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Microsoft Jet DB engine vulnerabilities
Level: low-med-[HIGH]-crit ID: HEXVIEW200503311 URL: http://www.hexview.com/docs/20050331-1.txt
Microsoft Jet database is a lightweight database widely used by MS Office applications. msjet40.dll is the main component of the Microsoft Jet database engine which evaluates and carries out requests for data. The library handles reading and writing of the data for Microsoft Access databases. HexView noticed multiple occurrences where file data was not validated or improperly validated leading to system crashes, null pointer memory access conditions, and arbitrary code execution. This advisory is focused on just one vulnerability that we confirmed to be exploitable.
All tests were performed using the latest avaliable msjet40.dll library (version 4.00.8618.0). We did not test earlier versions, but it should be assumed that all earlier releases of the library are also vulnerable. Please note that MS JetDB OLE Provider (msjetoledb40.dll) is not affected by this problem. Only software products that utilize msjet40.dll are affected, including Microsoft Access.
Sufficient data validation is not performed when msjet40.dll parses the database file. As a result, it is possible to modify database file to cause a code of attacker's choice to be launched when MS Jet database is opened.
Below is a fragment of an empty *.mdb file. Note the sequence of 0x77 characters on line #3. When msjet40.dll parses this part of the file, it triggers an exception.
000023B0: 00 00 04 00-49 00 64 00-18 00 50 00-61 00 72 00 ....I.d...P.a.r. 000023C0: 65 00 6E 00-74 00 49 00-64 00 4E 00-61 00 6D 00 e.n.t.I.d.N.a.m. 000023D0: 65 00 77 77-77 77 00 00-05 06 00 00-08 00 02 06 e.wwww.......... 000023E0: 00 00 03 06-00 00 0D 00-08 06 00 00-09 06 00 00 ................ 000023F0: 10 00 0E 06-00 00 0F 06-00 00 0F 00-0C 06 00 00 ................
Below is a code fragment from msjet40.dll that is responsible for the crash. Atacker directly controls the value of AX. The value goes through a signed expansion that is used to access 32-bit pointer to the variable that stores the address of a call table.
movsx eax, ax mov ecx, [edi+eax*4+0B0h] mov edx, [ecx] call dword ptr [edx+10h]
The accessible memory range contains portions of original file, which makes possible to load instruction pointer with the value pointing to malicious code embedded in the document. The issue is trivial to exploit and the exploit is very portable as the attacker does not need to know absolute code addresses.
Microsoft was notified on March 30, 2005. Message acknowledged by an automated reply. No human response received.
HexView contributes to online security-related lists for almost a decade. The scope of our expertize spreads over Windows, Linux, Sun, MacOS platforms, network applications, and embedded devices. We also offer a variety of consulting services. For more information visit http://www.hexview.com
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