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Category: Security

The Prevalence of Persistent XSS

Published 2019-04-12 by Kevin Feasel

Adrian Colyer has a review of a security-minded paper:

Does your web application make use of local storage? If so, then like many developers you may well be making the assumption that when you read from local storage, it will only contain the data that you put there. As Steffens et al. show in this paper, that’s a dangerous assumption! The storage aspect of local storage makes possible a particularly nasty form of attack known as a persistent client-side cross-site scripting attack. Such an attack, once it has embedded itself in your browser one time (e.g. that one occasion you quickly had to jump on the coffee shop wifi), continues to work on all subsequent visits to the target site (e.g., once you’re back home on a trusted network).

In an analysis of the top 5000 Alexa domains, 21% of sites that make use of data originating from storage were found to contain vulnerabilities, of which at least 70% were directly exploitable using the models described in this paper.

Adrian’s been on a security paper kick the last few days, so be sure to check those out.

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Using Windows Authentication on Non-Windows Devices

Published 2019-04-05 by Kevin Feasel

Drew Furgiuele shows us how to connect to SQL Server using Windows Authentication if you’re not coming from a Windows device:

SQL Server supports different kinds of authentication mechanisms and protocols: the older NTLM protocol, and Kerberos. A lot of people cringe when you mention Kerberos because, well, Kerberos is hard. It’s arcane, it’s complex, and it’s hard to even describe unless you use it on the regular.

Simply put, it’s a ticketing and key system: you, a user, requests a ticket from a store, usually by authenticating to it via a username and password. If you succeed, you get a ticket that get stored within your local machine. Then, when you want to access a resource (like a SQL Server), the client re-ups with the store you got your initial ticket from (to make sure it’s still valid), and you get a “key” to access the resource. That key is then forwarded onto the resource, allowing you to access the thing you were trying to connect to. It’s way, way more complex than this, with lots of complicated terms and moving parts, so I’m doing a lot of hand-waving, but that’s the core of the system. If that kind of stuff excites you, go Google it, and I promise you’ll get more than you ever bargained for.

Kerberos is a scary beast to me, mostly because I don’t spend enough time working directly with it.

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Deploying Azure Databricks in a Custom VNET

Published 2019-03-29 by Kevin Feasel

Abhinav Garg and Anna Shrestinian explain how you can use VNET injection with Azure Databricks:

To make the above possible, we provide a Bring Your Own VNET (also called VNET Injection) feature, which allows customers to deploy the Azure Databricks clusters (data plane) in their own-managed VNETs. Such workspaces could be deployed using Azure Portal, or in an automated fashion using ARM Templates, which could be run using Azure CLI, Azure Powershell, Azure Python SDK, etc.

With this capability, the Databricks workspace NSG is also managed by the customer. We manage a set of inbound and outbound NSG rules using a Network Intent Policy, as those are required for secure, bidirectional communication with the control/management plane. 

This is a good article if the defaults won’t get past corporate security.

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Backing Up SSRS Encryption Keys

Published 2019-03-25 by Kevin Feasel

Jonathan Kehayias reminds us to back up those SQL Server Reporting Services encryption keys:

If you run SQL Server Reporting Services, part of your DR plan needs to include a backup of the encryption key for SSRS. This sadly is an all to often overlooked part of the solution, even though it is incredibly easy to do. If you don’t have a backup of the encryption key during a restore, the report server will never be able to decrypt the encrypted content (connection strings, passwords, etc) stored in the database, and your only recourse would be to delete the encrypted content and recreate it manually or through a redeployment of datasources.

Jonathan includes a couple of links to good resources. Your backups are only good if they include all of the keys and certificates you used. But keep those certificates stored someplace other than where the backups are stored.

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L-Diversity versus K-Anonymity

Published 2019-03-15 by Kevin Feasel

Duncan Greaves explains the concepts behind l-diversity:

There are problems with K-anonymous datasets, namely the homogeneous pattern attack, and the background knowledge attack, details of which are in my original post. A slightly different approach to anonymising public datasets comes in the form of ℓ -diversity, a way of introducing further entropy/diversity into a dataset.

A sensitive data record is made of the following microdata types: the ID; any Key Attributes; and the confidential outcome attribute(s). ℓ -diversity seeks to extend the equivalence classes that we created using K-anonymity by generalisation and masking of the quasi-identifiers (the QI groups) to the confidential attributes in the record as well. The ℓ -diversity principle demands that, in each QI-group, at most 1/ ℓ of its tuples can have an identical sensitive attribute value.

L-diversity is not perfect either, but Duncan gives a good explanation of the topic.

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Building a VPC with AWS

Published 2019-03-14 by Kevin Feasel

Priyaj Kumar takes us through the process of building a Virtual Private Cloud in AWS:

AWS provides a lot of services, these services are sufficient to run your architecture. The backbone for the security of this architecture is VPC (Virtual Private Cloud). VPC is basically a private cloud in the AWS environment that helps you to use all the services by AWS in your defined private space. You have control over the virtual network and you can also restrict the incoming traffic using security groups.

Overall, VPC helps you to secure your environment and give you a complete authority of incoming traffic. There are two types of VPCs, Default VPC that is by default created by Amazon and Non-Default VPC that is created by you to suffice your security needs.

Now that you have an idea of how VPC works, I will take you through the different services offered by Amazon VPC.

Read on to see how to set one up.

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Which Power BI Visuals Send Data Externally

Published 2019-03-01 by Kevin Feasel

Meagan Longoria does a bit of investigation into data privacy and Power BI visuals:

One thing that makes understanding data privacy in custom visuals easier is the designation of a certified custom visual. One of the requirements for certification is ” Does not access external services or resources, including but not limited to, no HTTP/S or WebSocket requests go out of Power BI to any services.”

You can find the list of currently certified custom visuals on this page. Custom visuals are also identified in the marketplace by a blue star with a check mark.

Read on for some good investigative analysis.

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Issues From Using gMSA Accounts with Docker

Published 2019-02-28 by Kevin Feasel

Michal Poreba shares some lessons from trying to set up Docker and SQL Server to use gMSA accounts:

While in the end I was able to make it work on Windows Server 2016, 1803, 2019 and 1809 I wasted some time trying to make it work with docker 17.06. Unsuccessfully. Docker 18.09.1 and 18.09.2 worked every time.
There are some reports of intermittent problems with specific OS updates breaking stuff, like the one here but I wasn’t able to reproduce it. I wonder if the updates changes something else that it causing problems, in other words is it the problem with the update itself or the update process?

Read on for several helpful tips, as well as dead ends to avoid.

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Group Managed Service Accounts

Published 2019-02-27 by Kevin Feasel

Jamie Wick explains Group Managed Service Accounts and uses Powershell to create them for use on a new SQL Server instance:

Service Accounts are a requirement for installing and running a SQL Server. For many years Microsoft has recommended that each SQL Server service be run as a separate low-rights Windows account. Where possible, the current recommendation is to use Managed Service Accounts (MSA) or Group Managed Service Accounts (gMSA
). Both account types are ones where the account password is managed by the Domain Controller. The primary difference being that MSA are used for standalone SQL instances, whereas clustered SQL instances require gMSA. In this post, we’re going to use PowerShell to create Group Managed Service Accounts, and then deploy them for use on multiple SQL servers that will be hosting an Availability Group.

Click through for more explanation as well as several scripts showing how to create and use them.

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