winafl network fuzzingwinafl network fuzzing

When WinAFL finds a crash, the only thing it pretty much does is save the mutation in the crashes/ folder, under a name such as id_000000_00_EXCEPTION_ACCESS_VIOLATION. When I tried to start fuzzing RDPDR, there was a little hardship. If you are interested in that, there are other resources out there that will explain it well, such as articles, or even the official Microsoft specification itself. This article begins my three-part series on fuzzing Microsofts RDP client. III. Cyber attack scenario, Network Security. Finally, there are two kinds of Virtual Channels : static ones and dynamic ones. Where did I get it from? This talk describes our journey to make a traditional coverage-guided fuzzer (WinAFL) fuzz a complex network protocol - RDP. Argument register index may vary by target function, so it is given as executing option. 2 = Quite satisfied with my fuzzing campaigns (but there might be more to fuzz). Finally, before we start fuzzing, we should enable a little something that will be useful: PageHeap (GFlags). It is too easy for the fuzzer to mutate the BodySize field and break it, in which case most of the mutations go to waste. Use Winafl to fuzz jpeg2000 with the harness I built above: Looking at the interface Winafl we should be interested in some of the following parameters: - exec speed: the number of test cases that can be executed on 1s - stability: this indicator shows stability during fuzzing. Sometimes strange stuff just happens, like WinAFL itself randomly crashing and stopping the fuzzing in the middle of a week-end or something. Copy them andthe folder with DynamoRIO tothe virtual machine you are going touse for fuzzing. To better reproduce the crash, we implemented machine context and call stack dump when crush occurs. For RDP Fuzzing, we need server agent to receive fuzzer input, and send it back to client using WTS API. Finally, it is probably the most complex and interesting channel Ive had to fuzz among the few ones Ive studied! I still think it could have deserved a little fix. Here are the results after just three days of fuzzing: Here are the results after just three days of fuzzing: Even though you may have reached a plateau and WinAFL hasnt discovered a new path in days, you could wait a few additional hours and have a lucky strike in which WinAFL finds a new mutation. Your goal isto increase thenumber ofpaths found per second. to use Codespaces. vulnerabilities in real products. Using theVisual Studio command line, go tothe folder with WinAFL source code. The CClipRdrPduDispatcher::DispatchPdu function is where PDUs arrive and are dispatched based on msgType. If, like me, you opt for extra challenge, you can try fuzzing network programs. RDPSND PDU handler and dispatch logic in mstscax.dll. source directory). This state machine may be subdivided in several smaller state machines for each channel, but which would remain quite complicated to characterize. But what do we fuzz, and how do we get started? One ofthe approaches used toselect afunction for fuzzing isto find afunction that isone ofthe first tointeract with theinput file. Parse it (so that you can measure coverage of file parsing). Examples of mutations include bit flipping, performing arithmetic operations and inserting known interesting integers. We needed to choose a persistence mode: something that dictates how the fuzzer should exactly loop on our target function. To bypass this constraint, there exists a wonderful tool called RDPWrap. This is important because if the input file is sign in This option allows to collect coverage only from the thread of interest, which is the one that executed the target function. Heres what the architecture of the channels client implementation resembles: RDPDR channel architecture in mstscax.dll. This is easily done with the WTS API I mentioned earlier, which allows to open, read from and write to a channel. This PDU is used by the server to send a list of supported audio formats to the client. This time, we want to let WinAFL fuzz only the body part of the message. When theprogram execution reaches theend ofthe function, edit thearguments, align thestack, change theRIP/EIP tothe beginning ofthe function, etc. Virtual Channels (or just channels) are an abstraction layer in the Remote Desktop Protocol used to generically transport data. If you arent familiar with this software testing technique, check our previous articles: Similar toAFL, WinAFL collects code coverage information. This helps insituations when you make amistake, andthese functions are called not by themain executable module (.exe), but, for instance, by some ofyour target libraries. RDPWrap tampers with the server in order to allow local connections, and even concurrent sessions. It looks more like legacy. Then, if the iteration produced a new path, afl-fuzz will save the log into a file. Inthe above example, stability was 9.5%. the specific instrumentation mode you are interested in. This allows to know precisely in which function and which instruction a crash happened.

. In particular, were doing stateful fuzzing: the RDP client could be modelled by a complex state machine. The target takes files as input; so, thefirst thing I do after loading thebinary into IDA Pro isfinding theCreateFileA function inthe imports andexamining cross-references toit. As I was fuzzing CLIPRDR, I often had a problem in which my virtual machine would eventually freeze, and I couldnt do anything but hard reboot it. After installing Visual Studio, youll see inthe Start menu shortcuts opening theVisual Studio command prompt: (1) x86 Native Tools Command Prompt for VS 2019; and(2) x64 Native Tools Command Prompt for VS 2019. Also, it only works once (the payload wont work twice in the same RDP session), so the value of OutputBufferField should be premedidated we cant do small increments. It uses Frida to collect coverage against a running process between two points in time, and logs the output in a format readable by Lighthouse. Inaddition, there must bethe phrase: Everything appears to be running normally. The harness can assume this role by calculating and overwriting this BodySize field. This is easily done with a little trick: use cmdkey to store credentials (cmdkey -generic -user User -pass 123) and then start the RDP client with mstsc.exe /v . A corpus is a set of input files, or seeds, that we need to construct and feed to WinAFL to start. Were gonna have to manually reconstruct the puzzle pieces! The Remote Desktop Protocol is relevant now more than ever, having almost everyone started working remotely in 2020, and having Microsoft's Azure and Hyper-V platforms using it as the default remote connection protocol. Moving up thecall stack, I locate thevery first function that takes thepath tothe test file as input. A blind fuzzer, or blackbox fuzzer, is a fuzzer with no knowledge of a program's inner workings. Introduction In this blog post, I'll write about how I tried to fuzz the MSXML library using the WinAFL fuzzer. The greater isthe code coverage, thehigher isthe chance tofind abug. Crashes from RDP fuzzer is often not reproducible. This is a case of stateful bug in which a sequence of PDUs crashed the client, and we only know the last PDU. While I was working on this subject, other security researchers have also been looking for vulnerabilities in the RDP client. Lets examine themost important ofthem inorder. Modify the -DDynamoRIO_DIR flag to point to the Fuzzing feeds nonstandard data (either executable code, a dynamic library, or a driver) to a computer program in an attempt to cause a failure. Todo so, you can parallelize thefuzzer, play with thenumber offuzz_iterations, ortry tofuzz ina smarter way. It allows to copy several types of data (text, image, files) from server to client and from client to server. Aside from this engaging motive, most of vulnerability research seems to be focused on Microsofts RDP server implementation. But for abnormal targets, like system service or kernel module, SpotFuzzer can switch to agent mode, and inject an agent to the target for fuzzing. Therefore, we will use DynamoRIO, a well-known dynamic binary instrumentation framework. WinAFL has been successfully used to identify bugs in Windows software, such as the following: If you are building with DynamoRIO support, download and build user wants to fuzz) and instrumenting it so that it runs in a loop. The Remote Desktop Protocol provides multiplexed management of multiple virtual channels. not closed WinAFL won't be able to rewrite it. it takes thefile path as acommand line argument; and. Usually its in mstscax.dll, but it could also happen in another module. So lets dive into how RDP works and see for ourselves! In this case, we are only fuzzing whats below Header in the following diagram. At initialization and by default, the RDP client asks to open the four following SVCs: Dynamic Virtual Channels (or DVC) are built on top of the DRDYNVC Static Virtual Channel, which manages them. RDPDR is a Static Virtual Channel dedicated to redirecting access from the server to the client file system. 47 0. This is an interesting approach because sending a sequence of PDUs of different types in a certain order can help the client enter a state in which a bug will be triggered. but office don't have symbols (public symbols) which gives too much pain and too hard for tracing or investigating . fast target execution with clever heuristics to find new execution paths in So it seems that it is indeed used, rightfully, for security purposes. Everything works, everything is sunshine and rainbows, maybe weve even been lucky enough to find bugs. Thus, the two next steps are: With this in mind, I developed what I will call during the rest of this article the VC Server (for Virtual Channel Server). However, understanding which sequence of PDUs made the client crash is hard, not to say often a lost cause. In case of server fuzzing, if the server socket has the SO_REUSEADDR option set like the following code, then this may case 10055 error after some time fuzzing due to the accumulation of TIME_WAIT sockets when WinAFL restart the fuzzing process. Microsoft acknowledged the bug, but unsurprisingly closed the case as a low severity DOS vulnerability. For instance, sometimes small out-of-bounds reads will not trigger a crash depending on whats done with the read value, but can still hide a bigger looming threat. This video contain:1. Blind fuzzing vs Guided fuzzing. Therefore, the RDP client will receive a lot of different message types, in a rather random order. Static Virtual Channels (or SVC) are negotiated during the connection phase of RDP. You can easily bypass this protection by connecting to 127.0.0.2, which is equivalent. You can use these tags: 05:31. All aspects of WinAFL operation are described in the official documentation, but its practical use - from downloading to successful fuzzing and first crashes - is not that simple. 2021-08-26 Microsoft assessed the RDPDR malloc DoS bug as low-severity and closed the case. [], Multiple threads executing at once in semi-random order: this is harmless when the stability metric stays over 90% or so, but can become an issue if not. Second, kernel-level code has sig-nicantly more non-determinism than the average ring 3 Usual appearance of total paths found over time while fuzzing. execution. As weve seen in the fixed message type fuzzing strategy, the harness can be adapted to calculate the header for a given message type and wrap the headless mutation with this header. No luck. AFL is a popular fuzzing tool for coverage-guided fuzzing. We added some modification to fuzz Microsoft RDP client. Hence why all the functions are colored in red, but it is not very important. Dumped example is as follows. Shared memory is faster and can avoid some problems with files (e.g. Maybe this will lead me to new findings, and even a reproducible bug.. A drawback of this strategy is that crash analysis becomes more difficult. It turns out the client was actually causing memory overcommitment leading to RAM explosion. CVE-2018-20250, CVE-2018-20251, CVE-2018-20252, CVE-2018-20253, https://github.com/DynamoRIO/dynamorio/releases, https://github.com/googleprojectzero/winafl/blob/master/readme_pt.md, https://github.com/googleprojectzero/Jackalope/blob/6d92931b2cf614699e2a023254d5ee7e20f6e34b/test.cpp#L41, https://github.com/googleprojectzero/Jackalope/blob/6d92931b2cf614699e2a023254d5ee7e20f6e34b/test.cpp#L111, CVE-2018-12853, CVE-2018-16024, CVE-2018-16023, CVE-2018-15995, CVE-2018-16004, CVE-2018-16005, CVE-2018-16007, CVE-2018-16009, CVE-2018-16010, CVE-2018-16043, CVE-2018-16045, CVE-2018-16046, CVE-2018-19719, CVE-2018-19720, CVE-2019-7045, [CVE-2021-33599, CVE-2021-33602, CVE-2021-40836, CVE-2021-40837, CVE-2022-28875, CVE-2022-28876, CVE-2022-28879, CVE-2022-28881, CVE-2022-28882, CVE-2022-28883, CVE-2022-28884, CVE-2022-28886, CVE-2022-28887 ], (Let me know if you know of any others, and I'll include them in the list), Dynamic instrumentation using DynamoRIO (. Enabling this has been known to cause WinAFL is a fuzzer for Windows which can take a corpus of input files, track which code is executed, and generate new inputs to execute new execution paths. The tool combines However, it requires some more preparation: In conclusion, its nice to try both fuzzing approaches for a channel. As mentioned, analyzing a crash can range from easy to nearly impossible. I also got two CVEs in FreeRDP. Another obvious type of edge case is crashes. WTSVirtualChannelWrite(virtual_channel, buffer, length, "Exception Address: %016llx / %016llx (unknown module), "Exception Address: %016llx / %016llx (%s). If WinAFL refuses torun, try running it inthe debug mode. This article will not explain the Remote Desktop Protocol in depth. By fuzzing these 59 harnesses, WINNIE successfully found 61 bugs from 32 binaries. Note that you need a 64-bit winafl.dll build if In order to do that, I modified WinAFL to add a new option: -log_signal. Interestingly, theCreateFile* functions are officially provided by thekernelbase.dll library. Check a simple harness here: https://github.com/googleprojectzero/Jackalope/blob/6d92931b2cf614699e2a023254d5ee7e20f6e34b/test.cpp#L41 The no-loop mode lets the program loop by its own, just like in-app persistence. Additionally, this mode is considered as experimental since we have experienced some problems with stability and performance. Then I restart theprogram andsee that thetwo arguments are thepaths tomy test file anda temporary file. This function is a virtual extension that can be used to protect per-session data in the virtual channel client DLL. However, manually sending the malicious PDU again does not do anything we are unable to reproduce the bug. Oops By design, Microsoft RDP prevents a client from connecting from the same machine, both at server level and client level. WinAFL's custom_net_fuzzer.dll allows winAFL to perform network-based applications fuzzing that receive and parse network data. This can be done by patching the function write_to_testcase. As a drawback, DynamoRIO will add some overhead, but execution speed will still be decent. rewritten between target function runs. Send a new Format PDU with k < n formats: the format list is freed and reconstructed. Well, Im not sure myself it is not documented (at least at the time I am writing this article). Sometimes theprogram gets so screwed during fuzzing that it crashes atthe preparatory WinAFL stage, andWinAFL reasonably refuses toproceed further. Although WinAFL can beapplied toprograms that use other input methods, theeasiest way isto choose atarget that uses files as input. Fortunately, WinAFL can beeasily compiled onany machine. Concretely, we only lack two elements to start fuzzing: A good lead is to start by reading Microsofts specification (e.g. The virtual machines RAM would very quickly fill up, until at some point having to start filling up swap. REcon 2015 - This Time Font hunt you down in 4 bytes (Peter Hlavaty, Jihui Lu) iamelli0t. Network pentesting at the data link layer, Spying penguin. 56 0. By default, WinAFL writes mutations to a file. However, if there is only the binary program and no source code available, then standard afl-fuzz -n (non-instrumented mode) is not effective. the module containing functions you want tofuzz must not becompiled statically. This is a critical fact we must take into account for when we are fuzzing later! Of course, this is specific to RDPSND and such patches should happen in each channel. I modified my VC Server to integrate a slow mode. If nothing happens, download Xcode and try again. In this method, we directly deliver sample into process memory. Otherwise, WinAFL would instrument numerous library functions. Over the last few years, we have reported various issues to Microsoft in various Windows components including GDI+ and have received CVEs for them. The DLL should export the following two functions: We have implemented two sample DLLs for network-based applications fuzzing that you can customize for your own purposes. Figure 4. The Remote Desktop Protocol (RDP) is a proprietary protocol designed by Microsoft which allows the user of an RDP Client software to connect to a remote computer over the network with a graphical interface. In this case, just reverse to understand the root cause, analyze risk, and maybe grow the crash into a bigger vulnerability. In this section, I will present some of my results in a few channels that I tried to fuzz. And thefirst minutes offuzzing bring first crashes! The following cmake configuration options are supported: -DDynamoRIO_DIR=..\path\to\DynamoRIO\cmake - Needed to build the For more info about the original project, We thought they achieved encouraging results that deserved to be prolonged and improved. There is a second DLL custom_winafl_server.dll that allows winAFL to act as a server and perform fuzzing of client-based applications. This needs to happen within the target function so To avoid this, replace the SO_REUSEADDR option by SO_LINGER option in the server source code if available. Thanksfully, the PDB symbols are enough to identify most of the channel handlers. As said above, thefunction selected for fuzzing shouldnt have side effects. Introduction II. It uses thedetected syntax units togenerate new cases for fuzzing. Homemade keylogger. 2021 10.13089/JKIISC.2021.31.5.911 Keywords: Regression bug, Fuzz Testing, Directed fuzzing, Differential Fuzzing, Hybrid fuzzing. Reverse engineering will focus on the latter, as it holds most of the RDP logic. We can convert such a log into the Mod+Offset format that Lighthouse can read to visualize code coverage. Based onthe CFile::Open prototypes from theMSDN documentation, thea1 anda2 variables are file paths. I wait until thefunction execution iscompleted andsee that my test file isstill encrypted, while thetemporary file isstill empty. I set breakpoints atits beginning andend toexamine its arguments andunderstand what happens tothem by theend ofits execution. . You signed in with another tab or window. So, ifyour target doesnt meet theabove criteria, you can still adapt it toWinAFL ifyou want to. I debugged the TermService svchost process and stepped until ending up inside rdpcorets.dll. Attempt at RDP loopback connection. Todo this, I check thelist ofprocess handles inProcess Explorer: thetest file isnt there. I feel like attitude plays a great role in fuzzing. But ifyou pay attention tothe arguments, youll realize that thetarget wants toopen some ofits service files, not thetest file. We introduced in-memory fuzzing method to fuzz without sever agent. []. The answer lies in the Server Audio Formats and Version PDU. documents. The stability metric measures the consistency of observed traces. Indeed, each PDU sub-handler (logic for a certain message type) calls the CheckClipboardStateTable function prior to anything else. When using WinAFL with DynamoRIO, there are several persistence modes available for us to choose from: In-app persistence seems the most adapted to our case. Depending on how much available RAM there is left on the client, you cannot just send a PDU with 0xFFFFFFFF as clipDataId. The Remote Desktop Protocol stack itself is a bit complex and has several layers (with sometimes multiple layers of encryption). There also exist alternate implementations of RDP, like the open-source FreeRDP. We have just talked about how DynamoRIO monitors code coverage; it starts monitoring it when entering the target function, and stops on return. The first one can find interesting bugs, but which sometimes are very hard to analyze. The following is a description of how . If you are using shared memory for sample delivery then you need to make sure that in your harness you specifically read data from shared memory instead of file. In practice, this . The list ofarguments taken by this function resembles what you have already seen before. Dont forget todisable thedebug mode! If guessing wont work, another possibility is to capture code coverage at the moment we send a PDU over the target virtual channel. arky, Tekirda ilinin bir ilesi. Now lets do some fuzzing! Upgrading to 8 GB of RAM solved the issue, meaning the memory overcommitment was not as violent as in the CLIPRDR bug. Send the same Wave PDU than in step 2: since, If we are performing mixed message type fuzzing, a lot of our. Obviously, its less impressive on a client than on a server, but its still nastier than your usual mere crash. Imagine a Windows machine that hosts several critical services, and from which you can connect to another machine through RDP since the DOS hangs the entire system, these critical services would be impacted too. WinAFL is doing in-memory fuzzing which means that we don't have to start the application every time, but let's forget this for now so that our discussion does not get too complicated. WinAFL Fuzzing AFL is a popular fuzzing tool for coverage-guided fuzzing. Background: In our previous research, we used WinAFL to fuzz user-space applications running on Windows, and found over 50 vulnerabilities in Adobe Reader and Microsoft Edge.. For our next challenge, we decided to go after something bigger: fuzzing the Windows kernel. To see the supported instrumentation flags, please refer to the documentation Until current research about RDP fuzzing, server agent was used to send back fuzzing input. This option can be used to fuzz processes that cannot be directly launched by WinAFL, such as system services. For instance, if you notice the message type has a field which is an array of dynamic length, and that this length is coded inside another field and does not seem to match the actual number of elements in the array, maybe its an out-of-bounds bug about improper length checking. the target process is killed and restarted. AFL was developed tofuzz programs that parse files. ACL is set up with an SDDL string, which is Microsofts way of describing a security descriptor. Note that inIDA, thefile path ispassed tothe CFile::Open function as thesecond argument because thiscall isused. Return normally (So that WinAFL can "catch" this return and redirect What is coverage-guided fuzzing ? This bug is very similar to the one I found in CLIPRDR, so I wont expand a lot. The harness is also essential to avoid edge cases. // Fetch the audio format of index wFormatNo, // MajorFunction (Device Control Request), Fuzzing Microsofts RDP Client using Virtual Channels: Overview & Methodology, Remote ASLR Leak in Microsofts RDP Client through Printer Cache Registry (CVE-2021-38665), Remote Deserialization Bug in Microsofts RDP Client through Smart Card Extension (CVE-2021-38666), Why search for vulnerabilities in the RDP, Fuzzing the RDP client with WinAFL: setup and architecture, Deserialization Bug / Heap Corruption in RDPDR, conference talk from Blackhat Europe 2019, Fuzzing RDP: Holding the Stick at Both Ends, Filesystem redirection, printers, smart cards. Fuzzing process with WinAFL in "no-loop" mode. Using Android to keep tabs on your girlfriend. It is opened by default. In summary, we make the following contributions: We identified the major challenges of fuzzing closed-source Windows applications; In summary, we make the following contributions: We identied the major challenges of fuzzing closed-source Windows applications; Time toexamine contents ofthese files. Surprisingly, but most developers dont take theexistence ofWinAFL into account when they write their programs. location of your DynamoRIO cmake files (either full path or relative to the Please run the to send test cases over network). This requires patching winsta.dll to activate g_bDebugSpew: With some help, we eventually managed to identify the endpoint of the RPC call, in termsrv.dll. Download andinstall Visual Studio 2019 Community Edition (when installing, select Develop classic C++ applications. This method brings two advantages. I spent a lot of time on this issue because I had no idea where the opening could fail. Once the channel is closed, we cant send PDUs anymore. I eventually switched to deterministic and noticed it usually happened around 5 minutes of fuzzing. create two users on the same virtual machine, User1 and User2; setup the RDP server with RDPWrap to allow remote connection for User1; use the RDP client on a User2 session, by connecting to 127.0.0.2 with the credentials of User1.
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