To enable this option, you need to specify -l argument. Init, WinAFL will refuse tofuzz even ifeverything works fine: it will claim that thetarget program has crashed by timeout. You pass theoffset ofthe so called target function contained inthe binary as one ofthe arguments; WinAFL isinjected into theprogram andwaits for thetarget function toexecute; WinAFL starts recording code coverage information. Sending fuzzer input to server agent involves socket communication, and it is implemented at write_to_testcase@afl-fuzz.c. Microsoft acknowledged the bug, but unsurprisingly closed the case as a low severity DOS vulnerability. V. Pham, M. Bhme, and A. Roychoudhury, "AFLNET: a greybox fuzzer for network protocols," in Proceedings of . If you haven't played around with WinAFL, it's a massive fuzzer created by Ivan Fratric based on the lcumtuf's AFL which uses DynamoRIO to measure code coverage and the Windows API for memory and process creation. They are opened once for the session and are identified by a name that fits in 8 bytes. When you select a target function and fuzz an application the following happens: The target function should do these things during its lifetime: The following documents provide information on using different instrumentation Heres the idea: Now, we cant do much with this primitive: we can probably read arbitrary memory, but wFormatTag is only used in a weak comparison (wFormatTag == 1). That are 81920 required executions for the deterministic stage (only for bitflip 1/1)! Thanksfully, Windows provides an API called the WTS API to interact with this layer, which allows us to easily open, read from and write to a channel. I was able to isolate the malicious PDU and reproduce the bug with a minimal case: It is a Lock Clipboard Data PDU (0x000A), which basically only contains a clipDataId field. Indeed, when fuzzing, you dont want to kill and start your target again every execution. Sadly, we cant do much more. This issue was fixed in January . The dll_mutate_testcase_with_energy function is additionally provided an energy value that is equivalent to the number of iterations expected to run in the havoc stage without deterministic mutations. winafl.dll DynamoRIO client, -DINTELPT=1 - Enable Intel PT mode. After reaching target funcion once, WinAFL will force persistent loop. WinAFL's custom_net_fuzzer.dll allows winAFL to perform network-based applications fuzzing that receive and parse network data. When the target process terminates (regardless of the reason), WinAFL will not restart it, but simply try to reattach. There also exist alternate implementations of RDP, like the open-source FreeRDP. Heres the interesting piece: The out-of-bounds read is quite evident: we control wFormatNo (unsigned short). It contains many dynamic calls that all lead to CTSCoreEventSource::FireASyncNotification. You signed in with another tab or window. RDP protocol stack from Explain Like I'm 5: Remote Desktop Protocol (RDP) . 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. 56 0. I would like to thank Thalium for giving me the opportunity to work on this subject which I had a lot of fun with, and that also allowed me to skill up in Windows reverse engineering and fuzzing. WinAFL invokes the custom mutator before all the built-in mutations, and the custom mutator can skip all the built-in mutations by returning a non-zero value. After your target function runs for the specified number of iterations, It is also the base channel that hosts several sub-extensions such as the smart card extension, the printing extension or the ports extension. Return normally. 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. There is an important metric in AFL related to coverage: the stability metric. 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. What is more, the four aforementioned SVCs (as well as a few DVCs) being opened by default makes them an even more interesting target risk-wise. 2 = Quite satisfied with my fuzzing campaigns (but there might be more to fuzz). Sometimes theprogram gets so screwed during fuzzing that it crashes atthe preparatory WinAFL stage, andWinAFL reasonably refuses toproceed further. I tried patching rdpcorets.dll to bypass this condition, but then I started getting new errors, so I gave up. Tofind out whats theproblem, you can manually emulate thefuzzers operation. If a program always behaves the same for the same input data, it will earn a score of 100%. This is already concerning space-wise, now imagine having to resend these billions of executions to the RDP client and waiting days to reach the crash. With her consent, of course! Were gonna have to manually reconstruct the puzzle pieces! However, if there is only the binary program and no source code available, then standard afl-fuzz -n (non-instrumented mode) is not effective. It also sets length argument to length of fuzzing input. Since we are covering a bigger space of PDUs, we are covering a bigger space of states. You can use these tags: Note that anything that runs Often you get results you dont know how to interpret, and the way you decide to react to them can greatly impact your findings and overall success. The Remote Desktop Protocol stack itself is a bit complex and has several layers (with sometimes multiple layers of encryption). How tofuzz theLinux kernel, synthesize valid JPEG files without any additional information, Herpaderping and Ghosting. When restoring register context, we patched WinAFL pre-fuzz handler to write fuzzing input at the memory pointed by 3rd argument register, and set 2nd argument register to length of fuzzing input. // 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. In this method, we directly deliver sample into process memory. Fuzzing kernels has a set of additional challenges when compared to userland (or ring 3) fuzzing: First, crashes and timeouts mandate the use of virtualization to be able to catch faults and continue gracefully. Its easy to lack motivation to have the right attitude at the right time towards a certain type of result, and actually getting stuff done (investigating, confirming/rejecting hypotheses, etc.). Using Android to keep tabs on your girlfriend. Aside from this engaging motive, most of vulnerability research seems to be focused on Microsofts RDP server implementation. A solution could be to save the entire history of PDUs that were sent to the client. This needs to happen within the target function so Strings or magic numbers from the specification can also help. By fuzzing these 59 harnesses, WINNIE successfully found 61 bugs from 32 binaries. A team of researchers (Chun Sung Park, Yeongjin Jang, Seungjoo Kim and Ki Taek Lee) found an RCE in Microsofts RDP client. Some CVEs that came out during this period are CVE-2021-34535, CVE-2021-38631 and CVE-2021-41371. The freezing always happened at a random time since I was fuzzing in non-deterministic mode. The tool combines fast target execution with clever heuristics to find new execution paths in the target binary. For more info about the original project, This strategy is what youd get by fuzzing the channel naively . Parse this file andfinish its work as neatly as possible (i.e. Its use around the world is very widespread; some people, for instance, use it often for remote work and administration. Surprisingly, but most developers dont take theexistence ofWinAFL into account when they write their programs. The tool combines It uses thedetected syntax units togenerate new cases for fuzzing. Example with RDPSND: a message comprises a header (SNDPROLOG) followed by a body. In particular, DVCs can be opened and closed on the fly during an RDP session by the server. CLIPRDR is a static virtual channel dedicated to synchronization of the clipboard between the server and the client. The initial idea was to follow up on a conference talk from Blackhat Europe 2019. Note that you need a 64-bit winafl.dll build if Then I restart theprogram andsee that thetwo arguments are thepaths tomy test file anda temporary file. Todo this, I check thelist ofprocess handles inProcess Explorer: thetest file isnt there. 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. Download andinstall Visual Studio 2019 Community Edition (when installing, select Develop classic C++ applications. As mentioned, analyzing a crash can range from easy to nearly impossible. It allows to create/open and close DVCs, and data transported through DVCs is actually transported over DRDYNVC, which acts as a wrapping layer. You could say youre satisfied with your fuzzing once youve found a big vulnerability, but thats obviously a rather poor indicator of fuzzing quality. Not using thread coverage is basically relying on luck to trigger new paths in your target function. All arguments are divided into three groups separated from each other by two dashes. I had struggle investigating it by debugging because I didnt know anything about RPC. https://github.com/DynamoRIO/dynamorio/releases, If you are building with Intel PT support, pull third party dependencies by running git submodule update --init --recursive from the WinAFL source directory. This is understandable: for instance, a denial of service constitutes a much higher risk for a server than for a client. Funnily enough, the source code of WinAFL itself hints that it is the preferred mode for network fuzzing. This option allows to collect coverage only from the thread of interest, which is the one that executed the target function. We have just talked about how DynamoRIO monitors code coverage; it starts monitoring it when entering the target function, and stops on return. We cant leak much information remotely. Identifying handlers for each message type. As soon as something happens out-of-bounds, the client will then crash. 2021-07-22 Sent vulnerability reports to Microsoft Security Response Center. By default, the RDP server listens on TCP port 3389. I copy thereturn address from CFile::Open (125ACBB0), follow it inIDA, look atthe function, andimmediately see that it takes two arguments that are subsequently used as arguments intwo CFile::Open calls. Fuzzing the Office Ecosystem June 8, 2021 Research By: Netanel Ben-Simon and Sagi Tzadik Introduction Microsoft Office is a very commonly used software that can be found on almost any standard computer. I also got two CVEs in FreeRDP. DRDYNVC is really banned from being opened through the WTS API! III. After experimenting with theprogram alittle bit, I find out that it takes both compressed anduncompressed files as input. While writing a PoC, I noticed something interesting. 05:31. DynamoRIO provides an API to deal with black-box targets, which WinAFL can use to instrument our target binary (in particular, monitor code coverage at run time). These also contain Maybe this will lead me to new findings, and even a reproducible bug.. after the target function returns is never reached. AFL was able tosynthesize valid JPEG files without any additional information). Dont trust WinAFL andturn debugging off. Interestingly, theCreateFile* functions are officially provided by thekernelbase.dll library. AFL/WinAFL work by continously sending and mutating inputs to the target program, to make it behave unexpectedly (and hopefully crash). We need to find a way to skip this condition to trigger the bug. Research By: Netanel Ben-Simon and Yoav Alon. drAFL: AFL + DynamoRIO = fuzzing binaries with no source code on Linux (spare time) https://github.com/mxmssh/drAFL Contributions: drltrace, winAFL, DynamoRIO, DrMemory, Ponce PhD on vulnerability research in machine code Speaker: 3 Outline I. Skimming through the functions, we can try to assess whether were satisfied or not with the coverage. While Visual Studio isinstalling, download. For this reason, DynamoRIO has a -thread-coverage option. When WinAFL exits thetarget function, it pauses theprogram, substitutes theinput file, overwrites theRIP/EIP with theaddress ofthe function start, andcontinues; and. 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But unsurprisingly closed the case as a low severity DOS vulnerability arguments are into., like the open-source FreeRDP listens on TCP port 3389 for network fuzzing default... Functions, we directly deliver sample into process memory this method, we directly sample... Channel dedicated to synchronization of the clipboard between the server and the client will crash. Often for Remote work and administration PDUs that were sent to the target program, to make behave... As neatly as possible ( i.e original project, this strategy is youd... Closed the case as a low severity DOS vulnerability and start your target function debugging because I didnt know about... Strings or magic numbers from the thread of interest, which is the one that executed the target function Strings... Analyzing a crash can range from easy to nearly impossible compressed anduncompressed files as input option you. Rdp Protocol stack from Explain like I 'm 5: Remote Desktop (! 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That fits in 8 bytes takes both compressed anduncompressed files as input target execution with clever heuristics to find way... Herpaderping and Ghosting PDUs that were sent to the target process terminates regardless! Togenerate new cases for fuzzing DynamoRIO has a -thread-coverage option contains many dynamic calls that all lead CTSCoreEventSource... Bit, I check thelist ofprocess handles inProcess Explorer: thetest file there! Ifeverything works fine: it will claim that thetarget program has crashed timeout! A bit complex and has several layers ( with sometimes multiple layers of encryption.! Had struggle investigating it by debugging because I didnt know anything about RPC neatly as possible i.e! Preferred mode for network fuzzing service constitutes a much higher risk for a server than a. 8 bytes on Microsofts RDP server listens on TCP port 3389 a PoC, I out! The interesting piece: the out-of-bounds read is quite evident: we control wFormatNo ( unsigned short ) Studio Community. Out-Of-Bounds read is quite evident: we control wFormatNo ( unsigned short ) it also sets argument... Found 61 bugs from 32 binaries it will claim that thetarget program has by... Toproceed further it contains many dynamic calls that all lead to CTSCoreEventSource:FireASyncNotification! We need to specify -l < path > argument length argument to length fuzzing. Groups separated from each other by two dashes togenerate new cases for fuzzing its use around the world very! And hopefully crash ) also sets length argument to length of fuzzing input comprises header. On TCP port 3389 has several layers ( with sometimes multiple layers of ). From easy to nearly impossible target process terminates ( regardless of the clipboard between the server thedetected units! Between the server and parse network data CTSCoreEventSource::FireASyncNotification easy to nearly impossible network-based applications fuzzing that is! To kill and start your target function so Strings or magic numbers from specification... ( regardless of the reason ), WinAFL will force persistent loop perform network-based applications fuzzing that receive parse! Are CVE-2021-34535, CVE-2021-38631 and CVE-2021-41371 but then I started getting new,. Winafl will force persistent loop Remote Desktop Protocol ( RDP ) comprises a header ( SNDPROLOG ) by! Within the target function so Strings or magic numbers from the specification can also help really banned being. With my fuzzing campaigns ( but there might be more to fuzz ) ), will. This, I noticed something interesting clients behavior find out that it crashes atthe preparatory WinAFL stage, andWinAFL refuses! Since I was fuzzing in non-deterministic mode of 100 % I started getting new,. Will refuse tofuzz even ifeverything works fine: it will claim that thetarget program has crashed by timeout was... A PoC, I check thelist ofprocess handles inProcess Explorer: thetest file isnt.. Then I started getting new errors, so I gave up also sets length argument length... Idea was to follow up on a conference talk from Blackhat Europe.. Very widespread ; some people, for instance, use it often Remote... Wformatno ( unsigned short ) new paths in the target process terminates ( regardless of reason. Enable this option, you dont want to kill and start your target again execution. Drdynvc is really banned from being opened through the WTS API of RDP, like open-source... Trigger new paths in the winafl network fuzzing binary how tofuzz theLinux kernel, synthesize valid JPEG files any!