Feature request: Limit the number of rules processed per request about modsecurity HOT 3 OPEN

Hi @no-sec-marko,

thanks for shared your idea.

I have had a very similar idea: monitoring a preset TX (or any custom) variable, and if it reaches the threshold, then terminate the transaction.

If you want to look up the number of triggered rules, then it's a bit problematic this way, because you must provide a method how to count the triggered rules (eg. I assume if you use CRS, you don't want to count the rules from crs-setup.conf, REQUEST-901-INITIALIZATION.conf, neither from any exclusions config).

But may be this idea can help you to reduce the number of unwanted triggering.

Please let me figure out how can we implement this, especially what would be the best way to configure these limits.

If anyone has an idea related to this feature, please share that here.

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I'm not sure that the engine should stop processing rules. In CRS, the rule for blocking based on score is one of the last rules, so stopping to process would essentially skip blocking.

However, if post-processing is the issue, then it would suffice to limit the output to audit / error logs.

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I do not really like the monitoring of a preset variable from a conceptual viewpoint.

If you want to block when a certain rule is triggered, then issue a deny with the rule.

If you want to group rules together and block afterwards, then add a rule after the group and issue a deny in this group.

I also second what @theseion stated: With a scoring rule set you can not simply stop processing and if you use ModSec to display additional information about a request in the logs in phase 5, then stopping to process a request effectively means you lack that information in the logs when you most need it.

I think this is a rules problems and it should be dealt with in the rules.

Circling back to the original reporter @no-sec-marko. Yes, this is a conceptual problem of every WAF. Given the WAF logs a ton of information it's like filling the access log of a webserver, but on steroids. You need to anticipate this when building your platform. The rule set could try to protect you, but the rule set is in a bad position to monitor its own execution and any monitoring would slow things down for the very rare case somebody tried to pull this of in the wild (I have never seen this obvious weakness being exploited).

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