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Detecting a tracker pixel/image in email (infosec.pub)

submitted 7 months ago* (last edited 7 months ago) by coffeeClean@infosec.pub to c/cybersecurity@infosec.pub

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An HTML-only email from a gov agency has a logo referencing an URL that looks like this:

https://1wy1y.mjt.lu/tplimg/1wy1y/f/l9hl7/g3q3v.png

It’s not exactly that (apart from the domain) but of course it’s rather unique looking. They send email routinely. The initial emails had an obviously non-suspicious basic logo, like “(their office domain)/files/logo.png”. But then later they switched and every message from them is the URL in the mjt.lu domain. It’s not unique per message but it could be unique to the user, perhaps to keep tabs on when each person reads their messages.

The output of torsocks curl -LI looks like this:

HTTP/2 200
date: (exactly now)
content-type: image/png
accept-ranges: bytes

That’s it. It’s the shortest HTTP header I’ve seen. There’s no content-length. I find that suspicious because if this is a service that facilitates tracker pixels, then they would want to withhold the length in order to dodge detection. Although from its usage in my case it wouldn’t just be a pixel -- it’s a logo.

The date is also suspect. Shouldn’t the date be the date of the object, not the current time this second?

Are there any other checks to investigate this?

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[–] coffeeClean@infosec.pub 4 points 7 months ago* (last edited 7 months ago) (1 children)

What does referencing mean exactly?

Sometimes HTML email comes with the logos and objects needed to render it, sometimes not. When the objects are included it’s possible to render the message while offline. In the case at hand, the logo was not included and the HTML body defined a logo with that unique URL inside img tags.

In the very least, if we assume the tracking is appropriate and that it’s consistent with the privacy policy and ToS I agreed to, I would still find it objectionable that a government would conceal the fact that they are using a tracker pixel/image by withholding the content-length header. The gov should be transparent about what they are doing. They should even disclose in each such message “we have a tracker pixel in here”, for transparency which should not be an issue if it’s legit. I personally need the content-length header because I’m on a shit internet connection and have a need to know how big something is before I fetch it. So I’m disturbed that all Cloudflare sites (which is like ½ the web now) withhold the content-length header. The agency at hand is sloppy with privacy and probably sloppy with everything. It’s not necessarily malicious but nonetheless I’m not going to lower the standard by which they should be held to.

[–] stevedidwhat_infosec@infosec.pub 2 points 7 months ago

Right right, I know how html tags and all that works just wanted to make sure we were for sure both talking about the same thing that’s all. Wasn’t verbiage I normally see so I verified quick

And this 2nd part you have here makes total sense with me and I fully agree, just wanted to make sure I wouldn’t be inadvertently causing any harm to you if you were struggling with paranoia or anything like that, that’s all. Hope I wasn’t coming off as too dismissive!!