FIX: Windows NT 4.0 w/ SP4 Causes Data Corruption in RPC Calls (216766)

SYMPTOMS

If you have a pointer to conformant structure as a field of a complex structure under Windows NT 4.0 with Service Pack 4 (SP4), the unmarshaling side gets uninitialized data. If such a data structure is an [in] parameter, the server manager routine sees the corruption. If it is an [out] parameter the corruption, the client sees the corruption.

The same problem appears if your RPC application is running on Windows 95 with DCOM95 1.2 update or Windows 98 with DCOM98 update as documented in the following article in the Microsoft Knowledge Base:

216889 FIX: DCOM95 1.2 or DCOM98 Causes Data Corruption in RPC Calls

Data Structure:

typedef struct tagConformantStruct 
{
   unsigned long        size;
   [size_is(size)] char data[];
} ConformantStruct;

typedef enum tagColor
{
   Red, Blue, Green
} Color;

typedef union tagMyUnion switch (Color type) u
{
   case Red :  long  longArm;
   case Blue:  short shortArm;
   case Green: char  charArm;
} MyUnion;

typedef struct tagComplexStruct
{
   unsigned long numUnions;
   ConformantStruct* pConfStruct; // PROBLEM! pointer to conformant struct.
   [size_is(numUnions)] MyUnion myUnions[]; // Makes the struct complex.
} ComplexStruct;

CAUSE

A defect in the rpcrt4.dll that is shipped with Windows Service Pack 4 (DCOM95 1.2) and DCOM98 prevents the conformant part of the conformant structure to be marshaled. The unmarshaling side expects the conformant part and unmarshals from a possibly uninitialized part of the RPC buffer. This causes data corruption.

RESOLUTION

Windows NT 4.0

To resolve this problem, obtain the latest service pack for Windows NT 4.0 or the individual software update. For information on obtaining the latest service pack, please go to:

http://www.microsoft.com/windows/servicepacks/ -or-
152734 how to obtain the latest windows nt 4.0 service pack

For information on obtaining the individual software update, contact Microsoft Product Support Services. For a complete list of Microsoft Product Support Services phone numbers and information on support costs, please go to the following address on the World Wide Web:

http://support.microsoft.com/directory/overview.asp

Windows NT Server 4.0, Terminal Server Edition

To resolve this problem, obtain the latest service pack for Windows NT Server 4.0, Terminal Server Edition. For additional information, click the following article number to view the article in the Microsoft Knowledge Base:

152734 How to Obtain the Latest Windows NT 4.0 Service Pack

STATUS

Microsoft has confirmed that this is a problem in Windows NT 4.0 Service Pack 4 and Windows NT Server 4.0, Terminal Server Edition Service Pack 4. This problem was first corrected in Windows NT version 4.0 Service Pack 5 and Windows NT Server 4.0, Terminal Server Edition Service Pack 5.