CVE-2019-0732 : Detail

CVE-2019-0732

7.8
/
High
Authorization problems
A01-Broken Access Control
72.07%V3
Local
2019-04-09
18h15 +00:00
2019-04-17
00h06 +00:00
CVE.org
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CVE Descriptions

A security feature bypass vulnerability exists in Windows which could allow an attacker to bypass Device Guard when Windows improperly handles calls to the LUAFV driver (luafv.sys), aka 'Windows Security Feature Bypass Vulnerability'.

CVE Informations

Related Weaknesses

CWE-ID Weakness Name Source
CWE-863 Incorrect Authorization
The product performs an authorization check when an actor attempts to access a resource or perform an action, but it does not correctly perform the check.

Metrics

Metrics Score Severity CVSS Vector Source
V3.0 7.8 HIGH CVSS:3.0/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

Base: Exploitabilty Metrics

The 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.

Local

A vulnerability exploitable with Local access means that the vulnerable component is not bound to the network stack, and the attacker's path is via read/write/execute capabilities. In some cases, the attacker may be logged in locally in order to exploit the vulnerability, otherwise, she may rely on User Interaction to execute a malicious file.

Attack Complexity

This metric describes the conditions beyond the attacker's control that must exist in order to exploit the vulnerability.

Low

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.

Low

The attacker is authorized with (i.e. requires) privileges that provide basic user capabilities that could normally affect only settings and files owned by a user. Alternatively, an attacker with Low privileges may have the ability to cause an impact only to non-sensitive resources.

User Interaction

This metric captures the requirement for a user, other than the attacker, to participate in the successful compromise of the vulnerable component.

None

The vulnerable system can be exploited without interaction from any user.

Base: Scope Metrics

An 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.

Unchanged

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 Metrics

The 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.

High

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.

High

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.

High

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 Metrics

The 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 4.6 AV:L/AC:L/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.
EPSS First.org

Exploit information

Exploit Database EDB-ID : 46716

Publication date : 2019-04-15 22h00 +00:00
Author : Google Security Research
EDB Verified : Yes

Windows: LUAFV NtSetCachedSigningLevel Device Guard Bypass Platform: Windows 10 1809 (not tested earlier). Note I’ve not tested this on Windows 10 SMode. Class: Security Feature Bypass Summary: The NtSetCachedSigningLevel system call can be tricked by the operation of LUAFV to apply a cached signature to an arbitrary file leading to a bypass of code signing enforcement under UMCI with Device Guard. Description: As I’ve hit this API multiple times by now I’m not going to explain its operation. The novel aspect of this issue is that you can get the LUAFV driver to win the signing race between reading the file to determine the hash to sign and the file the kernel EA is assigned to. The exploit is as follows: 1) Create a file with the contents of a valid Microsoft signed file, such as notepad.exe in a virtualized location. 2) Get LUAFV to virtualize that file by requesting DELETE access. DELETE is not considered a write access right for the purposes of any checks in the signing process. 3) Copy the unsigned executable to the virtual store with the target virtualized name. 4) Call NtSetCachedSigningLevel on the virtualized file specifying flag 4. This sequence results in the signing code reading the virtualized file, which contains the contents of notepad.exe and generating the signature based on that data. However when it goes to write the kernel EA the LUAFV driver considers that a write operation and virtualizes the file underneath. As we’ve created an arbitrary file in the virtual store the driver binds the file object to the unsigned file before writing out the kernel EA. This results in the EA going to the unsigned file rather than the original signed file. As you can’t virtualize files with executable extensions you must ensure the signed file has an allowed extension, however once you’ve signed the file you can rename it to something more appropriate. Note that I have checked that Windows 10 Pro SMode does load the LUAFV driver, however I’ve not checked that this bypass will work on it (but no reason to believe it doesn’t). Proof of Concept: I’ve provided a PoC as a C# project. It will sign an arbitrary DLL file the map it into memory with the Microsoft only signature mitigation enabled. 1) Compile the C# project. It’ll need to pull NtApiDotNet from NuGet to build. 2) As a normal user run the PoC passing the path to an unsigned DLL which will do something noticeable in DllMain (such as popping a message box). Expected Result: The cached signature operation fails. Observed Result: The an arbitrary file is cached signed and can be loaded with an elevated process signature level. Proof of Concept: https://gitlab.com/exploit-database/exploitdb-bin-sploits/-/raw/main/bin-sploits/46716.zip

Products Mentioned

Configuraton 0

Microsoft>>Windows_10 >> Version -

Microsoft>>Windows_10 >> Version 1607

Microsoft>>Windows_10 >> Version 1703

Microsoft>>Windows_10 >> Version 1709

Microsoft>>Windows_10 >> Version 1803

Microsoft>>Windows_10 >> Version 1809

Microsoft>>Windows_7 >> Version -

Microsoft>>Windows_8.1 >> Version -

Microsoft>>Windows_rt_8.1 >> Version -

Microsoft>>Windows_server_2008 >> Version -

Microsoft>>Windows_server_2008 >> Version r2

Microsoft>>Windows_server_2008 >> Version r2

Microsoft>>Windows_server_2012 >> Version -

Microsoft>>Windows_server_2012 >> Version r2

Microsoft>>Windows_server_2016 >> Version -

Microsoft>>Windows_server_2016 >> Version 1709

Microsoft>>Windows_server_2016 >> Version 1803

Microsoft>>Windows_server_2019 >> Version -

References

https://www.exploit-db.com/exploits/46716/
Tags : exploit, x_refsource_EXPLOIT-DB