We saw in the PEB Data Structure many of the members were Reserved. This practice is implemented by Microsoft to maintain confidentiality and prevent users from understanding the structure to avoid modifications to these reserved members.
These reserved members are often presented as arrays of BYTE or PVOID data types.
Example -
typedef struct _PEB {
BYTE Reserved1[2];
BYTE BeingDebugged;
BYTE Reserved2[1];
PVOID Reserved3[2];
PPEB_LDR_DATA Ldr;
PRTL_USER_PROCESS_PARAMETERS ProcessParameters;
PVOID Reserved4[3];
PVOID AtlThunkSListPtr;
PVOID Reserved5;
ULONG Reserved6;
PVOID Reserved7;
ULONG Reserved8;
ULONG AtlThunkSListPtr32;
PVOID Reserved9[45];
BYTE Reserved10[96];
PPS_POST_PROCESS_INIT_ROUTINE PostProcessInitRoutine;
BYTE Reserved11[128];
PVOID Reserved12[1];
ULONG SessionId;
} PEB, *PPEB;
Microsoft’s official PEB documentation has many Reserved members.
One way is to determine what the PEB’s reserved members hold is through the !peb command in WinDBG.
// Microsoft's Documented One
typedef struct _PEB {
BYTE Reserved1[2];
BYTE BeingDebugged;
BYTE Reserved2[1];
PVOID Reserved3[2];
PPEB_LDR_DATA Ldr;
PRTL_USER_PROCESS_PARAMETERS ProcessParameters;
PVOID Reserved4[3];
PVOID AtlThunkSListPtr;
PVOID Reserved5;
ULONG Reserved6;
PVOID Reserved7;
ULONG Reserved8;
ULONG AtlThunkSListPtr32;
PVOID Reserved9[45];
BYTE Reserved10[96];
PPS_POST_PROCESS_INIT_ROUTINE PostProcessInitRoutine;
BYTE Reserved11[128];
PVOID Reserved12[1];
ULONG SessionId;
} PEB, *PPEB;
// Vergilius - Windows 11
//0x7d0 bytes (sizeof)
struct _PEB
{
UCHAR InheritedAddressSpace; //0x0
UCHAR ReadImageFileExecOptions; //0x1
UCHAR BeingDebugged; //0x2
union
{
UCHAR BitField; //0x3
struct
{
UCHAR ImageUsesLargePages:1; //0x3
UCHAR IsProtectedProcess:1; //0x3
UCHAR IsImageDynamicallyRelocated:1; //0x3
UCHAR SkipPatchingUser32Forwarders:1; //0x3
UCHAR IsPackagedProcess:1; //0x3
UCHAR IsAppContainer:1; //0x3
UCHAR IsProtectedProcessLight:1; //0x3
UCHAR IsLongPathAwareProcess:1; //0x3
};
};
UCHAR Padding0[4]; //0x4
VOID* Mutant; //0x8
VOID* ImageBaseAddress; //0x10
struct _PEB_LDR_DATA* Ldr; //0x18
struct _RTL_USER_PROCESS_PARAMETERS* ProcessParameters; //0x20
VOID* SubSystemData; //0x28
VOID* ProcessHeap; //0x30
struct _RTL_CRITICAL_SECTION* FastPebLock; //0x38
union _SLIST_HEADER* volatile AtlThunkSListPtr; //0x40
VOID* IFEOKey; //0x48
union
{
ULONG CrossProcessFlags; //0x50
struct
{
ULONG ProcessInJob:1; //0x50
ULONG ProcessInitializing:1; //0x50
ULONG ProcessUsingVEH:1; //0x50
ULONG ProcessUsingVCH:1; //0x50
ULONG ProcessUsingFTH:1; //0x50
ULONG ProcessPreviouslyThrottled:1; //0x50
ULONG ProcessCurrentlyThrottled:1; //0x50
ULONG ProcessImagesHotPatched:1; //0x50
ULONG ReservedBits0:24; //0x50
};
};
UCHAR Padding1[4]; //0x54
union
{
VOID* KernelCallbackTable; //0x58
VOID* UserSharedInfoPtr; //0x58
};
ULONG SystemReserved; //0x60
ULONG AtlThunkSListPtr32; //0x64
VOID* ApiSetMap; //0x68
ULONG TlsExpansionCounter; //0x70
UCHAR Padding2[4]; //0x74
struct _RTL_BITMAP* TlsBitmap; //0x78
ULONG TlsBitmapBits[2]; //0x80
VOID* ReadOnlySharedMemoryBase; //0x88
VOID* SharedData; //0x90
VOID** ReadOnlyStaticServerData; //0x98
VOID* AnsiCodePageData; //0xa0
VOID* OemCodePageData; //0xa8
VOID* UnicodeCaseTableData; //0xb0
ULONG NumberOfProcessors; //0xb8
ULONG NtGlobalFlag; //0xbc
union _LARGE_INTEGER CriticalSectionTimeout; //0xc0
ULONGLONG HeapSegmentReserve; //0xc8
ULONGLONG HeapSegmentCommit; //0xd0
ULONGLONG HeapDeCommitTotalFreeThreshold; //0xd8
ULONGLONG HeapDeCommitFreeBlockThreshold; //0xe0
ULONG NumberOfHeaps; //0xe8
ULONG MaximumNumberOfHeaps; //0xec
VOID** ProcessHeaps; //0xf0
VOID* GdiSharedHandleTable; //0xf8
VOID* ProcessStarterHelper; //0x100
ULONG GdiDCAttributeList; //0x108
UCHAR Padding3[4]; //0x10c
struct _RTL_CRITICAL_SECTION* LoaderLock; //0x110
ULONG OSMajorVersion; //0x118
ULONG OSMinorVersion; //0x11c
USHORT OSBuildNumber; //0x120
USHORT OSCSDVersion; //0x122
ULONG OSPlatformId; //0x124
ULONG ImageSubsystem; //0x128
ULONG ImageSubsystemMajorVersion; //0x12c
ULONG ImageSubsystemMinorVersion; //0x130
UCHAR Padding4[4]; //0x134
ULONGLONG ActiveProcessAffinityMask; //0x138
ULONG GdiHandleBuffer[60]; //0x140
VOID (*PostProcessInitRoutine)(); //0x230
struct _RTL_BITMAP* TlsExpansionBitmap; //0x238
ULONG TlsExpansionBitmapBits[32]; //0x240
ULONG SessionId; //0x2c0
UCHAR Padding5[4]; //0x2c4
union _ULARGE_INTEGER AppCompatFlags; //0x2c8
union _ULARGE_INTEGER AppCompatFlagsUser; //0x2d0
VOID* pShimData; //0x2d8
VOID* AppCompatInfo; //0x2e0
struct _UNICODE_STRING CSDVersion; //0x2e8
struct _ACTIVATION_CONTEXT_DATA* ActivationContextData; //0x2f8
struct _ASSEMBLY_STORAGE_MAP* ProcessAssemblyStorageMap; //0x300
struct _ACTIVATION_CONTEXT_DATA* SystemDefaultActivationContextData; //0x308
struct _ASSEMBLY_STORAGE_MAP* SystemAssemblyStorageMap; //0x310
ULONGLONG MinimumStackCommit; //0x318
VOID* SparePointers[2]; //0x320
VOID* PatchLoaderData; //0x330
struct _CHPEV2_PROCESS_INFO* ChpeV2ProcessInfo; //0x338
ULONG AppModelFeatureState; //0x340
ULONG SpareUlongs[2]; //0x344
USHORT ActiveCodePage; //0x34c
USHORT OemCodePage; //0x34e
USHORT UseCaseMapping; //0x350
USHORT UnusedNlsField; //0x352
VOID* WerRegistrationData; //0x358
VOID* WerShipAssertPtr; //0x360
VOID* EcCodeBitMap; //0x368
VOID* pImageHeaderHash; //0x370
union
{
ULONG TracingFlags; //0x378
struct
{
ULONG HeapTracingEnabled:1; //0x378
ULONG CritSecTracingEnabled:1; //0x378
ULONG LibLoaderTracingEnabled:1; //0x378
ULONG SpareTracingBits:29; //0x378
};
};
UCHAR Padding6[4]; //0x37c
ULONGLONG CsrServerReadOnlySharedMemoryBase; //0x380
ULONGLONG TppWorkerpListLock; //0x388
struct _LIST_ENTRY TppWorkerpList; //0x390
VOID* WaitOnAddressHashTable[128]; //0x3a0
VOID* TelemetryCoverageHeader; //0x7a0
ULONG CloudFileFlags; //0x7a8
ULONG CloudFileDiagFlags; //0x7ac
CHAR PlaceholderCompatibilityMode; //0x7b0
CHAR PlaceholderCompatibilityModeReserved[7]; //0x7b1
struct _LEAP_SECOND_DATA* LeapSecondData; //0x7b8
union
{
ULONG LeapSecondFlags; //0x7c0
struct
{
ULONG SixtySecondEnabled:1; //0x7c0
ULONG Reserved:31; //0x7c0
};
};
ULONG NtGlobalFlag2; //0x7c4
ULONGLONG ExtendedFeatureDisableMask; //0x7c8
};