CVE-2019-0731 : Detail

CVE-2019-0731

7.8
/
High
A01-Broken Access Control
69.84%V3
Local
2019-04-09
18h15 +00:00
2019-04-17
00h06 +00:00
CVE.org
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CVE Descriptions

An elevation of privilege vulnerability exists when Windows improperly handles calls to the LUAFV driver (luafv.sys), aka 'Windows Elevation of Privilege Vulnerability'. This CVE ID is unique from CVE-2019-0730, CVE-2019-0796, CVE-2019-0805, CVE-2019-0836, CVE-2019-0841.

CVE Informations

Related Weaknesses

CWE-ID Weakness Name Source
CWE-264 Category : Permissions, Privileges, and Access Controls
Weaknesses in this category are related to the management of permissions, privileges, and other security features that are used to perform access control.

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 : 46714

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

Windows: LUAFV Delayed Virtualization Cross Process Handle Duplication EoP Platform: Windows 10 1809 (not tested earlier) Class: Elevation of Privilege Security Boundary (per Windows Security Service Criteria): User boundary Summary: The LUAFV driver doesn’t take into account a virtualized handle being duplicated to a more privileged process resulting in EoP. Description: When a caller creates the virtualized file handle the process token is checked for VirtualizationEnabled. If the flag is set and the file create request meets all the criteria for delayed virtualization the driver collates all the necessary information such as the virtual store location for the resulting file if it needs to be copied and stores it in the file object’s context. When a caller performs an operation on the file which is considered a write action, such as writing or issuing any FsControl request then the method LuafvPreWrite is called which will call LuafvPerformDelayedVirtualization. This results in the store file being created and the contents of the original file copied into the new store file before assigning the new file to the original “fake” file object so that the user can continue to use the file. The vulnerability occurs during LuafvPerformDelayedVirtualization. The driver doesn’t take into account the possibility that the virtualized file handle has been duplicated to a new process, specifically one which runs at higher privileges. For example if a normal user application creates the virtualized file, but then gets a SYSTEM service to duplicate the handle to itself and call one of the mechanisms to trigger LuafvPerformDelayedVirtualization the file creation will run as the SYSTEM user not the original user, but the path to the file will be the original user’s virtual store. Examples of possible duplicate primitives would be RPC/COM services which duplicate the handle either explicitly through the system_handle RPC attribute or manually by querying for the caller’s PID and calling DuplicateHandle. Another would be a kernel driver which opens a handle in the current user’s context (or takes a handle parameter) but passes that handle to a system thread for a long running operation. In both these cases the file operation does have to occur without the privileged service impersonating the original caller. You can exploit this behavior in at least two ways. Firstly you could replace the virtual store directory with a mount point. When the virtualization process goes to create the final file it will follow the mount point and create the file in an arbitrary location. The contents of the file are completely controllable by the caller, but even if the privileged code overwrites part of the file the original opened handle can be used to get write access to the file afterwards. The second way would be to drop a hardlink to a file that the privileged service can write to in the virtual store, then when the file is opened by the service it becomes possible for the original caller to modify the file. Fixing wise I’d probably double check something in LuafvPerformDelayedVirtualization before continuing with the file copy. Perhaps something as simple as user SID + IL would be sufficient, or only for users in the same authentication session as that would even prevent its abuse in UAC cases. These operations can’t be done from any sandbox that I know of so it’s only a user privilege escalation. Note that the user which manipulates the duplicated handle doesn’t need to be an admin, as it’d be possible to modify files owned by that user so it might be possible to abuse this for cross-session or LOCAL SERVICE/NETWORK SERVICE attacks. Proof of Concept: I’ve provided a PoC as a C# project. It will create the file dummy.txt with arbitrary contents inside the windows folder. Note that this PoC is manual, I’ve not gone through and worked out a system service which will perform the necessary operations but I’m confident one will exist as handle duplication is a fairly common technique and you don’t even need to write to the file just perform one of the known actions. 1) Compile the C# project. It’ll need to pull NtApiDotNet from NuGet to build. 2) As a normal user run the PoC. If there are no errors you should see the line: “Re-run the PoC as an admin with arguments - X Y”. 3) Run as the PoC again as an admin, passing X and Y as arguments from step 2. This admin can be SYSTEM, it doesn’t matter what session or user it runs as. Expected Result: The virtualization operation fails. Observed Result: The virtualization operation succeeds and the file c:\windows\dummy.txt is created with arbitrary contents. Proof of Concept: https://gitlab.com/exploit-database/exploitdb-bin-sploits/-/raw/main/bin-sploits/46714.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/46714/
Tags : exploit, x_refsource_EXPLOIT-DB