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WAF managed rules (previous version)

Managed rules, a feature of Cloudflare WAF (Web Application Firewall), identifies and removes suspicious activity for HTTP GET and POST requests.

Examples of malicious content ↗ that managed rules identify include: 

  • Common keywords used in comment spam (XX, Rolex, Viagra, etc.)
  • Cross-site scripting attacks (XSS)
  • SQL injections (SQLi)

WAF managed rules (previous version) are available to Pro, Business, and Enterprise plans for any subdomains proxied to Cloudflare. Control managed rules settings in Security > WAF > Managed rules. 

Managed rules includes three packages: 

You can use the activity log in the Security Events dashboard, available at Security > Events, to review threats blocked by WAF managed rules.

Cloudflare Managed Ruleset

The Cloudflare Managed Ruleset contains security rules written and curated by Cloudflare. Select a ruleset name under Group to reveal the rule descriptions.

Cloudflare Specials is a group that provides core firewall security against common attacks ↗.   

When viewing a ruleset, Cloudflare shows default actions for each rule listed under Default mode. The Mode available for individual rules within a specific Cloudflare Managed Ruleset are:

  • Default: Takes the default action listed under Default mode when viewing a specific rule.
  • Disable: Turns off the specific rule within the group.
  • Block: Discards the request. 
  • Interactive Challenge: The visitor receives a challenge page that requires interaction.
  • Simulate: The request is allowed through but is logged in the Activity log.

Cloudflare’s WAF changelog allows customers to monitor ongoing changes to the Cloudflare Managed Ruleset.

OWASP ModSecurity Core Rule Set

The OWASP ModSecurity Core Rule Set package assigns a score to each request based on how many OWASP rules trigger. Some OWASP rules have a higher sensitivity score than others.

After OWASP evaluates a request, Cloudflare compares the final score to the Sensitivity configured for the zone.  If the score exceeds the sensitivity, the request is actioned based on the Action configured within Package: OWASP ModSecurity Core Rule Set:

  • Block: The request is discarded.
  • Challenge: The visitor receives an interactive challenge page.
  • Simulate: The request is allowed through but is logged in the Activity log.

The sensitivity score required to trigger the WAF for a specific Sensitivity is as follows:

  • Low: 60 and higher
  • Medium: 40 and higher
  • High: 25 and higher

For AJAX requests, the following scores are applied instead:

  • Low: 120 and higher
  • Medium: 80 and higher
  • High: 65 and higher

Review the Activity log for the final score and for the individual triggered rules.

Control the OWASP package

The OWASP ModSecurity Core Rule Set package contains several rules from the OWASP project ↗. Cloudflare does not write or curate OWASP rules. Unlike the Cloudflare Managed Ruleset, specific OWASP rules are either turned On or Off.

To manage OWASP thresholds, set the Sensitivity to Low, Medium, or High under Package: OWASP ModSecurity Core Rule Set.

Setting the Sensitivity to Off will disable the entire OWASP package including all its rules. Determining the appropriate Sensitivity depends on your business industry and operations. For instance, a Low setting is appropriate for:

  • Certain business industries more likely to trigger the WAF.
  • Large file uploads. 

With a high sensitivity, large file uploads will trigger the WAF.

Cloudflare recommends initially setting the sensitivity to Low and reviewing for false positives before further increasing the sensitivity.

Important remarks

  • Managed rules introduce a limited amount of latency. 

  • Changes to WAF managed rules take about 30 seconds to update globally.

  • Cloudflare uses proprietary rules to filter traffic. 

  • Established Websockets do not trigger managed rules for subsequent requests.

  • Managed rules parse JSON responses to identify vulnerabilities targeted at APIs. JSON payload parsing is limited to 128 KB.

  • Managed rules mitigate padding techniques. Cloudflare recommends the following:

    1. Turn on rule with ID 100048. This rule protects against padding type attacks, but it is not deployed by default because there is a high probability of causing false positives in customer environments. It is, however, important that customers tune their managed rules configuration.

    2. Create a WAF custom rule using the Expression Editor depending on the need to check headers and/or body to block larger payloads (> 128 KB). Use the following fields for this purpose:

      • http.request.body.truncated
      • http.request.headers.truncated

      You should test your rule in Log mode first (if available), since the rule might generate false positives.

  • There are a handful of managed rules that Cloudflare does not disable even if you turn off Managed rules in the Cloudflare dashboard, such as rules with IDs WP0025B, 100043A, and 100030.

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