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Vulnerability record · CVE-2021-42717 · published 7 December 2021

CVE-2021-42717: Owasp modsecurity vulnerability

Owasp · Modsecurity

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.

7.5 CVSS 3.1 High EPSS 3.1% · top 12.6% CWE-674 · CWE-674
7.5CVSS 3.1 base score, v2 5.0
3.1%EPSS exploitation probability, 30 days
NoNot in CISA KEV
6Affected product versions listed by NVD
8References, 2 tagged exploit
17 Jun 2026Last modified by NVD

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.

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Affected products

6 vulnerable configurations from NVD's CPE data, grouped by vendor and product.

References

LinkTags
https://lists.debian.org/debian-lts-announce/2022/05/msg00042.html Mailing ListThird Party Advisory
https://www.debian.org/security/2021/dsa-5023 Third Party Advisory
https://www.oracle.com/security-alerts/cpuapr2022.html PatchThird Party Advisory
https://www.trustwave.com/en-us/resources/blogs/spiderlabs-blog/modsecurity-dos-vulnerability-in-json-parsing-cve-2021-4 ExploitMitigationVendor Advisory
https://lists.debian.org/debian-lts-announce/2022/05/msg00042.html Mailing ListThird Party Advisory
https://www.debian.org/security/2021/dsa-5023 Third Party Advisory
https://www.oracle.com/security-alerts/cpuapr2022.html PatchThird Party Advisory
https://www.trustwave.com/en-us/resources/blogs/spiderlabs-blog/modsecurity-dos-vulnerability-in-json-parsing-cve-2021-4 ExploitMitigationVendor Advisory

Track CVE-2021-42717 inside VULONE

Watch it alongside the ransomware crews, C2 infrastructure and forum chatter that reference it, query it through the API and pull it into your SIEM over TAXII.

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Same products first, then exploited flaws of the same weakness class.

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Source: NIST National Vulnerability Database (record CVE-2021-42717), CISA KEV, FIRST EPSS (scores of 2026-09-28). This page is refreshed as NVD updates the record.