A detailed introduction to MsMpEng can be found in issue #1252 , so I will skip the background story here.
Through fuzzing, we have discovered a number of ways to crash the service (and specifically code in the mpengine.dll module), by feeding it with malformed input testcases to scan. A summary of our findings is shown in the table below:
+==============+===================================+==========================+=============+====================================================+=============================================+
| Name | Type | Requirements | Access Type | Observed symbol | Comments |
+==============+===================================+==========================+=============+====================================================+=============================================+
| corruption_1 | Heap buffer overflow | PageHeap for MpMsEng.exe | - | free() called by NET_thread_ctx_t__FreeState_void_ | One-byte overflow. |
+--------------+-----------------------------------+--------------------------+-------------+----------------------------------------------------+---------------------------------------------+
| corruption_2 | Heap corruption | PageHeap for MpMsEng.exe | - | free() called by CRsaPublicKey__Decrypt_uchar | May crash in other ways, e.g. invalid read. |
+--------------+-----------------------------------+--------------------------+-------------+----------------------------------------------------+---------------------------------------------+
| corruption_3 | Unspecified memory corruption (?) | - | - | netvm_parse_routine_netinvoke_handle_t | Different crashes with/out PageHeap. |
+--------------+-----------------------------------+--------------------------+-------------+----------------------------------------------------+---------------------------------------------+
| null_1 | NULL Pointer Dereference | - | READ | nUFSP_pdf__handleXFA_PDF_Value | |
+--------------+-----------------------------------+--------------------------+-------------+----------------------------------------------------+---------------------------------------------+
| null_2 | NULL Pointer Dereference | - | READ | nUFSP_pdf__expandObjectStreams_void | |
+--------------+-----------------------------------+--------------------------+-------------+----------------------------------------------------+---------------------------------------------+
| null_3 | NULL Pointer Dereference | - | READ | NET_context_unsigned | |
+--------------+-----------------------------------+--------------------------+-------------+----------------------------------------------------+---------------------------------------------+
| null_4 | NULL Pointer Dereference | - | READ | nUFSP_pdf__expandObjectStreams_void_ | Similar to null_2, may be the same bug. |
+--------------+-----------------------------------+--------------------------+-------------+----------------------------------------------------+---------------------------------------------+
| div_by_zero | Division by zero | - | - | x86_code_cost__get_cost_int | |
+--------------+-----------------------------------+--------------------------+-------------+----------------------------------------------------+---------------------------------------------+
| recursion | Deep/infinite recursion | - | - | __EH_prolog3_catch_GS | |
+--------------+-----------------------------------+--------------------------+-------------+----------------------------------------------------+---------------------------------------------+
The "corruption_1-3" issues are the most important ones, as they represent memory corruption problems and could potentially lead to execution of arbitrary code. On the other hand, "null_1-4", "div_by_zero" and "recursion" are low severity bugs that can only be used to bring the service process down. We have verified that all listed crashes occur on Windows 7 as soon as an offending sample is saved to disk and discovered by MsMpEng. For "corruption_1-2", the PageHeap mechanism must be enabled for the MsMpEng.exe program in order to reliably observe the unhandled exception.
Attached is a ZIP archive (password: "mpengbugs") with up to 3 testcases for each of the 9 unique crashes.
This bug is subject to a 90 day disclosure deadline. After 90 days elapse or a patch has been made broadly available, the bug report will become visible to the public.
