The OWASP CRS 4.27.0 release addresses issues with ModSecurity's reliance on content-type headers when parsing incoming requests, which previously led to false positives for API calls and form submissions. This update specifically targets rules 920240 and 920400, ensuring that the firewall evaluates actual payloads instead of depending on potentially misleading metadata. Administrators are advised to replace the old rules directory and perform a graceful server reload while keeping detection mode active to avoid disruptions. Overall, maintaining an updated rule set enhances the stability of web application firewalls by reducing false positives and minimizing the need for emergency troubleshooting

OWASP CRS 4.27.0 Update: Fix Broken Header Checks Without Breaking Your WAF

The OWASP CRS 4.27.0 release stops ModSecurity from blindly trusting content-type headers when parsing incoming requests. That single tweak kills false positives on modern API calls and form submissions that skip standard MIME markers or send messy values. Administrators should pull the updated rules, replace the old directory, and trigger a graceful server reload while leaving detection mode active for a quick sanity check. Keeping the rule set current saves hours of emergency troubleshooting and stops the firewall from accidentally blocking legitimate traffic during busy periods.

OWASP CRS 4.27.0 Update: Fix Broken Header Checks Without Breaking Your WAF @ Linux Compatible