Windows 10: Windows Defender Application Control Security Vulnerability

Brink · Jul 16, 2019

A security feature bypass vulnerability exists in Windows Defender Application Control (WDAC) which could allow an attacker to bypass WDAC enforcement. An attacker who successfully exploited this vulnerability could circumvent PowerShell Core Constrained Language Mode on the machine.

To exploit the vulnerability, an attacker would first have administrator access to the local machine where PowerShell is running in Constrained Language mode. By doing that an attacker could access resources in an unintended way.

The update addresses the vulnerability by correcting how PowerShell functions in Constrained Language Mode.

Exploitability Assessment

The following table provides an exploitability assessment for this vulnerability at the time of original publication.

Publicly Disclosed Exploited Latest Software Release Older Software Release Denial of Service No No Not Applicable Not Applicable Not Applicable
Security Updates

To determine the support life cycle for your software version or edition, see the Microsoft Support Lifecycle.

Product Platform Article Download Impact Severity Supersedence PowerShell Core 6.1 Release Notes Security Update Security Feature Bypass Important PowerShell Core 6.2 Release Notes Security Update Security Feature Bypass Important
Mitigations

Microsoft has not identified any mitigating factors for this vulnerability.

Workarounds

Microsoft has not identified any workarounds for this vulnerability.

Acknowledgements

See acknowledgements for more information.

Disclaimer

The information provided in the Microsoft Knowledge Base is provided "as is" without warranty of any kind. Microsoft disclaims all warranties, either express or implied, including the warranties of merchantability and fitness for a particular purpose. In no event shall Microsoft Corporation or its suppliers be liable for any damages whatsoever including direct, indirect, incidental, consequential, loss of business profits or special damages, even if Microsoft Corporation or its suppliers have been advised of the possibility of such damages. Some states do not allow the exclusion or limitation of liability for consequential or incidental damages so the foregoing limitation may not apply.

Revisions

Version Date Description 1.0 07/16/2019 Information published. 1.1 07/16/2019 Corrected vulnerability description. This is an informational change only.
Click to expand...

Source: https://portal.msrc.microsoft.com/en.../CVE-2019-1167

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Brink · Jul 16, 2019

Windows Defender Application Control enhancements in Windows 10 v1903

With the Windows 10 May 2019 Update we delivered several important features for Windows Defender Application Control (WDAC), which was originally introduced to Windows as part of a scenario called Device Guard. WDAC works in conjunction with features like Windows Defender Application Guard, which provides hardware-based isolation of Microsoft Edge for enterprise-defined untrusted sites, to strengthen the security posture of Windows 10 systems.

*Arrow How to Turn On or Off Windows Defender Application Guard for Microsoft Edge in Windows 10

*Arrow How to Enable or Disable Device Guard in Windows 10

Our focus for this release was responding to some longstanding feedback on manageability improvements. We’re excited to introduce the following new capabilities in Windows Defender Application Control:

File path rules, including optional runtime admin protection checks

Multiple policy file support with composability

Application Control CSP to provide a new, richer MDM policy management capability

COM object registration support in policy

Disabling script enforcement rule option

Application control is frequently identified as one of the most effective mitigations against modern security threats, because anything that’s not allowed by policy is blocked from running. Even striving towards a simple policy like mandating that only signed code is allowed to execute can be incredibly impactful: in a recent analysis of Windows Defender ATP data, we saw that 96% of malware encountered is unsigned. Systems like Windows 10 in S mode, which uses WDAC technology to enforce that all code must be signed by Windows and Microsoft Store code signing certificates, have no malware infection issues.

The new capabilities are designed to ease the journey for customers adopting application control in real-world environments with large numbers of applications, users, and devices.

File path rules, including optional runtime admin protection checks

For many customers looking to adopt application execution control while balancing IT overhead, rules based on file paths on managed client systems provide a useful model. The Windows 10 May 2019 Update introduces support for both allow and deny rules based on file path in Windows Defender Application Control.

File path rules had been one of the few features available in AppLocker, the older native application control technology, that were not available to WDAC; deployment tools and methodologies built on top of AppLocker like AaronLocker have relied on these rules as an important simplifying option for policy management. As we sought to close that gap, we wanted to preserve the stronger security posture available with WDAC that customers have come to expect. To this end, WDAC applies, by default, an option to check at runtime that apps and executables allowed based on file path rules must come from a file path that’s only writable by administrator or higher privileged accounts. This runtime check provides an additional safeguard for file path rules that are otherwise inherently weaker than other identifiers like hash or signer rules, which rely on cryptographically verifiable attributes.

This runtime capability can be controlled with the “Disabled:Runtime FilePath Rule Protection” rule option.

The following example shows how to easily create rules for anything allowed under “Program Files” and “Program Files (x86)”, and then merge them with the sample policy that allows all Windows signed code (available under C:\Windows\schemas\CodeIntegrity\ExamplePolicies). The resulting merged policy file allows all Windows signed code and applications installed under “Program Files” and “Program Files (x86)” with the runtime protection that checks that anything executing under those paths is coming from a location only writable by administrator or higher privileged accounts.

Multiple policy file support with composability

Limiting support to a single policy file means that a variety of app control scenarios from potentially different stakeholders or business groups need to be maintained in one place. This comes with an associated overhead: the coordination required to converge on the appropriate rules encapsulated in a single policy file.

With the Windows 10 May 2019 Update multiple policy files are supported for WDAC. To facilitate composing behavior from multiple policy files, we have introduced the concept of base and supplemental policies:

Base policies – For any execution to be allowed, the application must pass each base policy independently. Base policies are used together to further restrict what’s allowed. For example:
Let’s assume a system has two policies: Base Policy A and Base Policy B with their own sets of rules. For foo.exe to run, it must be allowed by the rules in Base Policy A and also the rules in Base Policy B. Windows Defender Application Control policies on prior Windows 10 systems will continue to work on the May 2019 Update and will be treated as base policies.

Supplemental policies – As the name suggests, supplemental policies complement base policies with additional rules to be considered as part of the base policies they correspond to. Supplemental policies are tied to a specific base policy with an ID; a base policy may have multiple supplemental policies. Supplemental policies expand what is allowed by any base policy, but deny rules specified in a supplemental policy will not be honored.

Application Control CSP

Customers have been able to deploy Windows Defender Application Control policies via MDM using the CodeIntegrity node of the AppLocker configuration service provider (CSP). The AppLocker CSP has a number of limitations, most notably the lack of awareness of rebootless policy deployment support.

The Windows 10 May 2019 Update now has a new Application Control CSP, which introduces much richer support for policy deployment over MDM and also provides support for:

Rebootless policy deployment (For policies that have the “Enabled:Update Policy No Reboot” option set, the new Application Control CSP will not schedule a reboot on client systems getting the policy)

Support for the new multiple policies

For device management software vendors, better error reporting

COM object registration support

Windows Defender Application Control enforces a built-in allow list of COM object registrations to reduce the risk introduced from certain powerful COM objects. Customers have reported that while this capability is desirable from a security perspective, there are specific cases in their environments where they’d like to allow the registration of additional COM objects required for their business.

With the Windows 10 May 2019 Update customers can now specify COM objects that need to be allowed in environments they’re managing with Windows Defender Application Control policies.

Disabled: Script Enforcement rule option support

The Windows 10 May 2019 Update with KB4497935 introduces proper support for the Disabled: Script Enforcement rule option.

Customers recognize the importance of having restrictions on script hosts but are often looking to break up their application control projects into smaller chunks to help with deployment feasibility. The “Disabled:Script Enforcement” rule option in the policy now turns off policy enforcement for MSIs, PowerShell scripts, and wsh-hosted scripts. This will allow IT departments to tackle EXE, DLL, and driver enforcement without needing to also simultaneously address script host control.

Try the new capabilities today

We invite everyone to try these new Windows Defender Application Control capabilities, alongside existing features like managed installer. For customers using Microsoft Defender ATP, consider using Advanced hunting to query the WDAC events centrally to understand and monitor the behavior of all these new policy controls on client machines in your environment. Learn about both new and existing functionalities with the Windows Defender Application Control deployment guide.

We’re also working on supplementing the documentation we have out now. Stay tuned for updates from our team for tools and guidance on GitHub that provide more practical examples and ready-to-use scripts.

Nazmus Sakib
Senior Program Manager, Windows Defender Application Control team
Click to expand...

Source: https://www.microsoft.com/security/b...y-2019-update/

Shafeeq_Khan · Jul 16, 2019

Use Windows Defender Application Control (WDAC) with the Microsoft Intelligent Security Graph

Hi,

Thank you for writing to Microsoft Community Forums.

In order to enable trust for executables based on classifications in the ISG, the
Enabled:Intelligent Security Graph authorization option must be specified in the WDAC policy. This can be done with the Set-RuleOption cmdlet. In addition, it is recommended from a security perspective to also enable the
Enabled:Invalidate EAs on Reboot option to invalidate the cached ISG results on reboot to force rechecking of applications against the ISG.

Since the ISG relies on identifying executables as being known good, there are cases where it may classify legitimate executables as unknown, leading to blocks that need to be resolved either with a rule in the WDAC policy, a catalog signed by a certificate
trusted in the WDAC policy or by deployment through a WDAC managed installer. Typically, this is due to an installer or application using a dynamic file as part of execution. These files do not tend to
build up known good reputation. Auto-updating applications have also been observed using this mechanism and may be flagged by the ISG.

Modern apps are not supported with the ISG heuristic and will need to be separately authorized in your WDAC policy. As modern apps are signed by the Microsoft Store and Microsoft Store for Business. It is straightforward to authorize modern apps with
signer rules in the WDAC policy.

Enabled:Intelligent Security Graph Authorization -> Use this option to automatically allow applications with "known good" reputation as defined by Microsoft’s Intelligent Security Graph (ISG).

Enabled:Invalidate EAs on Reboot -> When the Intelligent Security Graph option (14) is used, WDAC sets an extended file attribute that indicates that the file was authorized to run. This option will cause WDAC to periodically
re-validate the reputation for files that were authorized by the ISG.

For more information, you may refer the below articles.

Use
Windows Defender Application Control (WDAC) with the Microsoft Intelligent Security Graph.

Deploy Windows
Defender Application Control policy rules and file rules.

Use
signed policies to protect Windows Defender Application Control against tampering.

If you still have questions, then I suggest you to post your query in
IT Pro TechNet Forums, where we have support
professionals who are well equipped with the knowledge on Windows Defender Application Control (WDAC) with the Microsoft Intelligent Security Graph.

Please feel free to contact us back, in case you have any other questions/issues with Windows in future.

Yukikaze · Jul 16, 2019

WPA2 Vulnerability Found

A small update with regards to the Microsoft fix. The fix itself is sufficient to solve the issue on Windows, even if your WiFi device has no driver update, with one caveat:

Does this security update fully address these vulnerabilities on Microsoft Platforms, or do I need to perform any additional steps to be fully protected?
The provided security updates address the reported vulnerabilities; however, when affected Windows based systems enter a connected standby mode in low power situations, the vulnerable functionality may be offloaded to installed Wi-Fi hardware. To fully address potential vulnerabilities, you are also encouraged to contact your Wi-Fi hardware vendor to obtain updated device drivers. For a listing of affected vendors with links to their documentation, review the ICASI Multi-Vendor Vulnerability Disclosure statement here: http://www.icasi.org/wi-fi-protected-access-wpa-vulnerabilities

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