NETRESEC Network Security Blog - Tag : free

Remote Packet Dumps from PacketCache

PacketCache logo

This blog post describes how to dump a packet capture (pcap file) on a remote computer, which runs the PacketCache service, and retrieve that pcap file using only PowerShell.

PacketCache is a free Windows service that continously sniffs network traffic on all interfaces (Ethernet, WiFi, 3G, LTE etc) and maintains a cache of the most recent traffic in RAM. This enables incident responders to read PCAP data out of a PC's PacketCache, for example when an IDS or anti-virus alerts on something potentially malicious. Unfortunately, there is no central management tool for PacketCache, which means that the PCAP data has to be dumped locally at the PC that triggered the IDS or AV alert.

There are a few workarounds "hacks" available to solve this problem, but the most elegant solution is to leverage PowerShell Remoting / WinRM in order to trigger a remote PacketCache instance to create a PCAP file and then copy the PCAP file through the same PowerShell session. To make things even simpler we've created a PowerShell script that can be used to download a PCAP file from any machine running PacketCache. Okay, maybe not *any* machine, the script only works on PCs that you have admin credentails for. Nevertheless, here's how you run the script from a PowerShell prompt:

PS C:\> .\ReadRemotePacketCache.ps1 DESKTOP-LT4711 Administrator
[*] Dumping PacketCache at DESKTOP-LT4711
[*] Copying PCAP dump from DESKTOP-LT4711
[*] Remote PacketCache data saved to DESKTOP-LT4711_181112_1337.pcap
PS C:\>

The ReadRemotePacketCache.ps1 script can be downloaded from the PacketCache product page.

Configuring Hosts for PowerShell Remoting

If you have not previously set up your environment for PowerShell remoting, then you will need to follow these steps before invoking the "ReadRemotePacketCache.ps1" script as above.

On the remote PC, start PowerShell as administrator and enable PowerShell remoting with the "Enable-PSRemoting" command as shown here:

PS C:\> Enable-PSRemoting -SkipNetworkProfileCheck -Force
WinRM has been updated to receive requests.
WinRM service type changed successfully.
WinRM service started.

WinRM has been updated for remote management.
WinRM firewall exception enabled.
Configured LocalAccountTokenFilterPolicy to grant administrative rights remotely
to local users.

PS C:\>

Configuring TrustedHosts for Workgroups

You will also need to set up a trust relationship between the local and remote host. If the remote PC is member of an Active Directory domain, then this trust is already in place. However, if you're in a workgroup or the computers are not in the same domain, then you will need to set the TrustedHosts item like this on both the local PC and the remote PC:

PS C:\> Set-Item WSMan:\localhost\Client\TrustedHosts [IP or Hostname of the other PC]
PS C:\> Get-Item WSMan:\localhost\Client\TrustedHosts
PS C:\> Restart-Service WinRM

Note: if you need to dump PacketCache data from several remote hosts, then you can replace the IP/hostname with '*' to trust any PC or supply a comma separated list of individual hostnames or IPs to trust.

If you've configured TrustedHosts correctly, then you should be able to run the "ReadRemotePacketCache.ps1" script as shown previously. However, if the remote PC isn't in TrustedHosts, then you'll most likely get an error message like this:

PS C:\> .\ReadRemotePacketCache.ps1 Administrator
New-PSSession : [] Connecting to remote server failed with the following error message : The WinRM client cannot process the request. If the authentication scheme is different from Kerberos, or if the client computer is not joined to a domain, then HTTPS transport must be used or the destination machine must be added to the TrustedHosts configuration setting. Use winrm.cmd to configure TrustedHosts. Note that computers in the TrustedHosts list might not be authenticated. You can get more information about that by running the following command: winrm help config. For more information, see the about_Remote_Troubleshooting Help topic.

Automating Remote Artifact Collection

With PowerShell remoting in place you're not limited to just dumping packets from a remote PacketCache service, you can also dump the RAM or copy individual files from the remote computer. This comes in handy in order to implement an automated evidence/artifact collection, for example when a high-severity alert is received by your SIEM.

There are frameworks in place that can help with aquisition of memory and files, such as Matthew Green's Invoke-LiveResponse tool, which can dump memory with WinPMEM and leverage PowerForensics to enable remote raw disk access. Some organizations even start sniffing packets at events like this, but this will only capture the traffic from after a potential compromize. This is where PacketCache comes in, since it can allow you to retrieve packets ranging back as far as a couple of days before the alert.

Credential Theft

It is recommended to use unique passwords for each local account with administrator rights. This practice is extra important if you plan to log into a potentially compromized host using administrator credentails, as described in this blog post. You might also want to lock down the local admin accounts even further in order to minimize the consequences of the admin credentials falling into the wrong hands. See Microsoft's articles on "Local Accounts" and "Attractive Accounts for Credential Theft" for more recommendations regarding how to secure local admin accounts.

PacketCache is Free

CC BY-ND PacketCache is free to use, even commercially. It is released under a Creative Commons Attribution-NoDerivatives 4.0 International License, which means that you can copy and redistribute PacketCache in any medium or format for any purpose. You can download PacketCache here:

The PowerShell script presented in this blog post is also shared under the same CC license and can be downloaded from the PacketCache product page.


I'd like to thank Dick Svensson for suggesting the use of PowerShell Remoting to read PacketCache data remotely!

Posted by Erik Hjelmvik on Wednesday, 14 November 2018 08:00:00 (UTC/GMT)

Tags: #Netresec #PCAP #PacketCache #Windows

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CapLoader 1.6 Released

CapLoader 1.6

CapLoader is designed to simplify complex tasks, such as digging through gigabytes of PCAP data looking for traffic that sticks out or shouldn’t be there. Improved usability has therefore been the primary goal, when developing CapLoader 1.6, in order to help our users do their work even more efficiently than before.

Some of the new features in CapLoader 1.6 are:

  • Context aware selection and filter suggestions when right-clicking a flow, session or host.
  • Support for IPv6 addresses in the BPF syntax for Input Filter as well as Display Filter.
  • Flows that are inactive for more than 60 minutes are considered closed. This timeout is configurable in Tools > Settings.

Latency Measurements

CapLoader 1.6 also introduces a new column in the Flows tab labeled “Initial_RTT”, which shows the Round Trip Time (RTT) measured during the start of a session. The RTT is defined as “the time it takes for a signal to be sent plus the time it takes for an acknowledgment of that signal to be received”. RTT is often called “ping time” because the ping utility computes the RTT by sending ICMP echo requests and measuring the delay until a reply is received.

Initial RTT in CapLoader Flows Tab
Image: CapLoader 1.6 showing ICMP and TCP round trip times.

But using a PCAP file to measure the RTT between two hosts isn’t as straight forward as one might think. One complicating factor is that the PCAP might be generated by the client, server or by any device in between. If we know that the sniffing point is at the client then things are simple, because we can then use the delta-time between an ICMP echo request and the returning ICMP echo response as RTT. In lack of ping traffic the same thing can be achieved with TCP by measuring the time between a SYN and the returning SYN+ACK packet. However, consider the situation when the sniffer is located somewhere between the client and server. The previously mentioned method would then ignore the latency between the client and sniffer, the delta-time will therefore only show the RTT between the sniffer and the server.

This problem is best solved by calculating the Initial RTT (iRTT) as the delta-time between the SYN packet and the final ACK packet in a TCP three-way handshake, as shown here:

Initial Round Trip Time in PCAP Explained
Image: Initial RTT is the total time of the black/bold packet traversal paths.

Jasper Bongertz does a great job of explaining why and how to use the iRTT in his blog post “Determining TCP Initial Round Trip Time”, so I will not cover it in any more detail here. However, keep in mind that iRTT can only be calculated this way for TCP sessions. CapLoader therefore falls back on measuring the delta time between the first packet in each direction when it comes to transport protocols like UDP and ICMP.

Exclusive Features Not Available in the Free Trail

The new features mentioned so far are all available in the free 30 day CapLoader trial, which can be downloaded from our CapLoader product page (no registration required). But we’ve also added features that are only available in the commercial/professional edition of CapLoader. One such exclusive feature is the matching of hostnames against the Cisco Umbrella top 1 million domain list. CapLoader already had a feature for matching domain names against the Alexa top 1 million list, so the addition of the Umbrella list might seem redundant. But it’s actually not, the two lists are compiled using different data sources and therefore complement each other (see our blog post “Domain Whitelist Benchmark: Alexa vs Umbrella” for more details). Also, the Umbrella list contains subdomains (such as, and while the Alexa list only contains main domains (like “”). CapLoader can therefore do more fine-granular domain matching with the Umbrella list (requiring a full match of the Umbrella domain), while the Alexa list enables a more rough “catch ‘em all” approach (allowing * to be matched).

CapLoader Hosts tab with ASN, Alexa and Umbrella details

CapLoader 1.6 also comes with an ASN lookup feature, which presents the autonomous system number (ASN) and organization name for IPv4 and IPv6 addresses in a PCAP file (see image above). The ASN lookup is built using the GeoLite database created by MaxMind. The information gained from the MaxMind ASN database is also used to provide intelligent display filter CIDR suggestions in the context menu that pops up when right-clicking a flow, service or host.

CapLoader Flows tab with context menu for Apply as Display Filter
Image: Context menu suggests Display Filter BPF “net” based on the server IP in the right-clicked flow.

Users who have previously purchased a license for CapLoader can download a free update to version 1.6 from our customer portal.

Credits and T-shirts

We’d like to thank Christian Reusch for suggesting the Initial RTT feature and Daan from the Dutch Ministry of Defence for suggesting the ASN lookup feature. We’d also like to thank David Billa, Ran Tohar Braun and Stephen Bell for discovering and reporting bugs in CapLoader which now have been fixed. These three guys have received a “PCAP or it didn’t happen” t-shirt as promised in our Bug Bounty Program.

Got a t-shirt for crashing CapLoader

If you too wanna express your view of outlandish cyber attack claims without evidence, then please feel free to send us your bug reports and get rewarded with a “PCAP or it didn’t happen” t-shirt!

Posted by Erik Hjelmvik on Monday, 09 October 2017 08:12:00 (UTC/GMT)

Tags: #CapLoader #free #IPv6 #BPF #CIDR #PCAP #Umbrella #Alexa

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Keyword Search in PCAP files

Sherlock Holmes and Magnifying Glass via Inside Croydon A new function in the free version of CapLoader 1.2 is the "Find Keyword" feature. This keyword search functionality makes it possible to seek large capture files for a string or byte pattern super fast!

You might say, so what? PCAP string search can already be done with tools like tcpflow, ngrep and even Wireshark; what's the benefit of adding yet another tool to this list? One benefit is that CapLoader doesn't just give you the packet or content that matched the keyword, it will instead extract the whole TCP or UDP flow that contained the match. CapLoader also supports many different encodings, which is demonstrated in this blog post.

Here are a few quick wins with CapLoader's keyword search feature:

  • Track User-Agent - Search for a specific user agent string to extract all the HTTP traffic from a particular browser or malware.
  • Track Domain Name - Search for a particular domain name to get all DNS lookups as well as web traffic relating to that domain (including HTTP "referer" field matches).
  • Extract Messages - Search for a keyword in e-mail or chat traffic to get the whole e-mail or conversation, not just the single packet that matched.
  • Extract Files - Search for a unique string or byte sequence in a file (such as a piece of malware) to enable extraction of the complete file transfer.

EXAMPLE: DigitalCorpora M57

As an example, let's search the digital corpora file net-2009-12-06-11:59.pcap (149 MB) for the keyword "immortal". Follow these steps in order to veify our analysis using the free edition of CapLoader.

  1. Start CapLoader and select File -> Open URL, enter:
  2. Edit -> Find Keyword (or Ctrl+F), enter "immortal" CapLoader Find Keyword Form
  3. Click the "Find and Select All Matching Flows" button
  4. One TCP flow is now selected (Flow_ID 5469, -> CapLoader with one selected flow
  5. Right click the selected flow (ID 5469) and select "Flow Transcript"
CapLoader Flow Transcript of SMTP email attachment

CapLoader transcript of SMTP email flow

Looks as if an email has been sent with an attachment named "microscope1.jpg". However, the string "immortal" cannot be seen anywhere in the transcript view. The match that CapLoader found was actually in the contents of the attachment, which has been base64 encoded in the SMTP transfer in accordance with RFC 2045 (MIME).

The email attachment can easily be extracted from the PCAP file using NetworkMiner. However, to keep things transparent, let's just do a simple manual verification of the matched data. The first three lines of the email attachment are:

Decoding this with base64 gives us:
0000000: ffd8 ffe0 0010 4a46 4946 0001 0101 0090 ......JFIF......
0000010: 0090 0000 ffdb 0043 0001 0101 0101 0101 .......C........
0000020: 0101 0101 0101 0101 0101 0101 0101 0101 ................
0000030: 0101 0101 0101 0101 0101 0101 0101 0101 ................
0000040: 0101 0101 0101 0101 0101 0101 0101 0101 ................
0000050: 0101 0101 0101 0101 01ff db00 4301 0101 ............C...
0000060: 0101 0101 0101 0101 0101 0101 0101 0101 ................
0000070: 0101 0101 0101 0101 0101 0101 0101 0101 ................
0000080: 7061 7373 776f 7264 3d69 6d6d 6f72 7461 password=immorta
0000090: 6c01 0101 0101 0101 0101 0101 0101 ffc0 l...............

Tools like ngrep, tcpflow and Wireshark won't find any match for the string "immortal" since they don't support searching in base64 encoded data. CapLoader, on the other hand, supports lots of encodings.

Supported Text Encodings

CapLoader currently supports fast searching of text strings in any of the following encodings:

  • Base64 (used in email attachments and HTTP POST's)
  • DNS label encoding (RFC 1035)
  • HTML
  • Quoted Printable (used in body of email messages)
  • Unicode
  • URL encoding
  • UTF8

CapLoader also supports several local character sets, including the following code pages:

  • 437 MS-DOS Latin US
  • 850 MS-DOS Latin 1
  • 932 Japanese
  • 936 Simplified Chinese
  • 949 Korean
  • 1251 Windows Cyrillic (Slavic)
  • 1256 Windows Arabic

Having all these encodings also makes it possible to search network traffic for words like хакер, القراصنة, ハッカー, 黑客 or 해커.

The Art of War by Sun Tzu

Getting CapLoader

CapLoader is a commercial tool that also comes in a free trial edition. The search feature is available in both versions, so feel free to download CapLoader and try it your self!

CapLoader is available from the following URL:

Posted by Erik Hjelmvik on Wednesday, 02 April 2014 13:15:00 (UTC/GMT)

Tags: #search #find #keyword #flow #stream #PCAP #SMTP #transcript #free #network

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Search and Carve Packets with CapLoader 1.2

CapLoader Logo CapLoader version 1.2 was released today, with lots of new powerful features.

The most significant additions in CapLaoder 1.2 are:

  • Network packet carving, i.e. the ability to carve full content network packets from RAM dumps, disk images etc.
  • Flows can be hidden/filtered in the user interface.
  • Full content keyword search in capture files.
  • Flow can be selected based on TCP flags.
  • Better handling of broken and corrupt capture files.
What's really cool is that all these new features are available in the free version of CapLoader!

Nikon Microscope by windy_

In addition to these updates, customers using the commercial edition of CapLoader also get an updated protocol database. This update improves the Port Independent Protocol Identification (PIPI) feature in CapLoader with more protocols and better accuracy. Not only does this help analysts detect services like SSH, FTP and HTTP running on non-standard ports, but the protocol database also includes signatures for malware and APT C2 traffic like ZeroAccess, Zeus, Gh0st RAT and Poison Ivy RAT.

An update for CapLoader to version 1.2 is available for previous customers via our customer portal.

The free trial version of CapLoader can be downloaded from

CapLoader 1.2 with Transcript window
CapLoader 1.2 with suspect.pcap (from DFRWS 2008) loaded and Transcript window open

Posted by Erik Hjelmvik on Wednesday, 12 March 2014 14:45:00 (UTC/GMT)

Tags: #CapLoader #free #protocol #ZeroAccess #search #pcap

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CapLoader 1.1 Released

CapLoader Logo Version 1.1 of the super-fast PCAP parsing tool CapLoader is being released today. CapLoader is the ideal tool for digging through large volumes of PCAP files. Datasets in the GB and even TB order can be loaded into CapLoader to produce a clear view of all TCP and UDP flows. CapLoader also provides instantaneous access to the raw packets of each flow, which makes it a perfect preloader tool in order to select and export interesting data to other tools like NetworkMiner or Wireshark.

Drag-and-Drop PCAP from CapLoader to Wirehsark
Five flows being extracted from's SOTM 28 to Wireshark with CapLoader

New functionality in version 1.1

New features in version 1.1 of CapLoader are:

  • PcapNG support
  • Fast transcript of TCP and UDP flows (similar to Wireshark's ”Follow TCP Stream”)
  • Better port agnostic protocol identification; more protocols and better precision (over 100 protocols and sub-protocols can now be identified, including Skype and the C&C protocol of Poison Ivy RAT)
  • A “Hosts” tab containing a list of all transmitting hosts and information about open ports, operating system as well as Geo-IP localization (using GeoLite data created by MaxMind)
  • Gzip compressed capture files can be opened directly with CapLoader
  • Pcap files can be loaded directly from an URL

CapLoader Flow Transcript aka Follow TCP Stream
Flow transcript of Honeynet SOTM 28 pcap file day3.log

Free Trial Version

Another thing that is completely new with version 1.1 of CapLoader is that we now provide a free trial version for download. The CapLoader trial is free to use for anyone and we don't even require trial users to register their email addresses when downloading the software.

There are, of course, a few limitations in the trial version; such as no protocol identification, OS fingerprinting or GeoIP localization. There is also a limit as to how many gigabyte of data that can be loaded with the CapLoader trial at a time. This size limit is 500 GB, which should by far exceed what can be loaded with competing commercial software like Cascade Pilot and NetWitness Investigator.

The professional edition of CapLoader doesn't have any max PCAP limit whatsoever, which allows for terabytes of capture files to be loaded.

CapLoader with TCP and UDP flows view
CapLoader's Flows view showing TCP and UDP flows

CapLoader with Hosts view
CapLoader's Hosts view showing identified hosts on the network

Getting CapLoader

The trial version of CapLoader can be downloaded from the CapLoader product page. The professional edition of CapLoader can be bought at our Purchase CapLoader page.

CapLoader USB flash drive
The CapLoader USB flash drive

Customers who have previously bought CapLoader 1.0 can upgrade to version 1.1 by downloading an update from our customer portal.

For more information about CapLoader please see our previous blog post Fast analysis of large pcap files with CapLoader

Posted by Erik Hjelmvik on Monday, 21 January 2013 11:45:00 (UTC/GMT)

Tags: #CapLoader #PcapNG #PCAP #GB #gigabyte #capture #flow #transcript #free

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Recommended Books

» The Practice of Network Security Monitoring, Richard Bejtlich (2013)

» Applied Network Security Monitoring, Chris Sanders and Jason Smith (2013)

» Network Forensics, Sherri Davidoff and Jonathan Ham (2012)

» The Tao of Network Security Monitoring, Richard Bejtlich (2004)

» Practical Packet Analysis, Chris Sanders (2017)

» Windows Forensic Analysis, Harlan Carvey (2009)

» TCP/IP Illustrated, Volume 1, Kevin Fall and Richard Stevens (2011)

» Industrial Network Security, Eric D. Knapp and Joel Langill (2014)