URL files and WebDAV used for IcedID (Bokbot) infection

For email-based distribution, Analysts have seen OneNote files as an initial lure this month (here's one example). But these distribution patterns occasionally change. For example, on Tuesday 2023-02-21, Analysts found a distribution pattern using .url files and WebDAV traffic for an IcedID infection. On Tuesday 2023-02-21, there was a tweet about an open directory at hxxp://104.156.149.6/webdav/. Searching VirusTotal revealed at least 22 .url files that attempt to contact the server. These .url files all use file:\\ instead of http:// for the URL, and they all grab a similarly-named .bat file from the open directory. The .bat file runs a DLL installer for IcedID on the same server at \104.156.149.6webdavhost.dll. WebDAV Traffic The .url and .bat files both use WebDAV to retrieve and run the malware. WebDAV stands for "Web Distributed Authoring and Versioning," and it's a set of extensions to the HTTP protocol that allows users to access and edit files on a remote web server. You can access WebDAV servers using Windows File Explorer. This WevDAV activity generated several HTTP PROPFIND and GET requests. While GET requests are seen in almost any HTTP traffic, these PROPFIND requests are specific to WebDAV. Reviewing pcap of the IcedID infection in Wireshark, several HTTP PROPFIND requests over TCP port 80 can be found. Following TCP streams for any of the PROPFIND requests reveals a Microsoft WebDAV user agent in the request headers. The WebDAV server returns an XML file with properties of the specified directory or file. After the WebDAV activity, infection traffic was similar to previous IcedID infections. The only unusual activity was an HTTP GET request using cURL to hxxp://mandalorecnote.com/images/ caused by the .bat file. The HTTP GET request to hxxp://mandalorecnote.com/images/ returned a 12kB 64-bit DLL. This DLL doesn't appear to be used for the IcedID infection, and a cursory forensic investigation didn't find it saved to disk. It's likely a decoy file or decoy traffic, and the DLL doesn't immediately seem malicious. However, it's still an indicator for this specific wave of IcedID activity.