactive measures to harden infrastructure and reactive techniques to detect and mitigate ongoing attacks. Let's explore some key mechanisms for protecting against these assaults:
1. Implement JavaScript challenge mechanisms
Adding JavaScript challenges can effectively distinguish bots from legitimate users. These prompts analyze visitor behavior for automation indicators. If automation is detected, additional verification tests will be activated to confirm legitimacy before granting further access. Test these systems rigorously to avoid hindering legitimate customers.
2. Deploy advanced Next-Gen WAFs (Web Application Firewalls)
Next-Gen WAFs use application-specific rulesets to identify and block malicious traffic. Properly tuned WAFs can flag abnormalities in request complexity, geolocation, session management, input sizes, and more. Consider using cloud-based Next-Gen WAFs to leverage shared threat intelligence for faster attack detection.
3. Use IP reputation filtering
IP reputation databases maintain up-to-date botnet and malware IP lists. Web applications can automatically block traffic from known malicious sources by referencing these databases. Ensure the database remains updated frequently as botnet IP addresses change rapidly.
4. Implement rate limiting at the application level
Rate limiting enforces thresholds for traffic volumes and request complexity while blocking offenders. For example, you can set limits on API calls per IP, concurrent sessions per user, or database reads per minute. Granular limits help resist sudden spikes while preserving legitimate access.
5. Create intelligent CAPTCHA verification
Standard CAPTCHAs are limited in their bot detection capabilities. Intelligent CAPTCHAs powered by machine learning can more accurately identify automated tools by analyzing mouse movements, input patterns, and more. As attackers regularly shift tactics, you should continuously train your CAPTCHA system using the latest data on bot behaviors.
6. Configure browser integrity checks
Examine incoming traffic for consistent browser fingerprinting. Requests lacking legitimate browser characteristics can be selected for additional verification or blocked completely. Browser integrity checks help ensure traffic originates from authentic sources.
7. Use machine learning traffic analysis
Machine learning techniques create precise models of normal versus abnormal traffic patterns. Continuously training these systems on updated data improves detection accuracy. Frequent retraining ensures the models adapt to evolving traffic trends.
8. Implement token-based request verification
Tokenized keys with strict expiration timeframes validate that each API call originates from your legitimate frontend. Attacks attempting to bypass the front end are blocked as they lack valid tokens. Tokens should match session details to prevent replay attacks and unauthorized requests.
9. Use adaptive traffic segmentation
Segmenting traffic by risk profile lets you isolate suspicious flows for further analysis while preserving application resources for legitimate users. Update risk models frequently to ensure accuracy and reflect the latest threat intelligence.
Protect your business with Fastly DDoS protection
As attackers increasingly exploit vulnerabilities in Layer 7 business logic, you must employ an array of adaptive defense strategies. No single solution provides comprehensive protection, but combining proactive and reactive mitigation techniques at the edge can effectively counter application attacks before they overwhelm infrastructure. Intelligent capabilities like machine learning and behavior analysis are beneficial for keeping up with the growing sophistication of malicious botnets and stressor services.
Fastly's DDoS Protection services provide a powerful yet flexible approach for shielding your web properties and APIs. Backed by a global edge network, the solution offers deep visibility into traffic combined with rapid threat detection and mitigation capabilities. Here's how the platform helps your business stay ahead of these threats:
Automatic mitigation of attacks: Fastly uses proactive techniques to automatically identify and neutralize DDoS attacks without requiring manual intervention. Threats are addressed immediately, minimizing disruption.
Improved resilience: With Fastly’s solution, applications, and APIs maintain consistent performance and availability, even during high-volume attacks. This resilience ensures a swift customer experience for legitimate traffic.
Dynamic detection and adaptive identification: Fastly continuously monitors incoming traffic, using advanced analytics to detect anomalous attack patterns instantaneously. Adaptive identification ensures the solution stays effective against evolving threats.
Zero attack fees: Fastly doesn't charge for attack traffic, unlike many providers. You only pay for legitimate requests, keeping operational costs predictable and reducing financial strain during prolonged attacks.
Integrated next-gen WAF: Fastly's next-gen WAF complements DDoS protection by identifying and blocking malicious web requests.
Near instant mitigation: The platform reduces the impact of attacks on end users by mitigating threats in seconds.
Versatile deployment: Fastly protects applications of all sizes with fast, upgradable defenses.
Learn how Fastly can protect your applications, APIs, and microservices, ensuring your business stays secure and resilient to developing threats.
