Category Archives: tutorial

How To Build a SANS GIAC Index

Over the years, my most popular article has been about how to successfully pass SANS GIAC exams.  Most people focus on my second recommendation on building an index for the course material.  Unfortunately, the index guide I linked to is no longer available.  Since I’ve received a number of requests for the Word doc, I’ve decided to write my own version of how to do this.  Enjoy!

  1. Create a spreadsheet with tabs labeled for each book in the course.  For example, “503.1”, “503.2 + 503.3”, etc.
  2. Label the first four columns with: “Page”, “Keyword 1”, “Keyword 2”, and “Keyword 3”.
  3. Read through each course book and summarize each page into three keywords or phrases (e.g. “tcpdump output overview”, “nibble definition”, etc) and note these in your spreadsheet.  Skip this for any pages with no notable information.
  4. For each tab in the spreadsheet, insert a new column before column A and title it “Book”.  For each existing row of pages, populate the book number.
  5. Copy columns A (“Book”) and B (“Page”) and insert both of them before the columns for “Keyword 2” and “Keyword 3”.
  6. Cut the “Book”, “Page”, and “Keyword 3” block and paste them below their respective columns in A, B, and C.  Repeat this for the “Book”, “Page”, and “Keyword 2” block and place these under the “Keyword 3” block you just pasted.
  7. Repeat steps 4 – 6 for each tab in your spreadsheet and remember to save your work. 🙂
  8. Create a new tab in the spreadsheet titled, “Complete”.  This will contain all the data from the previous tabs.
  9. Copy and paste columns A, B, and C from each of the previous tabs into columns A, B, and C of the “Complete” tab.  Paste each new tab’s data below the previous.
  10. In the “Complete” tab, move column C (“Keyword 1”) before column A (“Book”).
  11. Sort the new column A (“Keyword”) alphabetically and perform any edits and formatting cleanup (e.g. remove rows with column headers due to pasting and any blank rows).  Congratulations, you have an index!

Hope this helps and best of luck on the exam!  You’ll do great. 🙂

One final note.  Please don’t ask for the indexes I created, as I will not be sharing them.  The whole point in building your own index is so you’ll learn and retain the material.  Asking for mine or taking someone else’s is a shortcut that will likely lead to your own disappointment come exam time. 😛

How to determine your Ring Doorbell Pro firmware version

I have a love/hate relationship with my Ring Doorbell.  When I purchased it in 2016 it worked great for a year with minimal issues.  As it became more popular, I noticed the quality dropped with video freezes, black videos, and missed motion events.  This led me to the Ring Doorbell subreddit where I found a community of users who were also experiencing the same issues.  This made me feel a bit better (misery loves company, right?) but still disappointed that this $250 doorbell no longer lived up to its promise.

A number of the users who shared their negative feedback traced some of the poor service to firmware changes.  It soon became commonplace to post your issues along with the firmware version your device was currently running.  Pretty basic troubleshooting practice.  So it was much to everyone’s dismay when in late 2017, Ring decided to change how they displayed firmware versions.  In short, if your device is on the latest version the mobile app would only display, “Up to Date” as opposed to an actual firmware version number.  But without an actual firmware version number to compare with others, for all you know your device may actually be on an older version but hasn’t properly updated itself such that it merely *thinks* it is up to date.  Presumably, if it was actually out of date, it will display a version number, but this is useless as you cannot manually force an upgrade.  And again, you can’t compare with others to know which version you should actually be on.  This also makes it difficult to track changes that Ring is making and correlate them to your device’s performance improvements or degradations.  As you might imagine, there was a lively Reddit discussion on this.

Being in the information security field, I know that software version numbers are critical to confirming that my application is fully patched against any identified security vulnerabilities.  Naturally, I was disappointed by this change and soon looked for ways to determine the version number using, what else?  My Palo Alto firewall.

I knew my Ring Doorbell had to communicate with Ring’s servers in some way to check if it was running the latest firmware version.  I figured an easy way for Ring to do this is via user agent strings.  So I first checked the Monitor tab to see if the user agent of the device appeared in the URL Filtering view.  Sadly, the user agent field was blank suggesting that it wasn’t normal http traffic that this information was in.  Still feeling confident that the user agent must be somewhere, I decided to run a packet capture through the Palo Alto via Monitor -> Packet Capture.

  1. Navigate to Configure Filtering -> Manage Filters.
  2. Click Add and configure the Source with the IP address of your Ring Doorbell.  I have mine statically assigned via my DHCP server but this should be fairly easy for you to determine either in your wireless router or your Palo Alto firewall.  Click OK when done.

3. Back in the Configure Filtering menu turn Filtering to ON.

4. In Configure Capturing click Add and select firewall for Stage and give your packet capture a file name. In this example I’ve used ringdoorbell.  Click OK and your view should look like the one below.

5. Once you’re ready, in the same view set Packet Capture to ON.  You’ll receive a warning about packet captures degrading system performance and to remember to disable the feature once you’re done.  Click OK to proceed.

6. Now we need to generate some traffic through the doorbell to hopefully find the user agent string in the packet captures.  Start a Live View session through your Ring mobile app and let it run for at least 30 seconds.  Once completed, set Packet Capture back to OFF.

7. Click the Refresh button in the top right corner or reload the page to find your newly created packet capture file in the Captured Files view.  Click on it to download the file to your computer.

8. You’ve got a few options to view this file.  Since I’m on a MacBook Pro, I’ll walk through how to use tcpdump to quickly find the user agent.  You could also use Wireshark to accomplish this.

Locate the file on your system and use the following tcpdump command: tcpdump -nn -r ringdoorbell.pcap -A | grep -i agent

tcpdump -nn -r ringdoorbell.pcap -A | grep -i agent
reading from file ringdoorbell.pcap, link-type EN10MB (Ethernet)
User-Agent: Device/lpdv2/1.13.00069
User-Agent: Device/lpdv2/1.13.00069
User-Agent: Device/lpdv2/1.13.00069
User-Agent: Device/lpdv2/1.13.00069

Voila!  You can see that my user agent shows that my Ring is on firmware version 1.13.00069.  From here, I could look for ways to automate this or periodically run this check manually and compare with previous captures to see if I can correlate Ring issues with changing firmware numbers.  Another way to possibly do this is to use my favorite security tool Bro to extract this automatically in real time.

I hope that Ring strongly reconsiders this change and reverts back to displaying the full firmware version number.  But in the meantime, I (and now you!) have a way to accurately determine this value.

Palo Alto Firewall: macOS Updates NSURLErrorDomain error -1012

About a month ago, I enabled decryption on my Palo Alto firewall and limited it only to traffic to and from my MacBook Pro.  It’s worked well and provided great visibility into the vast amounts of encrypted traffic that we see nowadays.

So what’s this have to do with macOS?  Apple periodically releases updates and I had read that one was just released.  I checked my laptop and saw that I had a few updates to install for the iWork suite and Xcode.  Notably missing were notifications for the core macOS system updates.  I clicked on the “Updates” button again in the Mac App Store and received the following message.:

“Oh, the operation couldn’t be completed because of the NSURLErrorDomain error -1012?  Great, real helpful.”  I tried closing an reopening the App Store with no luck.  I thought maybe my laptop just wasn’t happy because I hadn’t rebooted in a while so I tried that, but still no luck.  I searched the interwebs and found a few forum posts, but nothing too helpful.  One post included lines from /var/log/install.log so I decided to check out what mine said.

2018-03-29 22:17:47-05 macbookpro softwareupdated[501]: Scan got error The operation couldn't be completed. (NSURLErrorDomain error -1012.)
2018-03-29 22:17:47-05 macbookpro softwareupdated[501]: Ramped updates marked
2018-03-29 22:20:23-05 macbookpro softwareupdated[501]: SUScan: Scan for client pid 501 (/System/Library/CoreServices/Software
2018-03-29 22:20:23-05 macbookpro softwareupdated[501]: Failed Software Update - Refusing invalid certificate from host:
2018-03-29 22:20:23-05 macbookpro softwareupdated[501]: Failed Software Update - Refusing invalid certificate from host:
2018-03-29 22:20:23-05 macbookpro softwareupdated[501]: SUScan: Elapsed scan time = 0.2
2018-03-29 22:20:23-05 macbookpro softwareupdated[501]: SUScan: Error encountered in scan: Error Domain=NSURLErrorDomain Code=-1012 "(null)" UserInfo={NSErrorFailingURLStringKey=, NSErrorFailingURLKey=, NSLocalizedRecoverySuggestion=Make sure you’re connected to the Internet, and then try again., SUErrorRelatedCode=SUErrorCodeScanCatalogNotFound}

“Refusing invalid certificate from host:” — now we’re getting somewhere!  I knew immediately this was due to my Palo Alto decryption.  I checked my Monitor logs and confirmed that decryption was occurring on traffic to

So how do I solve this?  A little digging and I found that Palo Alto maintains a predefined list of URLs to exclude from decryption in Device -> Certificate Management -> SSL Decryption Exclusion.   These are URLs that Palo Alto knows will cause issues if decryption is attempted.  Interestingly, searching for “apple” in this list showed a number of predefined URLs.  One was even described as “apple-appstore: pinned-cert” suggesting that perhaps Apple has updated the URL for this, causing my decryption to break my update process.

To add my own, I clicked “Add” at the bottom, and entered the following.:

Committed the change and tried updating my laptop once more.  This time, it worked!