CVE-2021-42717: Debian Linux

High severity, CVSS 7.5. EPSS: 3.2% chance of exploitation in the next 30 days.

ModSecurity 3.x through 3.0.5 mishandles excessively nested JSON objects. Crafted JSON objects with nesting tens-of-thousands deep could result in the web server being unable to service legitimate requests. Even a moderately large (e.g., 300KB) HTTP request can occupy one of the limited NGINX worker processes for minutes and consume almost all of the available CPU on the machine. Modsecurity 2 is similarly vulnerable: the affected versions include 2.8.0 through 2.9.4.

Affected products

• Debian Debian Linux: version 9.0 only; version 10.0 only; version 11.0 only
• F5 Nginx Modsecurity Waf: version r24 only; version r25 only
• Oracle HTTP Server: version 12.2.1.3.0 only; version 12.2.1.4.0 only
• Oracle ZFS Storage Appliance Kit: version 8.8 only
• Owasp Modsecurity: from 3.0.0, before 3.0.6 (fixed in 3.0.6)
• Trustwave Modsecurity: from 2.0.0, before 2.9.5 (fixed in 2.9.5)

Published 2021-12-07. Last modified 2026-06-17.