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Just another day: More spam, more defences

When post is released I'll be in an exam, but I wanted to post again about the perfectly fascinating spam situation here on my blog. I've blogged about fending off spam on here before (exhibits a, b, c), but I find the problem is detecting it in a transparent manner that you as the reader don't notice very interesting, so I think I'll write another post on the subject. I could use a service like Google's ReCAPTCHA, but that would be boring :P

Recently I've had a trio of spam comments make it all the way through my (rather extensive) checks and onto my blog here. I removed them, of course, but it still baffled me as to why they made it through.

It didn't take long to find out. When I was first implementing comments on here, I added a logger specifically for purposes such as this that saves everything about current environmental state to a log file for later inspection - for both comments that make it through, and those that don't. It's not available publically available, of course (but if you'd like to take a look, just ask and I'll consider it). Upon isolating the entries for the spam comments, I discovered a few interesting things.

  • The comment keys were aged 21, 21, and 17 seconds respectively (the lower limit I have set is 10 seconds)
  • All 3 comments claimed that they were Firefox 57
  • 2 out of 3 comments used HTTP 1.0 (even though they claimed to be Firefox 57, and despite my server offering HTTP/1.1 and HTTP/2.0)
  • All 3 comments utilised HTTPS
  • The IP Addresses that the comments came form were in Ukraine, Russia, and Canada (hey?) respectively
  • All 3 appear to be phishing scams, with a link leading to a likely malicious website
  • The 2 using HTTP/1.0 also asked my server to close the connection after sending a response
  • All 3 asked not to be tracked via the DNT HTTP header
  • The last comment had some really weird capitalisation. After consulting someone experienced on the subject, I learnt that the writer likely natively spoke an eastern language, such as Chinese

This was most interesting. From this, I can conclude:

  • The last comment was likely submitted by a Chinese operator - even though the source IP address is located in Ukraine
  • All three are spoofing their user agent string.
    • Firefox 57 uses HTTP/2.0 by default if you're really in a browser, and the spam comments utilised HTTP/1.0 and HTTP/1.1
    • Curiously, all of this took place over HTTPS. I'd be really curious to log which cipher was used for the connection here.
    • In light of this, if I knew more about HTTP client libraries, I could probably identify what software was really used to submit the spam comments (and possibly even what operating system it was running on). If you know, please comment below!

To combat this development, I thought of a few options. Firstly, raising the minimum comment age, whilst effective, may disrupt the user experience, which I don't want to do. Plus, the bot owners could just increase the delay even more. To that end, I decided not to do this.

Secondly, with the amount of data I've collected, I could probably write an AI that takes the environment in and spits out a 'spaminess' score, much like SpamAssassin and rspamd do for email. Perhaps a multi-weighted system would work, with a series of tests that add or take away from the final score? I might investigate upgrading my spam detection system to do this in the future, as it would not only block spam more effectively, but provide a more distilled overview of the characteristics of each comment submission than I have currently.

Lastly, I could block HTTP/1.0 requests. While not perfect (1 out of 3 requests used HTTP/1.1), it would still catch some more bots out without disrupting user experience - as normal browsers (include text-based ones IIRC) use HTTP/1.1 or above. HTTP/1.1 has been around since 1991 (27 years!), so if you're not using it by now - upgrade! For now, this is the best option I can see.

From today, if you try to submit a comment and get a HTTP 505 HTTP Version Not Supported error and see a message saying something like this:

You sent your request via HTTP/1.0, but this is not supported for submitting comments due to high volume of spam. Please retry with HTTP/1.1 or higher.

...then you'll have to upgrade and / or reconfigure your web browser. Please let me know (my email address is on the homepage) if this causes any issues for anyone, and I'll help you out.

Found this interesting? Know more about this? Got a better solution? Comment below!

4287 Reasons why your comments weren't posted

I don't get a lot of real comments on here from what I can tell, as you've probably noticed. I don't particularly mind (though it's always awesome when I do get one!) - but what I do mind about is the spam. Since February 2015, I've gotten 4287 spam comments. 4287! It's actually quite silly, when you think about it.

The other day I was fiddling with the code behind this blog (posts about that coming soon!), and I discovered that I implemented a log ages ago that records each and every spammer, and the mistake they made - and I thought I'd share some statistics here, and some tips for dealing with spam yourself (I've posted about tactics before here.

Here's an extract from my logs (full logs available on request):

[ Sun, 02 Apr 2017 23:17:25 +0100] invalid comment | ip: 94.181.153.194 | name: ghkkll | articlepath: posts/120-Cpu-Registers.html | mistake: shortcomment
[ Mon, 03 Apr 2017 02:16:58 +0100] invalid comment | ip: 191.96.242.17 | name: exercise pants | articlepath: posts/010-Gif-Renderer.html | mistake: invalidkey
[ Mon, 03 Apr 2017 02:16:58 +0100] invalid comment | ip: 191.96.242.17 | name: exercise pants | articlepath: posts/010-Gif-Renderer.html | mistake: invalidkey
[ Mon, 03 Apr 2017 02:16:59 +0100] invalid comment | ip: 191.96.242.17 | name: exercise pants | articlepath: posts/010-Gif-Renderer.html | mistake: invalidkey
[ Mon, 03 Apr 2017 02:16:59 +0100] invalid comment | ip: 191.96.242.17 | name: exercise pants | articlepath: posts/010-Gif-Renderer.html | mistake: invalidkey

Since the output format I chose is nice and regular, I could use a quick bit of bash magic to whip up some statistics:

cat failedcomments.log | sed -e 's/^.*mistake\: //' | grep -iv '\[' | sort | uniq -c | sort -nr

(explanation, courtesy of explainshell.com )

That gave me this output:

Count Reason
3922 invalidkey
148 website
67 nokey
67 noarticleid
56 noname
17 shortcomment
4 badarticlepath
3 longcomment
2 invalidemail
1 shortname

My first thoughts here were firstly along the lines of "wow, that's a lot of spam", secondly "that comment key is working really well!", and thirdly "I didn't realise how helpful that fake website field is". Still, though I had a table, I thought a visualisation might help to put things into perspective.

A pair of pie charts showing a breakdown on which mimstakes spammers made most often. Explained below.

There - much better :D As you might have suspected if you've been following my blog here for a while, having an invalid comment key is the most common mistake spammers make.

The comment key is a hidden field in the comment form that is actually a transformed timestamp of the time you loaded the page. Working it backwards, I can work out how long it took you to submit a comment from first loading the page.

Using a companion log file to the one that I generated the above pie chart from, I've calculated that 3558 potential comments were submitted within 10 seconds of loading the page! No ordinary humans are that fast.... (especially considering you probably want to read the article before commenting!) they have to be bots. Here's a graph to illustrate the dropoff (the time is in seconds):

A graph illustrating how many bots commented on my blog unnaturally fast.

Out of the other reasons that people failed, "website" was the second most common mistake, with ~3.45% of spammers getting caught out on it. This mistake refers to another of my little spam traps - defense in depth is always good! This particular one is a regular website address hidden field, which is hidden via some fancy CSS. Curious, I decided to investigate further - and what I found was fascinating.

About 497 spammers entered an invalid website address (i.e. one that doesn't start with http) into the website box - which I really can't understand, since it's got a (hidden) label and an appropriate name and type to match - 90 of which decided that "seo plugin" was a brilliant thing to fill it with! It's important to note here that spammers who got caught by the invalid comment key filter above are included in these statistics - here's the bash command I used here:

grep -i '"website"' rawsubmits.jsonlog  | sed -e 's/^.*"website": "//' -e 's/",//' -e 's/\\\///' | uniq | egrep -iv '^http' | wc -l

Other examples include "watch live sports free", "Samantha", "just click the following web site", long strings of html-encoded unicode characters (japanese I think, after decoding one), and more. Perfectly baffling, if you ask me (if you can shed some light on this one, please comment below!).

57 spambots forgot their own name. This could be because the box you put your name in below has a name of 'name', but an id of 'namebox' - which may have caused some confusion for some of the more stupid bots.

After all that, there were 3 long comments (probably a bunch of word salad), 2 invalid email addresses that weren't caught by any filters above, and 1 short name (under 3 characters).

That's about it for this impromptu analysis of my comments log! This took far longer than I thought it would to type up. Did you find it interesting? Thinking of putting some of these techniques into practice yourself? Comment below!

Art by Mythdael