# HookCase: macOS function hooking beyond the DYLD_INSERT_LIBRARIES limits > HookCase is a C++ and Objective-C++ tool for debugging and reverse engineering macOS applications and the operating system itself, re-implementing and extending Apple's DYLD_INSERT_LIBRARIES so that any method in any module can be hooked, child processes follow automatically, and watchpoints are supported. It suits a reverse engineer who has hit the limits of the stock mechanism, and it is a poor fit if you need a drop-in library for a shipped application. **steven-michaud/HookCase** — Tool for reverse engineering macOS/OS X - Repository: https://github.com/steven-michaud/HookCase - Stars: 842 · Forks: 116 - Language: C++ - License: not declared - Published: 2026-10-20 · Updated: 2026-10-20 · Language: en - Canonical page: https://hysenlabs.com/projects/steven-michaud-hookcase ## The tool exists because the stock mechanism has edges HookCase is described as a tool for debugging and reverse engineering applications on macOS, and the operating system itself. The mechanism it replaces is the key to understanding it. The README says HookCase re-implements and extends Apple's DYLD_INSERT_LIBRARIES functionality, and then makes the comparison explicit: it can be used to hook any method in any module, even non exported ones, and even those that do not have an entry in their own module's symbol table. In a single operation it can be applied to a parent process and all its child processes, whether or not the child processes inherit their parent's environment. It supports watchpoints. So HookCase is considerably more powerful than DYLD_INSERT_LIBRARIES, and it also does not have the restrictions Apple has placed on DYLD_INSERT_LIBRARIES. That framing matters for how you should read the project. It is not a general purpose hooking library, and the README does not present it as one. It is a tool built by a reverse engineer, for reverse engineers, aimed squarely at the situations where the standard mechanism refuses to work. The person behind it is named in the README. Steven Michaud, 9/2025, and the project is MIT licensed according to the repository description, though the licence field is recorded as unknown, so the LICENSE file in the repository is the thing to read. The language is C++ with Objective-C++ in the topic list, which is what you would expect for a tool that has to work at the level of the dynamic loader and the Mach-O runtime. The last push to the repository was on 2026-05-14, and the repository has no GitHub releases, so the source tree is the distribution channel. ## Hooking a method with no symbol table entry is the hard case It is worth spending a paragraph on the specific capability the README leads with, because it is the one that separates this from a wrapper around the stock mechanism. A method in a Mach-O binary can be non exported, which means the symbol is not in the dynamic symbol table, and it can lack an entry in its own module's symbol table entirely, which means there is no name to look it up by. The ordinary route to interposing on a function, resolving a symbol by name at load time and replacing the implementation, has nothing to hook onto in those cases. Address based interception at a known call site, or a full blown instrumentation of the module, is what remains. The README also notes that HookCase works with applications that have entitlements, and links to Apple's entitlement documentation in making that point. That is the second edge of the stock mechanism, and it is the one most likely to matter for a modern macOS application. Apple hardened DYLD_INSERT_LIBRARIES over successive releases, and the hardening has a specific effect: processes that carry entitlements, which in practice means properly signed applications that use protected resources, will not honour an injected library. For a reverse engineer, that closes off the easiest path into a large class of targets. The README's claim is that HookCase does not carry these restrictions, which is a strong claim, and it is the one you would want to verify against your own target application before relying on it. That last point is also why the project is framed as a debugging and reverse engineering tool rather than a testing library. The audience is someone who already knows what they are looking at inside the binary. ## Child processes are followed even without inherited environment The second capability on the list is the one that will decide whether the tool is useful for a given investigation. The README says that in a single operation, HookCase can be applied to a parent process and all its child processes, whether or not the child processes inherit their parent's environment. The qualifier matters, because that is exactly where the ordinary mechanism fails. The environment variable that DYLD_INSERT_LIBRARIES relies on is passed down through the environment, which means a child that is launched with a sanitised environment, or by a launch mechanism that does not propagate it, will not be instrumented. In a debugging session where a parent process spawns helpers, daemons, or a child that re-executes itself, the parts you most wanted to see are the parts that do not inherit. HookCase's approach, as described, is to attach to the parent and follow the process tree, so the coverage does not depend on how the child was started. One operation, whole tree. This is the kind of feature that cannot be added to an existing mechanism from the outside, and it explains why this is a tool rather than a library. The repository layout backs up the same picture. Alongside the HookCase directory there is a call_orig directory, which is the convention for saving a pointer to the original implementation of a function you have replaced so you can call through to it, and a HookLibraryTemplate directory, which is a starting point for writing your own hook library. That call through capability is the practical counterpart of the hooking itself. Without it you can replace a function but not call the original, which is rarely enough for real analysis, and having a template in the repository means you do not have to work out the calling conventions from scratch. ## Watchpoints sit alongside the hooking The feature list is short, and watchpoints are on it. A watchpoint is a hardware assisted breakpoint that pauses execution when a specific memory location is read or written, rather than when a specific instruction address is reached. For a reverse engineer working on a data structure rather than a code path, that is the tool you want, because it answers the question of who modified this field rather than what called this function. The README's framing is that HookCase is considerably more powerful than DYLD_INSERT_LIBRARIES, and the watchpoint support is a big part of why that comparison is fair. DYLD_INSERT_LIBRARIES gives you interposition on symbols, which is a code level mechanism. Watchpoints are a data level mechanism, and the two answer different questions. The examples directory shows how broad the surface is. There are folders for dynamic-hooking, for events, for kernel-logging, for secinit, for watchpoints and for xpcproxy, and a top level example file exists for each of those areas, named examples-dynamic-hooking.md, examples-events.md, examples-kernel-logging.md, examples-secinit.md, examples-watchpoints.md and examples-xpcproxy.md. There is also an Examples/bugzilla1201401 directory, which by its name points at a specific reported bug. Reading the names tells you the scope of the tool: it goes past function hooking into the system services and the security machinery, including SecInit, which is the point at which a process initialises its security context, and XPC proxying, which is the interprocess communication mechanism on modern macOS. That is a much larger surface than a simple interposition library, and it is a much larger surface to audit before running it. ## The documentation is a set of numbered markdown files The README is essentially a table of contents, and the documentation lives in the repository as numbered markdown files. The list is 0-whats-new.md, 1-more-about.md, 2-building.md, 3-installing.md, 4-using.md, 5-resources.md and 6-examples.md, which is a sensible structure for a tool that has both a build story and a usage story. The structure tells you the shape of the project. There is a changelog section, a longer background section, a build document and an install document, a usage document, a resources document, and a document of worked examples that correspond to the example directories in the tree. Two consequences follow for anyone picking this up. First, there is no hosted documentation site and no wiki, so the docs move with the code and you have to read the version in the repository rather than a page that can be out of date. Second, since the build is a C++ and Objective-C++ project that works at the loader level, the build document is not skippable: expect to deal with a toolchain, and expect the install document to matter as much as the usage document. The genassym directory in the repository root is worth noting too. The name suggests assembly symbol generation, which is consistent with a project that has to operate at the level of Mach-O symbols and the dynamic linker. The README does not describe it, so what exactly it generates and when you need it is a question for the source. ## Version range, missing releases and an unclassified licence Three facts to check before you commit to this tool. The first is the version range. The README states that HookCase runs on OS X 10.9 Mavericks through macOS 26 Tahoe. That is a wide span, spanning the whole life of the platform, and the fact that it is stated in the README rather than in a support matrix is a sign of a project maintained by one person who knows which versions matter. The second is the release situation. There are no GitHub releases, and the last push to the repository was on 2026-05-14, roughly five months before this writing. The documentation set starts with a file called 0-whats-new.md, which is where the changelog lives, and that is the file to read to find out what state the tree is in. The third is the licence. The repository description records the licence as unknown, a custom one that GitHub cannot classify, with a pointer to the LICENSE file. For a tool of this kind, where you are going to build a dynamic library that gets injected into other processes, the licence terms and any warranty disclaimers are worth reading before you use it in an engagement. This is not a legal opinion, but it is a case where you want the text rather than a badge. The project also has a clearly stated purpose beyond the tool itself. The description calls it a tool for reverse engineering macOS and OS X, and the topics list assembly-language, c-plus-plus, dyld, kernel-modules, mach-o, macos, macosx, objective-c-plus-plus and reverse-engineering. The presence of kernel-modules in that list is a signal about how far the intended scope reaches, and about how much care the setup deserves. ## Conclusion HookCase suits a macOS reverse engineer who needs to intercept code that the standard dynamic loader mechanism cannot reach, including non exported methods, methods with no symbol table entry, and processes that do not inherit the environment they were launched from, since those are exactly the cases the README says it handles and where the stock mechanism is restricted. It does not suit an application developer looking for a stable instrumentation library, because there are no GitHub releases, the licence is not declared in a way GitHub can classify, and the documentation lives in numbered markdown files rather than a maintained reference site. Before you build against it, read the building and installing documents, 2-building.md and 3-installing.md, and check the version range against your machine, since the README states support from OS X 10.9 Mavericks through macOS 26 Tahoe, with the last push to the repository on 2026-05-14. ## FAQ ### What is HookCase used for? HookCase is a tool for debugging and reverse engineering applications on macOS and the operating system itself. It re-implements and extends Apple's DYLD_INSERT_LIBRARIES functionality so that any method in any module can be hooked, including non exported ones and those with no symbol table entry. ### How is HookCase different from DYLD_INSERT_LIBRARIES? The README states that HookCase is considerably more powerful: it can hook non exported methods and methods without a symbol table entry, applies to a parent process and all its child processes in a single operation whether or not the children inherit the parent environment, supports watchpoints, and does not carry the restrictions Apple has placed on DYLD_INSERT_LIBRARIES. ### Which macOS versions does HookCase support? The README states that HookCase runs on OS X 10.9 Mavericks through macOS 26 Tahoe. The last push to the repository was on 2026-05-14 and there are no GitHub releases. ### Where is the HookCase documentation? It is in the repository itself as numbered markdown files: 0-whats-new.md, 1-more-about.md, 2-building.md, 3-installing.md, 4-using.md, 5-resources.md and 6-examples.md, with worked examples for dynamic hooking, events, kernel logging, secinit, watchpoints and xpcproxy. ### Can HookCase hook applications that have entitlements? Yes. The README says HookCase does not have the restrictions Apple has placed on DYLD_INSERT_LIBRARIES, and gives applications with entitlements as the example of what the stock mechanism prevents. ## Sources - [Issues](https://github.com/steven-michaud/HookCase/issues) - [README](https://github.com/steven-michaud/HookCase/blob/master/README.md) - [steven-michaud/HookCase on GitHub](https://github.com/steven-michaud/HookCase) --- Hysen Labs editorial analysis, written from the project's own repository and release notes. Cite the canonical page: https://hysenlabs.com/projects/steven-michaud-hookcase