Misleading & clumsy ModSecurity doc

[damienleger]

hello,

I'm on nginx 1.1.1 and I've been struggling with the ModSecurity documentation. I wanted to explain why since usually the doc is clean, but for ModSecurity it isn't really.

Atm on the website there are:

• [1] https://kubernetes.github.io/ingress-nginx/user-guide/third-party-addons/modsecurity/ -> entry doc for the modsecurity feature
• [2] https://kubernetes.github.io/ingress-nginx/user-guide/nginx-configuration/annotations/#modsecurity -> focus on ingress implem
• [3] https://kubernetes.github.io/ingress-nginx/user-guide/nginx-configuration/configmap/ -> focus on controller wide implem

[1] is kinda ok but miss a critical point imho: telling that there is both possible implementation: per ingress or controller wide, something that you conclude yourself by checking [2] and [3]

[2] is full of clumsy phrasing imho and mistakes, I will elaborate below

[3] there are no examples of modsecurity configmap parameters, those must be derived from their ingress annotations counterpart in [2] this is really weird. It seems like this feature is beta or something 🤨

particularly the configmap equivalent of

nginx.ingress.kubernetes.io/modsecurity-transaction-id: "$request_id"

is a bit tricky and would be interesting to detail (found how to do there

http-snippet: |- 
  modsecurity_transaction_id "$request_id";

About [2],

So if I'm rephrasing, enabling modsecurity in configmap enables it for every ingress per default except if you disable it specifically. Yet the configuration show how to enable modsecurity on ingress instead of disabling 🤨

This one is true, yet if you do that on controller level you have a ton of spam from 127.0.0.1. This tweak might be either documented or implemented by default imho.

This one I mentioned above

So I've made a lot of test to understand this one

default=y, crs=n, snippet=n

# configmap
enable-modsecurity: "true"

# /etc/nginx/nginx.conf
modsecurity on;
modsecurity_rules_file /etc/nginx/modsecurity/modsecurity.conf;

OK

default=y, crs=y, snippet=n

# configmap
enable-modsecurity: "true"
enable-owasp-modsecurity-crs: "true"

# /etc/nginx/nginx.conf
modsecurity on;
modsecurity_rules_file /etc/nginx/modsecurity/modsecurity.conf;
modsecurity_rules_file /etc/nginx/owasp-modsecurity-crs/nginx-modsecurity.conf;

OK

default=y, crs=y, snippet=y

# configmap
enable-modsecurity: "true"
enable-owasp-modsecurity-crs: "true"
modsecurity-snippet: SecRule REMOTE_ADDR "@ipMatch 127.0.0.1" "id:87,phase:1,pass,nolog,ctl:ruleEngine=Off"

# /etc/nginx/nginx.conf
modsecurity on;
modsecurity_rules '
        SecRule REMOTE_ADDR "@ipMatch 127.0.0.1" "id:87,phase:1,pass,nolog,ctl:ruleEngine=Off"
        ';
modsecurity_rules_file /etc/nginx/owasp-modsecurity-crs/nginx-modsecurity.conf;

KO! both snippet and crs are here, and doc said snippet only takes effect in that case
which clearly not the case because when trying this

# configmap
enable-modsecurity: "true"
enable-owasp-modsecurity-crs: "true"
modsecurity-snippet:-
  SecRule REMOTE_ADDR "@ipMatch 127.0.0.1" "id:87,phase:1,pass,nolog,ctl:ruleEngine=Off"
  Include /etc/nginx/owasp-modsecurity-crs/nginx-modsecurity.conf

the pod doesn't even start saying this error [emerg] 931#931: "modsecurity_rules_file" directive Rule id: 901001 is duplicated which clearly means both snippet and modsecurity_rules_file take effect here

And this last part I don't really get, the 0.24.1 instructions seem wrong since the crs doc specifically says that default conf must be loaded BEFORE crs but it's done after 🤨

And for the 0.25.0 and above if doing this and keep enable-owasp-modsecurity-crs: "true" your pod doesn't even start

What worked for me eventually is this btw.

enable-modsecurity: "true"
http-snippet: |- 
  modsecurity_transaction_id "$request_id";
modsecurity-snippet: |-
  SecRule REMOTE_ADDR "@ipMatch 127.0.0.1" "id:87,phase:1,pass,nolog,ctl:ruleEngine=Off"
  Include /etc/nginx/modsecurity/modsecurity.conf
  Include /etc/nginx/owasp-modsecurity-crs/nginx-modsecurity.conf

(btw I don't really get #8021 because I'm supposed to have this "bug" in 1.1.1, meaning I should load twice /etc/nginx/modsecurity/modsecurity.conf in the code above but it's not since pods are starting 🤨 )

What do you want to happen?

To have a better doc for the community. So that people not struggle as I did with the doc.

Is there currently another issue associated with this?

I feel like this problem of snippet/default/crs has been seen there but not entirely #8021

Does it require a particular kubernetes version?

I don't think so. I'm on EKS 1.21 (last one atm)

/kind documentation
/remove-kind feature

[k8s-ci-robot]

@damienleger: This issue is currently awaiting triage.

If Ingress contributors determines this is a relevant issue, they will accept it by applying the triage/accepted label and provide further guidance.

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[xianzheTM]

The document really confuses me.

I want to block the request with' class' in the URL. But this writing didn't take effect. So I began to wonder if I should configure every ingress.
----update----
I set each ingress and it worked. I don't understand why it can't be set in the configmap and it works for every ingress.
----update----
I saw #8021 , maybe that's why.

[arthurk]

Thanks @damienleger your comment helped me out a lot. I updated to the latest nginx-ingress helm chart version (from 4.0.9 to 4.0.19) and modescurity stopped working, using your solution made it work again.

In 4.0.9 I was using this, which worked fine:

      enable-modsecurity: true
      enable-owasp-modsecurity-crs: true
      modsecurity-snippet: |
        SecRule REMOTE_ADDR "@ipMatch 127.0.0.1" "id:87,phase:1,pass,nolog,ctl:ruleEngine=Off"

It stopped working with 4.0.19. Now I have to use:

      enable-modsecurity: true
      modsecurity-snippet: |
        SecRule REMOTE_ADDR "@ipMatch 127.0.0.1" "id:87,phase:1,pass,nolog,ctl:ruleEngine=Off"
        Include /etc/nginx/modsecurity/modsecurity.conf
        Include /etc/nginx/owasp-modsecurity-crs/nginx-modsecurity.conf

[mac-chaffee]

Apparently there's also inconsistency in which modsecurity settings take precedence when there are conflicts (owasp-modsecurity/ModSecurity-nginx#280), which undermines a lot of the assumptions of #8021. In fact, that PR broke my modsecurity settings.

To anyone else finding this thread, my advice is to just not use any of the built-in modsecurity settings. It's pretty easy to configure 100% manually:

main-snippet: "load_module /etc/nginx/modules/ngx_http_modsecurity_module.so;"
http-snippet: |
  modsecurity on;
  modsecurity_rules '
    # Yes, this does somehow take precedence over the modsecurity_rules_file below
    SecRuleEngine On
    # Put custom rules here...
  ';
  modsecurity_rules_file /etc/nginx/modsecurity/modsecurity.conf;
  modsecurity_rules_file /etc/nginx/owasp-modsecurity-crs/nginx-modsecurity.conf;

[vijay-veeranki]

Hi @damienleger @arthurk

We upgraded the chart from 4.0.19 to 4.1.1, and this configuration stopped working.

      enable-modsecurity: true
      modsecurity-snippet: |
        Include /etc/nginx/modsecurity/modsecurity.conf
        Include /etc/nginx/owasp-modsecurity-crs/nginx-modsecurity.conf

Did you try upgrading to the latest version of the chart, and see a similar issue I am facing now?

[damienleger]

Hi @vijay-veeranki . I'm afraid I cannot help you or anybody else, I decided not to use ModSecurity soon after writing this GIthub issue. I was running a PoC by then actually. Good luck with the issue you are facing.

[macmiranda]

I've tried gazillions of combinations between configMap and ingress annotations. Nothing in that documentation makes sense to me.
I get that the snippet has precedence over the owasp setting but how do you override the settings in /etc/nginx/modsecurity/modsecurity.conf?

  enable-modsecurity: "true"
  enable-owasp-modsecurity-crs: "false"
  modsecurity-snippet: |-
    SecRuleEngine On
    SecAuditEngine On
    SecAuditLogParts ABIJDEFHZ
    SecAuditLogFormat JSON
    SecAuditLogType Serial
    SecAuditLog /dev/stdout

According to the documentation I should get Audit logs in JSON format sent to the STDOUT but I keep getting same ol' /var/log/modsec_audit.log and not JSON-formated.

[mac-chaffee]

One possibility for the confusion is that updates to the modsecurity settings roll out slowly as the nginx workers restart. If there are long-lived connections keeping old nginx workers from restarting, then it can seem like changes to the modsecurity settings aren't doing anything.

But also based on this thread it sounds like there is a complex/buggy interaction between inline modsecurity settings (modsecurity-snippet) and the files (/etc/nginx/modsecurity/modsecurity.conf). I think someone has to just go look at the modsecurity-nginx source code and find out for sure what's happening.