Python 3.6 audioop.adpcm2lin Buffer Over-Read

Credit: John Leitch
Risk: Medium
Local: Yes
Remote: No
CWE: CWE-119

Title: Python 2.7 and 3.4 to 3.6 audioop.adpcm2lin Buffer Over-read Credit: John Leitch ( Url1: Url2: Resolution: Fixed The Python 2.7, 3.4 - 3.6 audioop.adpcm2lin function suffers from a buffer over-read caused by unchecked access to stepsizeTable at line 1545 of Modules\audioop.c: } else if ( !PyArg_ParseTuple(state, "ii", &valpred, &index) ) return 0; step = stepsizeTable[index]; Because the index variable can be controlled via the third parameter of audioop.adpcm2lin, this behavior could potentially be exploited to disclose arbitrary memory, should an application expose the parameter to the attack surface. 0:000> r eax=01f13474 ebx=00000000 ecx=00000002 edx=01f13460 esi=01f13460 edi=00000001 eip=1e01c4f0 esp=0027fcdc ebp=7e86ecdd iopl=0 nv up ei pl nz na po nc cs=0023 ss=002b ds=002b es=002b fs=0053 gs=002b efl=00010202 python27!audioop_adpcm2lin+0xe0: 1e01c4f0 8b04adb0dd1f1e mov eax,dword ptr python27!stepsizeTable (1e1fddb0)[ebp*4] ss:002b:183b9124=???????? 0:000> k ChildEBP RetAddr 0027fd18 1e0aafd7 python27!audioop_adpcm2lin+0xe0 0027fd30 1e0edd10 python27!PyCFunction_Call+0x47 0027fd5c 1e0f017a python27!call_function+0x2b0 0027fdcc 1e0f1150 python27!PyEval_EvalFrameEx+0x239a 0027fe00 1e0f11b2 python27!PyEval_EvalCodeEx+0x690 0027fe2c 1e11707a python27!PyEval_EvalCode+0x22 0027fe44 1e1181c5 python27!run_mod+0x2a 0027fe64 1e118760 python27!PyRun_FileExFlags+0x75 0027fea4 1e1190d9 python27!PyRun_SimpleFileExFlags+0x190 0027fec0 1e038d35 python27!PyRun_AnyFileExFlags+0x59 0027ff3c 1d00116d python27!Py_Main+0x965 0027ff80 76477c04 python!__tmainCRTStartup+0x10f 0027ff94 7799ad1f KERNEL32!BaseThreadInitThunk+0x24 0027ffdc 7799acea ntdll!__RtlUserThreadStart+0x2f 0027ffec 00000000 ntdll!_RtlUserThreadStart+0x1b 0:000> To fix this issue, it is recommended that bounds checking be performed prior to accessing stepsizeTable.


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