Didier Stevens

Tuesday 28 January 2020

etl2pcapng: Support For Process IDs

Filed under: Forensics,Networking — Didier Stevens @ 0:00

You can start a packet capture on a vanilla Windows machine with command “netsh trace start capture=yes” (and end it with “netsh trace stop”).

This packet capture file, with extension .etl, can not be opened with Wireshark. Until recently, I used Microsoft’s Message Analyzer, but this tool is no longer supported and installation files have been removed from Microsoft’s site.

In comes etl2pcapng, a new open-source utility from Microsoft that converts an .etl file to .pcapng format:

Utility that converts an .etl file containing a Windows network packet capture into .pcapng format“.

I contributed to version 1.3.0 of etl2pcapng, by adding a comment containing the Process ID to each packet. etl files contain metadata (like the PID of the process associated with the network traffic) that got lost when translating to pcapng format. As the pcapng format has no option to store the PID for each packet, but it supports packet comments, I stored the PID inside packet comments:

Notice this warning by Microsoft:

The output pcapng file will have a comment on each packet indicating the PID of the current process when the packet was logged. WARNING: this is frequently not the same as the actual PID of the process which caused the packet to be sent or to which the packet was delivered, since the packet capture provider often runs in a DPC (which runs in an arbitrary process). The user should keep this in mind when using the PID information.

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