Site Firewalls: ModSec

Adjusting ModSec WAF Sensitivity

The ModSec Waf can be tuned per site by adjusting two of its configuration values, the Paranoia Level and the Anomaly Threshold. This can also be done directly inside your GridPane account as well as via CLI (details below).

Setting the Paranoia Level

Adjusting the the Modsec paranoia level where {site.url} is your WordPress site’s primary domain and the paranoia level  accepts an integer from 1 to 4

gp site {site.url} -modsec -paranoia-level {1-4}

The Paranoia Level (PL) setting allows you to choose the desired level of rule checks, the least paranoid level of checking is 1 to the maximum paranoia level of 4.

With each paranoia level increase, the CRS enables additional rules giving you a higher level of security. However, higher paranoia levels also increase the possibility of blocking some legitimate traffic due to false alarms (also named false positives or FPs). If you use higher paranoia levels, it is likely that you will need to add some exclusion rules for certain requests and applications receiving complex input.

Paranoia Level 1 is default. In this level, most core rules are enabled. PL1 is advised for beginners, installations covering many different sites and applications, and for setups with standard security requirements. At PL1 you should face FPs rarely. If you encounter FPs, please open an issue on the CRS GitHub site and don’t forget to attach your complete Audit Log record for the request with the issue.

Paranoia level 2 includes many extra rules, for instance enabling many regexp-based SQL and XSS injection protections, and adding extra keywords checked for code injections. PL2 is advised for moderate to experienced users desiring more complete coverage and for installations with elevated security requirements. Setting Paranoia Level 2 will likely cause some FPs which you will need to handle.

Paranoia level 3 enables more rules and keyword lists, and tweaks limits on special characters used. PL3 is aimed at users experienced at the handling of FPs and at installations with a high-security requirement.

Paranoia level 4 further restricts special characters. The highest level is advised for experienced users protecting installations with very high security requirements. Running PL4 will likely produce a very high number of FPs which have to be treated before the site can go production live.

Rules in paranoia level 2 or higher will log their PL to the audit log. This allows you to deduct from the audit log how the WAF behavior is affected by the increased paranoia level. for example:

[tag "paranoia-level/2"]

Setting the Anomaly Threshold

Adjusting the the Modsec paranoia level where {site.url} is your WordPress site’s primary domain and the paranoia level  accepts an integer.

gp site site.com -modsec -anomaly-threshold {integer}

The anomaly threshold is where you can specify at which cumulative anomaly score an inbound request, or outbound response, gets blocked. Most detected inbound threats will give a critical score of 5.

Smaller violations, like violations of protocol/standards, carry lower scores.

GridPane Default anomaly threshold is set to a value of 10, this means a request would require at least two critical alerts or a combination of many lesser alerts to reach the blocking threshold.

You can adjust this to suit your needs or while tuning the firewall for your site. Setting this value to 5 would result in the firewall blocking any request that gives a single critical score, while a value of 7 would require a critical score plus a smaller violation.

You can increase your threshold to allow for a less secure firewall, however in such circumstances some attacks may bypass the CRS rules or your own configured policies. Having said that it is a common practice to start a fresh CRS installation with elevated anomaly scoring thresholds (>100) and then lower the limits as your confidence in the setup grows.

Anomaly Threshold / Paranoia Level Quadrant