Core Security - CoreLabsSymantec Intel Handler Service Remote DoS
Title: Symantec Intel Handler Service Remote DoS
Advisory Id: CORE-2010-0728
Advisory URL: http://www.coresecurity.com/content/symantec-intel-handler-service-remote-dos
Date published: 2010-12-13
Date of last update: 2010-12-13
Vendors contacted: Symantec
Release mode: User release
The Intel Alert Handler service (
hndlrsvc.exe) fails to correctly process the 'CommandLine' field in the AMS request. A source address in a
MOV instruction is calculated from values present in the request, causing a remote denial-of-service.
The Intel Alert Management System is only present in versions of Symantec Endpoint Protection previous to 11.x. During the SEP 11.x engineering phase SEP was rewritten so that it no longer uses Intel AMS code. The installation of AMS is disabled by default for SEP versions that include it. The only workaround is to disable Intel AMS.
This vulnerability was discovered and researched by Nahuel Riva from Core Security Technologies. Publication was coordinated by Jorge Lucángeli Obes.
The request is handled in
prgxhndl.dll, called from
hndlsrvc.exe, more specifically from function
501A105D /. 55 PUSH EBP 501A105E |. 8BEC MOV EBP,ESP 501A1060 |. 81EC 60040000 SUB ESP,460 501A1066 |. 8D45 F4 LEA EAX,DWORD PTR SS:[EBP-C] 501A1069 |. 57 PUSH EDI 501A106A |. 50 PUSH EAX 501A106B |. 68 34301A50 PUSH prgxhndl.501A3034 ; ASCII "CommandLine" 501A1070 |. FF75 0C PUSH DWORD PTR SS:[EBP+C] 501A1073 |. 8BF9 MOV EDI,ECX 501A1075 |. FF75 08 PUSH DWORD PTR SS:[EBP+8] 501A1078 |. E8 33010000 CALL <JMP.&HNDLRSVC.#17_?[GetString@AMSHandler](<mailto:GetString@AMSHandler>)@@QAEHPAXKPADPAPAD@Z>
Inside that function,
GetStringAMSHandler() is called to parse the content of the 'CommandLine' field present in the request. In turn,
GetStringAMSHandler() forwards the request to function
AMSLIB.18 present in
AMSLIB.dll, and this function ends up calling the function that crashes,
AMSGetPastParamList(), also in
500733AE |. 8B45 E4 MOV EAX,DWORD PTR SS:[EBP-1C] 500733B1 |. 50 PUSH EAX ; /Arg1 500733B2 |. E8 54F3FFFF CALL AMSLIB.AMSGetPastParamList ; \AMSGetPastParamList
The crash occurs at address
50072786 |. 8B45 F0 |MOV EAX,DWORD PTR SS:[EBP-10] 50072789 |. 33C9 |XOR ECX,ECX 5007278B |. 8A08 |MOV CL,BYTE PTR DS:[EAX] 5007278D |. 85C9 |TEST ECX,ECX 5007278F |. 75 16 |JNZ SHORT AMSLIB.500727A7
When trying to read at the memory area pointed to by EAX, this value is invalid and the service crashes. This part of the code is parsing (inside a loop) the argument passed in the 'CommandLine' parameter. It seems that in many parts of the loop the pointer that is loaded from
[EBP-10] is calculated from a value present in the request.
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