Dave Maynor’s got me thinking. And today, after some inspiring presentations at TechEd last week, I took the time to do some testing. Set the appropriate bit (0x4000) in the DLL Characteristics field of the PE header, and you turn on ASLR for your program of choice. So clearing the bit will disable ASLR, but will Windows File Protection prevent you from changing the program? I didn’t think it would, because you’re only touching the PE Header, which is not protected by the Authenticode signature. Turns out it does work: you can disable ASLR for a given program, like Internet Explorer.
And WFP will not restore the file. But for another reason than I thought: with Vista, WFP is actually called. And it works differently: files are protected by Security Descriptors, and are not replaced automatically when deleted or modified. So the neat trick of deleting a system-file in Windows XP (like utilman.exe) only to see it reappear a couple of seconds later,. Change the Security Descriptor of the file in Vista (taking ownership and giving you delete rights), delete the file, and it’s gone. No more resurrection. If you want to play with the ASLR toggle, you can use to edit the PE Header and to test it.
So why would you disable ASLR? I don’t know, I just think it’s a funny trick 😉. But maybe you got an idea?
Let me know, post a comment.
Michael Howard, Matt Miller, John Lambert and Matt Thomlinson Microsoft Corporation December 2010 Introduction Starting with Windows XP SP2 and Windows Server 2003, Microsoft Windows offers a number of defensive enhancements designed to protect customers. Applications that run on these platforms should take full advantage of these defenses. They are essentially free, and can transform a serious vulnerability into a crashing bug that protects customers from more serious forms of exploitation. In the case of Internet Explorer, some of the Windows Vista defenses only come into play when all components consumed by the browser support the defenses. Because browsers are one of the most attacked (and compromised) software components, it is important that popular components consumed by the browser take full advantage of these defenses. The purpose of this short paper is to detail the defenses, and explain how software vendors should take advantage of the defenses to protect our shared customers In the case of Internet Explorer, some Windows defenses only come into play when all browser components support those defenses.
Sep 21, 2010 Darmowe 16 Lekcji Video. Intuicyjne wprowadzenie i formalna definicja granic funkcji Heine'go. More Granice Funkcji Etrapez images. Granice funkcji etrapez. View rzdl7 from MH THYROID at Akademia Ekonomiczna w Krakowie. KURS GRANICE Lekcja 7 Wzory na granice funkcji. Odpowiedzi do zadania domowego www.etrapez. Download >> Download Granice funkcji etrapez pdf Read Online >> Read Online Granice funkcji etrapez pdf granice ciagow twierdzenia e do nieskonczonosci wzory granice.
Popular browser components should take full advantage of these defenses because browser applications are among the most frequently targeted for attack. The purpose of this paper is to detail the available defenses and to explain how software vendors can take advantage of these defenses to protect our shared customers. The Many Buffer Overrun Defenses in Microsoft Windows and Visual C Windows incorporates a number of defensive strategies to protect customers from attack. Some of these defenses are part of the core operating system, and additional defenses are offered by the Microsoft Visual C compiler. The defenses include:. /GS Stack buffer overrun detection.
/SafeSEH exception handling protection. Structured Exception Handler Overwrite Protection (SEHOP). Data Execution Prevention (DEP) / No eXecute (NX). Address space layout randomization (ASLR).
Pointer Encoding. Heap corruption detection. Migration of buffer-overrun prone functions to safer versions.
On the following pages you’ll find explanations of each of these defenses, as well as information about how to enable them and how to verify that your application is actually taking advantage of them. /GS Stack Buffer Overrun Detection The Stack Buffer Overrun Detection capability was introduced to the C/C compiler in Visual Studio.NET 2002 and has been updated in subsequent versions. /GS is a compiler switch that instructs the compiler to add startup code, and function epilog and prolog code, to generate and check a random number that is placed in a function's stack. If this value is corrupted, a handler function is called to terminate the application and thus reduce the chance that the shell code attempting to exploit a buffer overrun will execute correctly. The Stack Buffer Overrun Detection capability was introduced to the C/C compiler in Visual Studio.NET 2002 and has been updated in subsequent versions. /GS is a compiler switch that instructs the compiler to add startup code, and function epilog and prolog code, to generate and check a random number that is placed in a function's stack.
If this value is corrupted, a handler function is called to terminate the application and thus reduce the chance that the shell code attempting to exploit a buffer overrun will execute correctly. Note The performance impact of /GS is difficult to measure because it is highly dependent on coding style. Code with large numbers of stack-based string buffers and arguments might see a small impact; code with without them will see no impact.
A ball-park figure may be on the order of a 3 percent performance impact, which is partially offset through other optimizations in later versions of the compiler. Note that Visual C 2005 (and later) also reorders data on the stack to make it harder to predictably corrupt that data. Examples include:.
Moving buffers to higher memory than non-buffers. This step can help protect function pointers that reside on the stack. Moving pointer and buffer arguments to lower memory at run time to mitigate various buffer overrun attacks. Visual C 2010 includes enhancements to /GS which expand the heuristics used to determine when /GS should be enabled for a function, and when /GS can safely be optimized away.
In order to take advantage of enhanced /GS heuristics, ISVs using Visual C 2005 SP1 or later should add the following instruction in a commonly used header file to increase the number of functions protected by /GS. #pragma strictgscheck(on) What’s the difference between –GS in Visual C 2010 and strictgscheck? The rules for determining which functions require /GS protections are more aggressive in Visual C 2010 than they are in the compiler's earlier versions; however, the strictgscheck rules are even more aggressive than Visual C 2010.
Even though Visual C2010 strikes a good balance, strictgscheck should be used for Internet-facing products. ISV Tasks. ISVs should compile their code with the most recent version of the compiler. At the time of writing, this version is VC 2010 (cl.exe version 16.00). ISVs using versions of VC older than VC 2010 should add #pragma stringgscheck(on) to a common header file. ISVs using VC 2010 and later should add #pragma stringgscheck(on) to Internet-facing products.
ISVs should compile with the /GS flag. ISVs should link with libraries that use /GS. /SafeSEH Exception Handling Protection An exception handler is a unit of code executed when an exceptional condition, such as a divide-by-zero, occurs. The address of the handler is held on the stack frame of the function and is therefore subject to corruption and hijacking if a buffer overflow allows an attacker to overwrite the stack. The linker included with Visual Studio 2003 (and later versions) includes an option to store the list of valid exception handlers in the image's PE header at compile time.
When an exception is raised at run time, the operating system (Windows Server 2008 R2, Windows 7, Windows Server 2008, Windows Vista, Windows Server 2003, or Windows XP with Service Pack 2 or 3) will not dispatch to an address in that image unless it is one of the exception handler addresses in the PE header. Performance: There is no performance impact of /SAFESEH in the non-exception code path. ISV Tasks. ISVs should link their images with /SAFESEH. ISVs should link with libraries that are also linked with /SAFESEH. Structured Exception Handler Overwrite Protection (SEHOP) In Windows Vista SP1 and Windows Server 2008, Microsoft introduced support for Structured Exception Handler Overwrite Protection (SEHOP).
SEHOP is capable of protecting against exception chain corruption without requiring code to be rebuilt, unlike /SAFESEH, which requires a re-link. SEHOP support was extended in Windows 7 and Windows Server 2008 R2 by permitting applications to opt-in on a per application basis, as opposed to enabling or disabling SEHOP for the entire system. By default, SEHOP is disabled on Windows Vista and Windows 7 for compatibility reasons, and it is enabled by default on Windows Server 2008 and Windows Server 2008 R2. SEHOP can be enabled for an application on Windows 7 by applying the registry setting. Substitute the name of your main EXE for MyExecutable.exe in the example below. HKEYLOCALMACHINE SOFTWARE Microsoft Windows NT CurrentVersion Image File Execution Options MyExecutable.exe 'DisableExceptionChainValidation'=dword:00000000 When using a 64-bit version of Windows, set the Image File Execution Options registry key under the Wow6432Node portion of the registry that corresponds to the registry hive used by 32-bit applications (e.g. HKLM Software Wow6432Node.): ISV Tasks.
ISVs should opt-in their applications to SEHOP on Windows 7 and later. What’s the difference between SAFESEH and SEHOP? On the surface, SAFESEH and SEHOP, appear the same: both help mitigate the severity of attacks that attempt to overwrite exception handlers. SEHOP is a more complete defense because it can protect against handlers that point to non-SafeSEH modules and handlers that point to a non-image region, such as the heap. Either SafeSEH or SEHOP can be used, but the latter is preferred. The best solution is to build your code to use both: SafeSEH will work on versions of Windows prior to Windows Vista SP1, and SEHOP provides a more comprehensive defense on Windows Vista SP1 and later.
Data Execution Prevention (DEP) / No eXecute (NX) Named DEP by Microsoft, and NX by AMD, this defensive technology requires CPU support that prevents code from executing in data segments. Most modern Intel CPUs now support this capability, and all current AMD CPUs support NX.
DEP support was first introduced in Windows XP SP2, and is a critically important defense in Windows when used with ASLR. The relationship between DEP/NX and ASLR is explained below. If an application targets Windows XP SP3, then ISVs should call SetProcessDEPPolicy to enforce DEP/NX. If it is unknown whether the application will run on a down-level platform that includes support for SetProcessDEPPolicy or not, then call the following code early in the startup code. FUNCPTR fp = (FUNCPTR)EncodePointer(&SomeFunc;); // more code (.(FUNCPTR)DecodePointer(fp)); Performance There is negligible performance impact as the encode and decode operations are often optimized to an inline XOR operation. ISV Tasks.
ISVs should encode globally-scoped function pointers. ISVs should consider encoding all function pointers.
Heap Metadata Protection Heap metadata protection is the ability to cause an application to fail immediately if the heap manager detects that the application has corrupted the heap, or if the heap becomes inconsistent. Heap metadata protection not only detects heap-based buffer overruns, but also certain illegal operations. (For example, freeing a pointer to the wrong heap will also fail the application.) Enabling heap metadata protection requires a small code addition.
If the application targets Windows Vista and later or Windows Server 2008 and later, add this line to main or WinMain. Defense Priority Where Defense is Made SDL Type C Compiler Version Critical N/A Requirement Address space layout randomization opt-in Critical Link time Requirement DEP opt-in Critical Link time Requirement /GS stack-based buffer overrun detection Critical Compile time Requirement /SAFESEH exception handler protection Critical Link time Requirement Function migration High Code change Removal of is an SDL requirement, automated migration to safer versions is recommended. SEHOP opt-in High Setup Future SDL release requirement Pointer Encoding Moderate Code change Recommendation Heap corruption detection Moderate Code change Requirement Important Note: It is critically important for software developers who are building Internet Explorer extensions and plugins to opt in for ASLR and DEP and take advantage of the defenses in Internet Explorer 8 and later. Developers who are using agile development methods can add critical defenses in the next full sprint cycle (and others in a subsequent sprint). How to Verify Compliance with this Paper The following practices should be verified using the.
C Compiler version. Use of /GS.
Use of /SAFESEH. Use of /NXCOMPAT (DEP). Use of /DYNAMICBASE (ASLR). Ensure BinScope is configured to check for the settings above.
A ‘PASS’ for each check indicates that the code has the settings enabled. Note: Presently, BinScope checks for VC 2005 or later. Use of VC 2008 SP1 or later is highly recommended because of improvements in -GS. Important: In some cases, DEP may not be enforced for the application or component. This issue is often caused when the application is linked to a non-DEP enabled library (for example, older versions of the Abstract Template Library (ATL) included with Visual Studio). If ATL is required by the application, use the version shipped with Visual Studio 2005 (ATL v8.0) or later. The ATL version can be verified with a debug code like the one below, which can be added to the main or WinMain function.
// Version in Visual Studio 2005 or later assert(AtlGetVersion(NULL) = 0x0800); How to Verify Compliance with Function Migration Developers can look for the two #defines described earlier to verify that the C compiler code is configured to migrate some C runtime functions to safer calls. How to Verify Compliance with SEHOP Applications that run on Windows 7 can check compliance with SEHOP by verifying that the appropriate registry values have been set.
Specifically, the “DisableExceptionChainValidation” in “HKEYLOCALMACHINE Software Wow6432Node Microsoft Windows NT CurrentVersion Image File Execution Options ” should be set to 0. Use the following PowerShell script to determine if SEHOP is enabled for an application.
Get-sehop How to Verify Compliance with Pointer Encoding The best way to verify compliance with Pointer Encoding is to look for the calls to EncodePointer or EncodeSystemPointer in the code accessing function pointers. How to Verify Compliance with Heap Metadata Protection The best way to verify compliance with Heap Metadata Protection is to look for the correct call to HeapSetInformation in the code, or to compile with Visual C 2010 or later.
Summary Microsoft has added many buffer overrun defenses to Windows and Visual C. Software developers who are building on Windows have the responsibility of adding these defenses to protect our shared customers. This is especially true for software developers who build extensions or controls for browsers such as Internet Explorer.
By following the guidance offered in this paper, software developers can build components that operate more securely on Windows and within Internet Explorer. References. DEP as a mitigation technology ( and ).
if you navigate to a Website and your browser crashes, will you go back to that site another 255 times Actually, I was going to reply back saying that while.I. wouldn’t go, you’d only have to convince another 255 people to go there instead.
But then I did some calculations Botnets today of 10,000 computers are not uncommon (even 100,000 computers). With only a 1:256 chance of infecting a computer, that reduces my botnet to only 40 (or 400) computers. And given that most botnets grow using the infected computers as a launching point, with only 40 computers in my botnet, growing it to just 400 will be quite difficult.
So yeah, I agree that 1:256 is probably enough – at least in the initial version! I imagine there plenty more up your sleeves for version 2.0 🙂. I wrote to experts-exchange about this paper and they referred me to your blog, which I joined. I am glad that the research was incomplete and that Microsoft had not ignored, but actually improved upon what the reseacher reported. I realize that the following is only tangentially related to security, but your blog gives me the opening. Perhaps you can redirect me to the correct person to answer this innane question regarding naming conventions, if there are any relating to this particular file. I have a question about how Microsoft comes up with names.
In this case there is no indication that the MountPoint name is a Microsoft product. This name caused my security scanning software and me unnecessary problems. I spent the last three days and nights researching a potential problem that was flagged by the AVG Anti-Malware 7.5 software.
It is a folder known as: C:System Information FolderMountPointManagerRemoteDatabase. AVG provided a warning flag, but no capability to remove or quarantine it. I used Google to try to find out what this was and most identified it as a Root Kit. Worrisome to say the least because this is the first time that anything got through my defenses. In desperation, I finally called Microsoft security.
They told me that this folder and MountPoint were part of the operating system relating to disk management. A big sigh and a refreshing sleep. I immediatly wrote to AVG and asked them to remove this from their potential bad things file. False positives can cause agony! Can you ‘splain to me how this name was selected and are there any other names which one would never think to be part of a that one should be concerned about triggering a response from one of my many scanners?
Enable Aslr On Windows10
Kidding about the other names curious on how these non Microsoft names are created. Sincerely, Michael. When I first heard of this particular implimentation, I was strucken with a few ways to potentially overcome this security implimentation. One way around this could simply be as easy as subtle misdirection of exception handling (ELF for example). Consider your 1/256 chance (1 byte of Rand), combine it with random string mechanisms that are checked against stack return events (why not just use crc md5/sha1 checks proc time maybe?), and we find there to be many similar potential points of 'failure' for any possable outcome anyway. All it takes is one way, and it’s only a matter of time and talent. A step in the right direction.