Endpoint Denial of Service: Service Exhaustion Flood

Adversaries may target the different network services provided by systems to conduct a DoS. Adversaries often target DNS and web services, however others have been targeted as well.[1] Web server software can be attacked through a variety of means, some of which apply generally while others are specific to the software being used to provide the service.

One example of this type of attack is known as a simple HTTP flood, where an adversary sends a large number of HTTP requests to a web server to overwhelm it and/or an application that runs on top of it. This flood relies on raw volume to accomplish the objective, exhausting any of the various resources required by the victim software to provide the service.[2]

Another variation, known as a SSL renegotiation attack, takes advantage of a protocol feature in SSL/TLS. The SSL/TLS protocol suite includes mechanisms for the client and server to agree on an encryption algorithm to use for subsequent secure connections. If SSL renegotiation is enabled, a request can be made for renegotiation of the crypto algorithm. In a renegotiation attack, the adversary establishes a SSL/TLS connection and then proceeds to make a series of renegotiation requests. Because the cryptographic renegotiation has a meaningful cost in computation cycles, this can cause an impact to the availability of the service when done in volume.[3]

ID: T1499.002
Sub-technique of:  T1499
Tactic: Impact
Platforms: AWS, Azure, Azure AD, GCP, Linux, Office 365, SaaS, Windows, macOS
Data Sources: Netflow/Enclave netflow, Network device logs, Network intrusion detection system, SSL/TLS inspection, Web application firewall logs, Web logs
Impact Type: Availability
Version: 1.0
Created: 20 February 2020
Last Modified: 29 March 2020

Mitigations

Mitigation Description
Filter Network Traffic

Leverage services provided by Content Delivery Networks (CDN) or providers specializing in DoS mitigations to filter traffic upstream from services.[4] Filter boundary traffic by blocking source addresses sourcing the attack, blocking ports that are being targeted, or blocking protocols being used for transport.

Detection

Detection of Endpoint DoS can sometimes be achieved before the effect is sufficient to cause significant impact to the availability of the service, but such response time typically requires very aggressive monitoring and responsiveness. Typical network throughput monitoring tools such as netflow, SNMP, and custom scripts can be used to detect sudden increases in circuit utilization.[5] Real-time, automated, and qualitative study of the network traffic can identify a sudden surge in one type of protocol can be used to detect an attack as it starts.

In addition to network level detections, endpoint logging and instrumentation can be useful for detection. Attacks targeting web applications may generate logs in the web server, application server, and/or database server that can be used to identify the type of attack, possibly before the impact is felt.

Externally monitor the availability of services that may be targeted by an Endpoint DoS.

References