OS Exhaustion Flood
OS Exhaustion Flood [T1499.001]
Information
Introduction
OS Exhaustion Flood (T1499.001) is a sub-technique within the MITRE ATT&CK framework under the "Endpoint Denial of Service" (T1499) category. This method involves overwhelming the targeted operating system resources, such as open file descriptors, memory, CPU cycles, or network connections, to degrade or completely deny legitimate services. Attackers typically leverage this tactic to disrupt business continuity, distract defenders, or facilitate subsequent malicious activities.
Deep Dive Into Technique
Attackers employing OS Exhaustion Flood techniques aim to saturate critical operating system resources, causing denial of service conditions. Common execution methods and mechanisms include:
File Descriptor Exhaustion:
Attackers open numerous file descriptors by initiating multiple file handles or sockets without properly closing them.
Eventually, the operating system reaches its limit, preventing legitimate processes from opening new files or sockets.
Memory Exhaustion:
Attackers intentionally consume available memory resources by spawning multiple processes or threads, allocating large data structures, or using memory-intensive operations.
This forces the OS into a state of memory starvation, leading to instability or crashes.
CPU Resource Exhaustion:
Attackers run computationally intensive tasks or infinite loops, consuming available CPU cycles.
This causes legitimate processes to slow down significantly or become unresponsive.
Network Connection Exhaustion:
Attackers establish numerous simultaneous TCP connections, leaving them open or semi-open (e.g., SYN flood attacks).
This exhausts the OS connection table, preventing legitimate users from establishing new connections.
Real-world procedures often involve automated scripts, custom malware, or publicly available tools designed explicitly to exhaust OS resources. Attackers typically leverage botnets or compromised systems to amplify the volume and intensity of these attacks.
When this Technique is Usually Used
Attackers commonly utilize OS Exhaustion Flood techniques in various scenarios and stages:
Disruption of Services:
Directly targeting critical infrastructure, web servers, application servers, or database servers to cause downtime and business disruption.
Distraction and Diversion:
Creating noise or chaos to distract security personnel from detecting more subtle, sophisticated attacks occurring simultaneously or subsequently.
Extortion and Ransom:
Threat actors may threaten or execute denial of service attacks to coerce organizations into paying ransom demands.
Competitive Advantage:
Malicious actors targeting competitors to disrupt their online presence, operations, or customer trust.
Cyber Warfare and Hacktivism:
Nation-state actors or hacktivist groups employing OS Exhaustion Flood attacks to disrupt critical national infrastructure or to make political statements.
How this Technique is Usually Detected
Detection of OS Exhaustion Flood techniques typically involves proactive monitoring and anomaly detection using various tools and methodologies:
Resource Monitoring Tools:
System monitoring utilities (e.g., Nagios, Zabbix, Prometheus) to detect unusual spikes in CPU, memory, file descriptor usage, or network connections.
Network Traffic Analysis:
Intrusion Detection Systems (IDS) or Network Intrusion Prevention Systems (NIPS) such as Snort, Suricata, or Zeek to identify anomalous network traffic patterns indicative of flooding attacks.
Endpoint Detection and Response (EDR):
Tools like CrowdStrike Falcon, Carbon Black, or Microsoft Defender to detect unusual process behavior, abnormal resource consumption, or suspicious system calls.
Log Analysis and SIEM Solutions:
Security Information and Event Management (SIEM) platforms (e.g., Splunk, ELK Stack, IBM QRadar) aggregating logs from multiple sources to detect anomalies in system resource utilization and alert on suspicious activities.
Indicators of Compromise (IoCs) specific to OS Exhaustion Flood include:
Sudden and sustained spikes in CPU, memory, or file descriptor usage.
Excessive number of connections from single or multiple IP addresses.
Unusual increases in open files, sockets, or processes.
System logs indicating resource exhaustion errors (e.g., 'Too many open files', 'Out of memory', 'Connection refused').
Why it is Important to Detect This Technique
Early detection of OS Exhaustion Flood is critical due to the significant impacts it can have on an organization's systems and networks:
Service Downtime and Loss of Availability:
Prolonged denial of legitimate services, resulting in business disruption, customer dissatisfaction, and potential revenue loss.
Operational Disruption:
Reduced productivity and operational efficiency due to system instability, crashes, or degraded performance.
Financial and Reputational Damage:
Significant financial losses from downtime, recovery costs, potential regulatory fines, and long-term damage to brand reputation.
Security Posture Weakening:
Attackers may use OS Exhaustion Flood attacks as a distraction, facilitating more stealthy and damaging cyber-attacks, such as data breaches or lateral movement within the network.
Compliance and Regulatory Impact:
Organizations may face compliance violations or regulatory scrutiny if critical services are disrupted or data integrity is compromised due to resource exhaustion.
Examples
Real-world examples of OS Exhaustion Flood attacks include:
SYN Flood Attacks:
Attackers send numerous TCP SYN packets to initiate handshakes without completing them, exhausting the target's connection queue.
Tools commonly used: hping3, LOIC (Low Orbit Ion Cannon).
Impact: Legitimate users unable to establish new connections, causing service downtime.
Slowloris Attack:
Attackers open multiple HTTP connections, sending partial requests to keep connections alive indefinitely, exhausting available connections.
Tools commonly used: Slowloris script, OWASP HTTP DoS Tool.
Impact: Web servers become unresponsive, denying legitimate user access.
File Descriptor Exhaustion Attacks:
Malware or scripts intentionally open numerous files or network sockets without closing them, exhausting OS file descriptor limits.
Example: Custom malware observed in targeted attacks, leveraging scripts or botnets.
Impact: Application crashes, inability to open new files or sockets, denial of service conditions.
Memory Exhaustion Attacks (Memory Bombs):
Malicious processes rapidly allocate large amounts of memory.
Example: Fork bombs (e.g.,
:(){ :|:& };:in Unix-based systems).Impact: System instability, crashes, and inability to execute legitimate processes.
CPU Exhaustion Attacks:
Malicious actors execute infinite loops or computationally intensive tasks.
Example: Cryptocurrency mining malware, intentionally misconfigured scripts.
Impact: Severe degradation of performance, legitimate applications become unresponsive or unusable.
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