API hooking lets software intercept or redirect selected function calls. An endpoint detection and response (EDR) product may use hooks in user space to inspect activity or influence execution, but hooking is only one possible monitoring technique—not a complete explanation of how every EDR works.
What API hooking means
An application programming interface (API) is a defined way for software components to request services or exchange information. A hook places an intermediary at a chosen function boundary. When a process makes a call, the intermediary can inspect the call and its parameters, then allow it to continue, change what happens, or redirect execution.
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In EDR, user-space API hooking can provide visibility into selected behavior as calls pass through monitored functions. A 2023 paper describes API hooking as a technique antivirus and EDR software use to monitor and control software execution on Windows. That describes a technique, not a universal implementation: it does not show that every EDR product uses hooks or monitors the same functions. The paper evaluated 16 commercial antivirus products and four EDR products; that is the study’s test scope, not a current market census.
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Inline hooking
An inline hook changes instructions in a function’s in-memory code so execution is redirected to a handler. The handler can inspect the call before execution continues or takes another path.
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IAT hooking
A process’s import address table (IAT) holds pointers to functions that the process uses from other modules. An IAT hook changes a relevant pointer so the call reaches a handler rather than the original function directly.
Both methods insert an intermediary into execution, but they do so at different places: inline hooks alter code at the function, while IAT hooks change a function pointer used by the process. MITRE ATT&CK’s Credential API Hooking reference describes these approaches in the context of credential capture. A technical thesis provides additional background on hooking mechanisms; its discussion should not be treated as current product guidance.
Why hooks are dual-use
The same interception concept can serve different purposes. Security software may use hooks to observe selected activity or control execution. Malicious software can use them to inspect function-call parameters or redirect execution. MITRE classifies credential API hooking as a credential-access technique because intercepted parameters may contain authentication data.
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How defenders can identify suspicious hooking
A hook is not inherently malicious, and a single signal does not establish that credential theft is taking place. MITRE’s detection strategy, DET0139, emphasizes correlating behaviors, including memory modifications, hook-installation functions, and suspicious module loads in credential-sensitive processes such as LSASS, Explorer, or Winlogon.
For Linux and macOS, the same strategy describes correlating environment-variable injection, unexpected library loads, and memory patching. The value is in the combination and context of these signals—not treating any one event as proof of malicious activity.
What API hooking does not tell you about an EDR
Knowing that hooking exists as a monitoring technique does not reveal which functions a particular product watches, which operating systems or processes it covers, or whether it records activity, blocks it, or changes execution. Those details depend on the product and its implementation. The sources here do not establish a current vendor-by-vendor comparison.
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When evaluating a specific EDR’s monitoring claims, look for documentation or controlled tests that identify the product version, operating system, monitored events, and response behavior. A finding from a study’s particular products and test environment should not be generalized to all current endpoint platforms. For example, the 2025 EvilEDR study should be interpreted in light of its stated experimental setup and results, rather than as a universal statement about EDR behavior.
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