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CrowdSec vs Fail2Ban - What to use?

Hey all, i've decided I should probably setup something else to help block nefarious IP addresses. I've been looking into CrowdSec and Fail2Ban but i'm not really sure the best one to use.

My setup is OpnSense -> Nginx Proxy Manager -> Servers. I think I need to setup CrowdSec/Fail2Ban on the Nginx Proxy Manager to filter the access logs, then ideally it would setup the blocks on OpnSense - but i'm not sure that can be done?

Any experience in a setup like this? I've found a few guides but some of them seem fairly outdated.

Edit: thanks everybody for the great info. General consensus seems to be with crowdsec so I'll go down that path and see how it goes.

Edit 2: So after having it up and running for the better part of a day, i'm going to remove it again. For some reason there was a performance impact loading websites, probably because it was waiting for a response from the Crowdsec hub? Either way, after stopping it from running everything is back to normal again. So I might revisit how I do it and probably try Fail2Ban now instead. Thanks everybody

51 comments
  • I actually refrain from using Crowdsec since we found ourselves with a friend banning each other for no known reasons. (I swear I'm a good boy)

    • As you probably know the crowdsec bouncer doesn't directly parse logs or do checks like F2B filters. It queries the crowdsec LAPI for decisions and applies them. The “allowed” or “whitelisted” IP logic is handled at the Security Engine or LAPI level, not by the bouncer itself.

      You can whitelist an ip in /etc/crowdsec/whitelists.yaml or even whitelist decisions in the whitelist.yaml as such:

       
          
      name: private-ips
      description: Whitelist local and private IPs
      whitelist:
        reason: "Allow local and private IPs"
        ip:
          - "127.0.0.1"
          - "192.168.1.0/24"
        cidr:
          - "10.0.0.0/8"
      
        

      Then issue sudo systemctl reload crowdsec. Kind of the same concept as F2B's ignoreip option. If you are using Tailscale to administer the server, then it's easier to whitelist. IIRC, you can use cscli decisions add --type whitelist --ip 192.168.1.100 --duration 1y but it doesn't add them to the whitelist.yaml. Instead it keeps them in crowdsec's database managed by LAPI. To undo: cscli decisions delete --ip 192.168.1.100 --type whitelist

      https://docs.crowdsec.net/u/getting_started/post_installation/whitelists/

      • With the bouncer setup, I assume I need to pass in where to look for logs or something for those to be passed into the lapi? I followed this CrowdSec and Nginx Proxy Manager , as far as I can tell everything is connected an running, I have crowdsec running on OpnSense via the plugin - it appears to be healthy as per the CrowdSec Console.

         
            
        npm  | [nginx       ] nginx: [error] [lua] crowdsec.lua:62: init(): error loading captcha plugin: no recaptcha site key provided, can't use recaptcha       
        npm  | [nginx       ] nginx: [error] [lua] ban.lua:37: new(): BAN_TEMPLATE_PATH and REDIRECT_LOCATION variable are empty, will return HTTP 403 for ban decisions
        npm  | [nginx       ] nginx: [alert] [lua] crowdsec_openresty.conf:5):11: [Crowdsec] Initialisation done                                                    
        npm  | [supervisor  ] starting service 'app'...                                                                                                             
        npm  | [app         ] [5/5/2025] [11:26:30 PM] [Global   ] › ℹ  info      Using Sqlite: /data/database.sqlite                                               
        npm  | [supervisor  ] all services started.
        
        
          
    • Care to elaborate? This seems kind of insanely specific.

      Also, if you're using fail2ban, the same thing would happen.

      • I don't have much to elaborate on ^^' but yeah, could have been an hyper specific case but that was my experience with it. I assumed my ip was banned on the crowd or something like that and even if my friend unbanned me twice, the ban came back. Don't know what really happened for sure.

  • From the guy that has been accused of going overboard on security measures, I use both. It just depends on your setup tho. On a low resource server, I would pick crowdsec as it covers more ground than F2B. Running two log parsers does use more resources. ~ my 2 cents

  • Crowdsec is much more efficient than fail2ban. Fail2ban is a lot of old single-threaded Python code with inefficient log parsing/tailing routines. Crowdsec is a more modern Go codebase.

    If you're looking at old-school solutions, there's also DenyHosts.

  • Fail2ban unless you need the features that crowdsec provides. They are different tools with different purposes and different features.

    • I thought crowdsec does everything fail2ban does in addition to global block lists?

      • Fail2ban is a Free/Open-Source program to parse logs and take action based on the content of these logs. The most common use case is to detect authentication failures in logs and issue a firewall level ban based on that. It uses regex filters to parse the logs and policies called jails to determine which action to take (wait for more failures, run command xyz...). It's old, basic, customizable, does its job.

        crowdsec is a commercial service [1] with a free offering, and some Free/Open-Source components. The architecture is quite different [2], it connects to Crowdec's (the company) servers to crowd-source detections, their service establishes a "threat score" for each IP based on detections they receive, and in exchange they provide [3] some of these threat feeds/blocklists back to their users. A separate crowdsec-bouncer process takes action based on your configuration.

        If you want to build your own private shared/global blocklist based on crowdsec detections, you'll need to setup a crowdsec API server and configure all your crowdsec instances to use it. If you want to do this with fail2ban you'll need to setup your own sync mechanism (there are multiple options, I use a cron job+script that pulls IPs from all fail2ban instances using fail2ban-client status, builds an ipset, and pushes it to all my servers). If you need crowdsourced blocklists, there are multiple free options ([4] can be used directly by ipset).

        Both can be used for roughly the same purpose, but are very different in how they work and the commercial model (or lack of) behind the scenes.

  • I'm currently going through a similar situation at the moment (OPNSense firewall, Traefik reverse proxy). For my solution, I'm going to be trial running the Crowdsec bouncer as a Traefik middleware, but that shouldn't discourage you from using Fail2Ban.

    Fail2Ban: you set policies (or use presets) to tempban IPs that match certain heuristic or basic checks.

    Crowdsec Bouncer: does fail2ban checks if allowed. Sends anonymous bad behavior reports to their servers and will also ban/captcha check IPs that are found in the aggregate list of current bad actors. Claims to be able to perform more advanced behavior checks and blacklists locally.

    If you can help it, I don't necessarily recommend having OPNSense apply the firewall rules via API access from your server. It is technically a vulnerability vector unless you can only allow for creating a certain subset of deny rules. The solution you choose probably shouldn't be allowed to create allow rules on WAN for instance. In most cases, let the reverse proxy perform the traffic filtering if possible.

    • I did have that same thought actually, with opening up opnsense to be modified. But I also like the idea of it getting blocked before it even gets into my network, instead if letting it in initially and then blocking afterwards - that's kinda the whole job of a firewall after all ha ha

51 comments