CVE-2019-0796 : Detail

CVE-2019-0796

5.5
/
Medium
A01-Broken Access Control
41.96%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-2019-0731, 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 5.5 MEDIUM CVSS:3.0/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:H/A:N

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.

None

There is no loss of confidentiality within the impacted component.

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.

None

There is no impact to availability within the impacted component.

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 2.1 AV:L/AC:L/Au:N/C:N/I:P/A:N [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 : 46715

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

Windows: LUAFV LuafvCopyShortName Arbitrary Short Name 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 bypasses security checks to copy short names during file virtualization which can be tricked into writing an arbitrary short name leading to EoP. Description: When creating a virtualized file in LuafvCopyFile one of the things that the driver copies across is the short name of the original file by calling LuafvCopyShortName. This uses the FileShortNameInformation information class to set the short name, however the problem with using this is it normally requires SeRestorePrivilege to be enabled, which a non-administrator won’t have access to. Therefore to bypass the privilege check the virtualized file is reopened without security checks, which results in the check being ignored. The code looks roughly like the following: NSTATUS LuafvCopyShortName(PFLT_INSTANCE Instance, PFILE_OBJECT ReadObject, HANDLE WriteHandle) { HANDLE FileHandle; PFILE_OBJECT WriteObject; NTSTATUS = FltCreateFileEx2( LuafvDriverData, Instance, &FileHandle, &WriteObject, FILE_WRITE_ATTRIBUTES, ..., IO_NO_PARAMETER_CHECKING); FILE_NAME_INFORMATION Name = {}; if (NT_SUCCESS(status)) { if (NT_SUCCESS(FltQueryInformationFile(Instance, ReadHandle, &Name, sizeof(Name), FileAlternateNameInformation))) { status = FltSetInformationFile(Instance, WriteObject, &Name, IoStatusBlock.Information, FileShortNameInformation); } } return status; } We can see in the code the writable file is re-opened with new access and without specifying IO_FORCE_ACCESS_CHECK. As FILE_OPEN_FOR_BACKUP_INTENT is specified then NTFS will mark this file as having restore privilege, even though the caller doesn’t, as the previous mode will be KernelMode. The original file is then queried for its alternate name (which is really its short name) and the short name is set through the FileShortNameInformation which will now succeed due to the way the file handle was opened. Of course the question is how would you get this code to write an arbitrary short name? Although it’s not obvious if the name of the file is already a short name (as in a 8.3 DOS compatible name) then FileAlternateNameInformation doesn’t fail but returns the normal file name back to the caller. Therefore we can exploit this as follows: 1) Create a file with the arbitrary short name inside a directory which is virtualized, ProgramData is ideal for this as we can create arbitrary files. Make the file writeable only to administrators. 2) Open the file for virtualization, but don’t do anything to cause delayed virtualization to occur. 3) Use some symbolic tricks in the VirtualStore directory to cause the creation of that file to be redirected to a long name which would normally have an auto-generated short name. 4) Force the delayed virtualization to occur, the file with the long name will be created, however the short name will be read from the source file which has an arbitrary name. The short name is written bypassing security checks. There’s probably other ways of doing this without symbolic link tricks, for example there’s a race between the time the file is opened and when the short name is queries. As the file is opened with FILE_SHARE_DELETE it should be possible to rename the source file between the initial open but before reading the short name. What you could do with this ability is another matter. You could possibly trick some parsing operation which is relying on short names. Or you could create a directory which had two “normal” names rather than one auto generated one which could trick certain things. At any rate the EoP is the fact we can do this without needing SeRestorePrivilege. I’m not going to speculate on how to fix this, as said while you might be able to block mount point traversal (seems unlikely as the user’s profile could be on a remote share or another drive) there’s probably other ways around this. Proof of Concept: I’ve provided a PoC as a C# project. It will create an arbitrary file with an arbitrary short file name. 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 name of the target file to create (with a long file name) and the arbitrary short file name. Expected Result: The virtualization operation fails. Observed Result: The virtualization operation succeeds and the file has an arbitrary short name. Proof of Concept: https://gitlab.com/exploit-database/exploitdb-bin-sploits/-/raw/main/bin-sploits/46715.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/46715/
Tags : exploit, x_refsource_EXPLOIT-DB