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Windows 10 security: Microsoft dismissed RDP flaw until it saw Hyper-V was affected



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Microsoft recently reversed a decision not to patch a flaw in its Remote Desktop Protocol (RDP) client after realizing the same flaw could be used to target its Hyper-V virtualization software in Windows 10 and Azure.   

Last October, Check Point researcher Eyal Itkin informed Microsoft of a flaw in its RDP client but was told his finding “is valid but does not meet our bar for servicing”, so it didn’t warrant a patch. 

However, Microsoft recently reversed its decision and released a patch for the remote code execution bug CVE-2019-0887 in July, which corrects “how Remote Desktop Services handles clipboard redirection”.    

The patch came after Itkin discovered an attacker could use the flaw in Microsoft’s RDP client for a sandbox escape or a “guest-to-host” virtual machine (VM) escape in Microsoft’s Hyper-V Manager. 

Microsoft security software engineer Dana Baril and Itkin detail the connection between the RDP client and Hyper-V in an aptly titled presentation at Black Hat on Wednesday, called ‘He Said, She Said – Poisoned RDP Offense and Defense’. The presentation covers a design flaw Hyper-V inherited from the RDP client. Check Point has also posted a blog explaining the connection. 

The connection is found in Microsoft’s use of RDP in Hyper-V ‘Enhanced Sessions’, which is on by default, and is designed to improve the experience when viewing virtual machines. Enhanced Sessions enables extra capabilities including sharing clipboard data between a guest and the host. 

Itkin’s earlier research probed multiple RDP clients to find out if an RDP server can gain control over a computer it’s connected to via the RDP client. Normally, an RDP client can gain access to a remote server and, by using its clipboard-sharing feature, enable users to copy and paste files to another computer. 

But Itkin found a path-traversal vulnerability in Microsoft’s RDP that allowed a malicious RDP server to send arbitrary files to a client and take it over through the clipboard-sharing feature. 

Leading up to Microsoft’s July patch, he found the RDP flaw worked in precisely the same way in the Hyper-V GUI.

“It turns out that RDP is used behind the scenes as the control plane for Hyper-V,” Itkin explains. “Instead of reimplementing screen-sharing, remote keyboard and synchronized clipboard features, Microsoft decided that all these features are already implemented as part of RDP, so why not use it in this case as well?”  

As the pair detail in a whitepaper, Microsoft designed clipboards to be used locally, and so that data should only be transferred to or from it in response to a user command. However, the assumptions this model makes about trust breaks down in an environment where machines share features. 

“Our research revealed this important design lesson, that when a feature was developed under certain circumstances, when the environment changes, features must be reconsidered,” the pair write. 

Microsoft has also detailed some of the cloud-based methods it developed for the Microsoft Defender Advanced Threat Protection service for detecting when an attacker exploits this vulnerability.   

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The Five Pillars of (Azure) Cloud-based Application Security



This 1-hour webinar from GigaOm brings together experts in Azure cloud application migration and security, featuring GigaOm analyst Jon Collins and special guests from Fortinet, Director of Product Marketing for Public Cloud, Daniel Schrader, and Global Director of Public Cloud Architecture and Engineering, Aidan Walden.

These interesting times have accelerated the drive towards digital transformation, application rationalization, and migration to cloud-based architectures. Enterprise organizations are looking to increase efficiency, but without impacting performance or increasing risk, either from infrastructure resilience or end-user behaviors.

Success requires a combination of best practice and appropriate use of technology, depending on where the organization is on its cloud journey. Elements such as zero-trust access and security-driven networking need to be deployed in parallel with security-first operations, breach prevention and response.

If you are looking to migrate applications to the cloud and want to be sure your approach maximizes delivery whilst minimizing risk, this webinar is for you.

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Data Management and Secure Data Storage for the Enterprise



This free 1-hour webinar from GigaOm Research brings together experts in data management and security, featuring GigaOm Analyst Enrico Signoretti and special guest from RackTop Systems, Jonathan Halstuch. The discussion will focus on data storage and how to protect data against cyberattacks.

Most of the recent news coverage and analysis of cyberattacks focus on hackers getting access and control of critical systems. Yet rarely is it mentioned that the most valuable asset for the organizations under attack is the data contained in these systems.

In this webinar, you will learn about the risks and costs of a poor data security management approach, and how to improve your data storage to prevent and mitigate the consequences of a compromised infrastructure.

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CISO Podcast: Talking Anti-Phishing Solutions



Simon Gibson earlier this year published the report, “GigaOm Radar for Phishing Prevention and Detection,” which assessed more than a dozen security solutions focused on detecting and mitigating email-borne threats and vulnerabilities. As Gibson noted in his report, email remains a prime vector for attack, reflecting the strategic role it plays in corporate communications.

Earlier this week, Gibson’s report was a featured topic of discussions on David Spark’s popular CISO Security Vendor Relationship Podcast. In it, Spark interviewed a pair of chief information security officers—Mike Johnson, CISO for SalesForce, and James Dolph, CISO for Guidewire Software—to get their take on the role of anti-phishing solutions.

“I want to first give GigaOm some credit here for really pointing out the need to decide what to do with detections,” Johnson said when asked for his thoughts about selecting an anti-phishing tool. “I think a lot of companies charge into a solution for anti-phishing without thinking about what they are going to do when the thing triggers.”

As Johnson noted, the needs and vulnerabilities of a large organization aligned on Microsoft 365 are very different from those of a smaller outfit working with GSuite. A malicious Excel macro-laden file, for example, poses a credible threat to a Microsoft shop and therefore argues for a detonation solution to detect and neutralize malicious payloads before they can spread and morph. On the other hand, a smaller company is more exposed to business email compromise (BEC) attacks, since spending authority is often spread among many employees in these businesses.

Gibson’s radar report describes both in-line and out-of-band solutions, but Johnson said cloud-aligned infrastructures argue against traditional in-line schemes.

“If you put an in-line solution in front of [Microsoft] 365 or in front of GSuite, you are likely decreasing your reliability, because you’ve now introduced this single point of failure. Google and Microsoft have this massive amount of reliability that is built in,” Johnson said.

So how should IT decision makers go about selecting an anti-phishing solution? Dolph answered that question with a series of questions of his own:

“Does it nail the basics? Does it fit with the technologies we have in place? And then secondarily, is it reliable, is it tunable, is it manageable?” he asked. “Because it can add a lot overhead, especially if you have a small team if these tools are really disruptive to the email flow.”

Dolph concluded by noting that it’s important for solutions to provide insight that can help organizations target their protections, as well as support both training and awareness around threats. Finally, he urged organizations to consider how they can measure the effectiveness of solutions.

“I may look at other solutions in the future and how do I compare those solutions to the benchmark of what we have in place?”

Listen to the Podcast: CISO Podcast

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