Denial of Service - DoS attack
A Denial of Service (DoS) attack on a mainframe system aims to make a z/OS system, its applications, or network resources unavailable to legitimate users by overwhelming it with excessive requests or data, consuming critical resources, or exploiting vulnerabilities. The primary goal is to disrupt the availability and performance of critical enterprise services hosted on the mainframe. A Denial of Service (DoS) attack in the mainframe context is a malicious attempt to make an IBM z/OS system, its applications (like CICS, IMS, DB2), or network services unavailable to legitimate users. Its primary goal is to disrupt the availability of critical business functions by overwhelming system resources or exploiting vulnerabilities, rather than stealing data.
Key Characteristics
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- Resource Exhaustion: DoS attacks often target finite mainframe resources such as CPU cycles, memory (storage), I/O channels, network buffers, or application-specific resources like CICS transaction slots or DB2 connections.
- Network Saturation: Flooding the z/OS TCP/IP stack with a high volume of traffic (e.g.,
SYNfloods,UDPfloods) can consume network bandwidth and processing power, preventing legitimate connections to mainframe services. - Application Overload: Attacks can specifically target mainframe applications (e.g., CICS regions, IMS message processing regions, DB2 stored procedures) by sending a large number of requests designed to consume their internal resources or exploit inefficient processing paths.
- Impact on Availability: The direct consequence is the degradation or complete cessation of critical business services hosted on the mainframe, leading to significant financial and reputational damage.
- Single Source (typically): While Distributed DoS (DDoS) involves multiple sources, a traditional DoS attack typically originates from a single attacker or a limited number of sources, making it potentially easier to identify and mitigate.
Use Cases
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- TCP/IP Stack Flooding: An attacker might send a massive number of
SYNpackets to the z/OS Communications Server, attempting to exhaust the connection table and prevent new, legitimate connections to CICS, DB2, or other network services. - CICS Transaction Flooding: Repeatedly invoking a resource-intensive CICS transaction (e.g., one that performs complex database queries or extensive file I/O) from a single source can consume CICS region CPU, storage, and transaction slots, impacting other users.
- DB2 Connection Exhaustion: An external attack that rapidly attempts to establish and hold a large number of concurrent DB2 connections can exhaust the maximum allowed connections for a DB2 subsystem, preventing legitimate applications from connecting.
- IMS Message Queue Overflow: Sending a high volume of messages to an IMS transaction queue can overwhelm the Message Processing Regions (MPRs), causing message backlogs, slow response times, or even system instability.
- TCP/IP Stack Flooding: An attacker might send a massive number of
Related Concepts
DoS attacks are fundamentally a security concern related to the availability aspect of the CIA triad (Confidentiality, Integrity, Availability). They are mitigated through robust network security configurations on the z/OS TCP/