Vista heap

Windows Vista SP1, 7, 8, 8. Windows Vista, 7, 8, 8. In Windows Vista and in later operating systems, memory allocations are dynamic. Therefore, there is no limitation for memory allocation. However, if you allocate too much memory to the desktop heap, negative performance may occur. This is the reason why we do not recommend that you set a value that is over Note The desktop heap size is not affected by the physical RAM on the computer.

Therefore, you cannot improve the performance by adding physical RAM. For more information about similar issues, click the following article numbers to view the articles in the Microsoft Knowledge Base:. Check whether the problem is fixed. If the problem is fixed, you are finished with this section.

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For up to 6 people. Premium apps. Try 1 month free. Was this information helpful? Yes No. Thank you! Any more feedback? This section describes some of the noteworthy integrity checks that have been added. Previous versions of the Windows heap made use of catch-all exception handling blocks in certain cases where exceptions were considered non-fatal. This had the potential to make it easier for attackers to exploit heap corruption issues in certain cases, in particular by allowing an attacker multiple attack attempts.

Therefore, these catch-all blocks have been removed from the heap in Windows 8, meaning such exceptions now lead to safe termination of the application. The HEAP handle is an internal data structure that is used to maintain the state associated with a given heap.

Prior to Windows 8, an attacker could use a heap-based memory corruption vulnerability to coerce the heap into freeing the HEAP handle data structure. After doing this, the attacker could force the heap to reallocate the memory that previously stored the HEAP handle state. This in turn allowed an attacker to corrupt internal heap metadata, including certain function pointer fields.

The HEAP handle data structure includes a function pointer field called CommitRoutine that is called when memory regions within the heap are committed. Starting with Windows Vista, this field was encoded using a random value that was also stored as a field in the HEAP handle data structure. While this mitigated trivial corruption of only the CommitRoutine function pointer, it did not mitigate the case where an attacker could corrupt both the CommitRoutine and the field that stored the encoding key.

The Windows 8 heap mitigates this attack by using a global key to encode the CommitRoutine function pointer rather than a key that is stored within the HEAP handle data structure. In some cases, the Windows heap may flag an allocation as having an extended block header which informs the heap that there is additional metadata associated with the allocation.

In previous versions of Windows, an attacker could corrupt the header of an allocation and make it appear as if the allocation had an extended block header. This could then be used by an attacker to force the heap to free another allocation that is currently in use by the program.

The Windows 8 heap mitigates this attack by performing additional validation on extended block headers to ensure that they are correct. Some of the attacks that have been proposed by security researchers rely on reallocating memory that is already in use by the program e. If a block is flagged as in-use, the heap takes steps to safely terminate the process. One of the exploitation techniques proposed in [4] involved corrupting heap metadata FirstAllocationOffset and BlockStride that is used by the Low Fragmentation Heap LFH to calculate the address of an allocation within a subsegment.

By corrupting these fields, an attacker can trick the heap into returning an address that is outside the bounds of a subsegment and potentially enable corruption of other in-use heap allocations. The heap manager in Windows 8.

One of the ways that the Windows 8 heap better protects application data and heap metadata is through the use of guard pages. In this context, a guard page is an inaccessible page of memory that will cause an access violation if an application attempts to read from it or write to it.

Placing a guard page between certain types of sub-regions within the heap helps to partition the heap and localize any memory corruptions that may occur. In an ideal setting, the Windows heap would encapsulate all allocations in guard pages in a manner that is similar to full-page heap verification. Unfortunately, this type of protection is not feasible for performance reasons. Instead, the Windows 8 heap uses guard pages to isolate certain types of sub-regions within the heap.

In particular, guard pages are enabled for the following types of sub-regions:. Allocation order randomization. One of the behaviors that attackers rely on when exploiting heap buffer overruns is that there must be a way to reliably position certain heap allocations adjacent to one another. This requirement stems from the fact that an attacker needs to know how many bytes must be written in order to corrupt a target allocation on the heap while minimizing collateral damage to the heap that could cause the application and hence the attack to be terminated.

Attackers typically try to ensure that allocations are immediately adjacent to each other through techniques that are often referred to as heap massaging or heap normalization. How to read this table using the HEAP data structure overwrite technique as an example : The HEAP data structure overwrite technique is feasible on Windows Vista, Windows Server , and Windows 7 with a high degree of perceived difficulty due to the prerequisites required in order to make use of it.

The majority of the existing heap-based exploitation techniques that rely on the corruption of heap metadata cannot be used in their current form to exploit heap memory corruption vulnerabilities on Windows Vista and above.

This is due to the hardening changes that have been made to the heap manager such as removing commonly targeted data structures, protecting the integrity of heap metadata, and making the state of the heap non-deterministic. While new attacks have been proposed[13], we are not currently aware of any public exploits targeting Windows Vista and above that rely on heap metadata corruption to exploit a real-world heap memory corruption vulnerability.

With that said, we expect that heap-based exploitation techniques will continue to be an active research topic. As such, we will continue to investigate heap enhancements such as those included in RobustHeap that will make it more difficult for attackers to reliably exploit heap-based memory corruption vulnerabilities. Corrupted Heap Termination Redux. June, Jul, Third Generation Exploitation. Black Hat Windows Briefings Feb, Reliable Windows Heap Exploits.

Windows Heap Overflows. Black Hat USA. A new way to bypass Windows heap protections. Sep, Dec, Understanding and Bypassing Windows Heap Protection. Heaps About Heaps. SyScan Attacking the Vista Heap.