This expanded network-connection popup shows information about the app and all the duration options for allowing or denying. The utility lets you drill down nearly everywhere. Click a button here and there—like a downward-pointing arrow to the left of the Deny button—and you can expand options and limit choices.
An IP address is a destination, like an apartment building; a port is like a specific apartment within the building. Little Snitch comes configured to allow common activities. For example, Safari requests data from port 80 non-secure Web connections and port https connections to pass through without notice. Many OS X system daemons, autonomous bits of low-level software, also get pre-approved.
But even these passes are explicitly allowed via rules that you can view, with descriptions, in the Little Snitch Configuration app. You can be concerned enough about Internet safety that you changed prefab rules, like requiring individual approval of domain access in Safari, instead of letting it use all those ports.
But it quickly settles down, even if you use a variety of software. We use cookies and other tracking technologies to improve your browsing experience on our site, show personalized content and targeted ads, analyze site traffic, and understand where our audiences come from. To learn more or opt-out, read our Cookie Policy. Last week I finally installed Little Snitch , a long-running Mac utility that lets you track every connection in and out of your computer. The latest version, released in July, comes with a map of where each connection is headed geographically, which is what convinced me to take the plunge.
Now, Little Snitch can give you a physical representation of every IP your computer connects with. It will even light up particular paths when a new connection is made, a visual guide to all the invisible handshakes taking place each second just to keep your programs running.
When you can see those connections, the internet starts to look different. The first thing I noticed was that there are a lot of them. Over the course of a few days, my computer made thousands of connections spanning 21 different countries.
Running Spotify in the background meant a steady stream of pings to Sweden, while MacOS meant even the tiniest tasks would phone home to San Francisco. The strangest connections came from my Chrome browser, as Little Snitch ran into the lattice of third-party tracking systems that undergird the modern web. Another, even more specific rule will deny this connection.
Sounds complicated? Just give it a try and then open the Rules Window. You will find that all the rules are already sorted according to their priority. Little Snitch enables you to create rules in many different ways and on many different hierarchical levels. This may lead to redundant rules or invalid rules. Suggestions help you with cleaning up your existing rule set, as well as with creating new rules. You will find the search box right above the rules in the Little Snitch Rules Window.
Type in some search term to filter all your rules. Sometimes the server is down or busy, sometimes you are not connected to the Internet at all. When you have ruled out those reasons, you should look into you Little Snitch Network Monitor. You will find a couple of very helpful search features to support your inquiry. In most cases, apps contact online services directly.
But sometimes they use an extra helper process which is created by the app. But if an app uses a helper process, you might not be able to link the name or icon of the process to the app which is affected by the problems. You will have to use the search features of Network Monitor to find out, which process causes the problems.
First you check if you can visit other websites or if you can reach twitter. If this works you should open Network Monitor in Little Snitch. Just change the responsible rule by clicking the allow icon.
Your browser should now be able to access twitter. Just give it a try! Assume that you are trying to manually update your browser.
A quick check reveals that no connections requested by Google Chrome are denied. It is possible that Google Chrome uses a helper process to look for updates on behalf of Google Chrome. At first, it might be impossible for you to identify the right process. The practical meaning of this is that an installed listener will be able to control whether a process typically a debugger can debug another process or not.
Little Snitch uses this feature to protect its processes from debuggers, code injectors, or anything else that needs to attach to a process including DTrace. First it allocates some memory for a structure described in the code comments that contains four function pointers the last four structure fields and some other unknown data. The first field contains the total number of running processes. The interesting thing is that this is a fake or non-functional callback! If we insert a breakpoint on this address it will never be hit when we try to attach a debugger to one of the protected Little Snitch processes.
What is happening? If we look at the second function it contains exactly the same code as the fake callback. The replacement function is shown below. One key question about this pointer switch is: when does it happen?
If the listener was already installed, this could be a dangerous operation since the above code has no locks and interrupts are enabled, so crashes could happen. The answer lies in code references. The pointer exchange function is called in the init method as we can see on previous picture code xref, while the listener is installed in a function call from start method address 0x The trick is that the init method is guaranteed to be called before any other method in the class, meaning that the pointer switch always occurs first.
This only fools the static analysis if we carelessly neglect to look at the disassembler code references. Just a cute trick that could be improved by obfuscating the listener install functions via function pointers All other arguments are ignored. If the process is currently being traced, it will exit with the exit status of ENOTSUP; other- wise, it sets a flag that denies future traces.
An attempt by the parent to trace a process which has set this flag will result in a segmentation violation in the parent. The following disassembly output comes from the Little Snitch Daemon binary and shows how a call to the sysctl anti-debug facility is implemented.
At the beginning of this code snippet we can see the pointer tested against a NULL value. To resolve the symbol, the first step is to deobfuscate a string since dlsym needs the symbol string as the second parameter. The following screenshot shows some of the obfuscated strings and their deobfuscated version found in the various Little Snitch binaries.
After the string is deobfuscated the symbol is resolved via dlsym , the function pointer is stored in the global variable, and finally the code executes the sysctl function pointer. Compare the disassembly with the QA note sample code and you can conclude that this code is implementing the described anti-debugging trick. Both the sysctl and ptrace anti-debugging tricks can be bypassed with a kernel extension such as Onyx The Black Cat , or by breakpointing the ptrace and sysctl functions and fixing the return values; this is only valid if you are starting the application under the debugger and not if attaching to already-running processes.
Another alternative is to patch or remove the kauth listener with a kernel debugger or with another kernel extension. The cookie size in version 3. I came up with the following crude structure description:. The function that allocates a new cookie is at address 0x10FF0 and is used only from the attach callback. The cookie in the first argument should be the same and we can verify it is the same telnet process PID.
For example, we can display the IP address the process is trying to connect to from the third argument using a small gdb scripted command. Previously there was a bypass using com. Socket filters are implemented at the kernel level, but Little Snitch users have to make a decision about each connection in a dialog running at user level. More about this to come.
This is the main class of the driver as we can also observe in the driver Info. This will be extremely useful when understanding its design. This matches what we saw previously in the anti-debugging pointer switching trick — the init and start methods are overridden; init has a call to the function that exchanges the pointers, and when the driver starts, the real kauth listener is installed in the start method.
What is the trick to rebuild the class from the disassembly output? IDA identifies the overridden methods with yellow color which have references to code implemented in the driver itself, while pink color identifies the class methods not overridden. From this information we can easily reconstruct the class structure. We can use the same technique to identify all the other classes created by Little Snitch.
The following picture describes the IORegistryDescriptorC1 class, with a few methods overridden and others added by Little Snitch developers.
Its subclasses C2, C3, C4 themselves override some methods, and also add new ones maybe a few also overridden from parent class? The reason for the different classes is that they are used by different userland clients — Little Snitch Daemon, Little Snitch Agent, Little Snitch Configuration, Little Snitch Network Monitor, and implement different features specific to each userland client. The IORegistryDescriptorC5 class serves a very specific purpose and thus is slightly different and interesting in its own way.
We will explain why later. When an application wants to establish a network connection, the socket filter will intercept it, then send some data about the connection to the user daemon which generates a user alert it is probably relayed internally to the Agent since the daemon runs as root , the user will click a button to make a decision about the connection, and then the decision will have to be relayed back to the kernel.
Little Snitch implements bidirectional communication channels — one from user applications to kernel, and another from kernel to user. In the first, the request is always user application initiated and can be used to transmit data to the kernel or receive data from the kernel possible for the same request to send data and receive data.
In the second channel, it is the kernel that initiates the data transmission technically it notifies user application that some data is ready to be read. In some scenarios there is no need for the second channel, since polling can be used to ask the kernel if new data is available. This might not be very efficient in some scenarios. This is the class that SimpleUserClient code uses to communicate between a driver and a user client application. The connection from user application is established using IOServiceOpen function.
The following code snippet shows how to open a connection to Little Snitch driver. The third parameter to IOServiceOpen is an integer defining the type of connection to be created. Little Snitch implements five different types, used to distinguish between the different clients.
To find the client types we need to disassemble each binary and trace the calls to IOServiceOpen. Establishing a connection from the user application is pretty simple and elegant. The following picture shows the logs from SimpleUserClient driver when it is loaded and a user client connects.
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