ModSecurity Audit Logs Showing Numeric Severity Instead of String Defined in Rules and Incorrect Severity Mapping

owasp-modsecurity / ModSecurity

ModSecurity is an open source, cross platform web application firewall (WAF) engine for Apache, IIS and Nginx. It has a robust event-based programming language which provides protection from a range of attacks against web applications and allows for HTTP traffic monitoring, logging and real-time analysis.

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ModSecurity Audit Logs Showing Numeric Severity Instead of String Defined in Rules and Incorrect Severity Mapping #3271

Open rohithmulka opened 1 week ago

rohithmulka commented 1 week ago

I'm encountering an issue where the severity in ModSecurity audit logs is shown as a numeric value (e.g., "severity": "2") instead of the string defined in the rules (e.g., "severity": "CRITICAL")

0: EMERGENCY 1: ALERT 2: CRITICAL 3: ERROR 4: WARNING 5: NOTICE 6: INFO 7: DEBUG

Issue: Rules like 949110 (blocking evaluation) do not have a defined severity, but in the logs, severity = 0 is being incorrectly mapped to "EMERGENCY", causing confusion.

audit_log.json

airween commented 6 days ago

Hi @rohithmulka,

thanks for bringing this up.

Yes, this is a known behavior of libmodsecurity3 (I read your message on Slack, this is why I know - but it would be good to fill the issue template with versions and other information).

I think we have to discuss here (with other libmodsecurity3 users) what would be the correct behavior. I think we can modify the code that if a rule does not have a severity action then that field won't be in the log. But I don't know how users would be happy, eg. if someone uses an own parser which expects the field...

theseion commented 4 days ago

I feel like "no severity" should mean "default log level", which I assume would be DEBUG.

airween commented 1 day ago

I feel like "no severity" should mean "default log level", which I assume would be DEBUG.

I think there are more different aspects around the severity rule value.

first that @rohithmulka brought up: if a rule does not have severity action, then why the engines log it with any value?
second that you mention @theseion: if there is no severity, then how should we interpret that?
- I think the best would be that we don't write that into the log
third: how the engine behaves in this case? In case of libmodsecurity3 + Nginx, severity value determines which rules must appear in the log. Eg. if the Nginx's log level is "lower" than info then only rules will be logged which have CRITICAL value (if I'm not wrong)
- maybe this implicit 0 is there because Nginx needs to know to logging. I haven't inspected that yet.

So we definitely have some works with this.