CVE-2021-42717

HIGH

OWASP ModSecurity 2.8.0-2.9.4 and 3.0.0-3.0.5 - Denial of Service via Excessively Nested JSON Objects

Title source: llm
STIX 2.1

Exploitation Summary

EIP tracks 1 public exploit for CVE-2021-42717. PoCs published by EkamSinghWalia.

AI-analyzed exploit summary This repository contains a detection and mitigation script for CVE-2021-42717, a ModSecurity DoS vulnerability in JSON parsing. The script checks for the presence of ModSecurity and its configuration to determine vulnerability and applies mitigation by adjusting the SecRequestBodyNoFilesLimit setting.

Description

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.

Exploits (1)

nomisec SCANNER
by EkamSinghWalia · poc
https://github.com/EkamSinghWalia/Detection-and-Mitigation-script-for-CVE-2021-42717

This repository contains a detection and mitigation script for CVE-2021-42717, a ModSecurity DoS vulnerability in JSON parsing. The script checks for the presence of ModSecurity and its configuration to determine vulnerability and applies mitigation by adjusting the SecRequestBodyNoFilesLimit setting.

Classification
Scanner 90%
Attack Type
Dos
Complexity
Trivial
Reliability
Reliable
Target: ModSecurity 2.8.0 through 2.9.4 and 3.x through 3.0.5
No auth needed
Prerequisites: ModSecurity installed on the system · Access to modify modsecurity.conf
devstral-2 · analyzed Feb 16, 2026 Full analysis →

References (4)

Core 4
Core References
Third Party Advisory vendor-advisory x_refsource_debian
https://www.debian.org/security/2021/dsa-5023
Patch, Third Party Advisory x_refsource_misc
https://www.oracle.com/security-alerts/cpuapr2022.html
Mailing List, Third Party Advisory mailing-list x_refsource_mlist
https://lists.debian.org/debian-lts-announce/2022/05/msg00042.html

Scores

CVSS v3 7.5
EPSS 0.0321
EPSS Percentile 86.5%
Attack Vector NETWORK
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Details

CWE
CWE-674
Status published
Products (10)
debian/debian_linux 9.0
debian/debian_linux 10.0
debian/debian_linux 11.0
f5/nginx_modsecurity_waf r24
f5/nginx_modsecurity_waf r25
oracle/http_server 12.2.1.3.0
oracle/http_server 12.2.1.4.0
oracle/zfs_storage_appliance_kit 8.8
owasp/modsecurity 3.0.0 - 3.0.6
trustwave/modsecurity 2.0.0 - 2.9.5
Published Dec 07, 2021
Tracked Since Feb 18, 2026