CVE-2021-42717

Name: CVE-2021-42717
Creator: NVD / NIST
Published: 2021-12-07T22:15:06.95+00:00
License: https://creativecommons.org/publicdomain/zero/1.0/

HIGHCVSS 7.5/10EPSS 3.21%

Last modified Jun 17, 2026

CVE-2021-42717 is a high-severity vulnerability rated 7.5/10 on the CVSS scale. 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. EPSS estimates a 3.21% chance of exploitation in the next 30 days.

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.

Metrics

CVSS 3.1

7.5/10

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

EPSS Probability

3.21%

86.5th percentile

Probability of exploitation in the next 30 days. Learn more

Weakness Enumeration

CWE-674

Affected Software

Vendor	Product	Versions
Owasp	Modsecurity	>= 3.0.0, < 3.0.6
Trustwave	Modsecurity	>= 2.0.0, < 2.9.5
F5	Nginx Modsecurity Waf	r24
F5	Nginx Modsecurity Waf	r25
Debian	Debian Linux	9.0
Debian	Debian Linux	10.0
Debian	Debian Linux	11.0
Oracle	Http Server	12.2.1.3.0
Oracle	Http Server	12.2.1.4.0
Oracle	Zfs Storage Appliance Kit	8.8

References

https://lists.debian.org/debian-lts-announce/2022/05/msg00042.htmlMailing List, Third Party Advisory
https://www.debian.org/security/2021/dsa-5023Third Party Advisory
https://www.oracle.com/security-alerts/cpuapr2022.htmlPatch, Third Party Advisory
https://www.trustwave.com/en-us/resources/blogs/spiderlabs-blog/modsecurity-dos-vulnerability-in-json-parsing-cve-2021-42717/Exploit, Mitigation, Vendor Advisory
https://lists.debian.org/debian-lts-announce/2022/05/msg00042.htmlMailing List, Third Party Advisory
https://www.debian.org/security/2021/dsa-5023Third Party Advisory
https://www.oracle.com/security-alerts/cpuapr2022.htmlPatch, Third Party Advisory
https://www.trustwave.com/en-us/resources/blogs/spiderlabs-blog/modsecurity-dos-vulnerability-in-json-parsing-cve-2021-42717/Exploit, Mitigation, Vendor Advisory

Timeline

Published: Dec 7, 2021
Last Modified: Jun 17, 2026
Status: Modified

Frequently Asked Questions

What is CVE-2021-42717?

How severe is CVE-2021-42717?

CVE-2021-42717 has a CVSS score of 7.5/10 (HIGH severity). The EPSS model estimates a 3.21% probability of exploitation in the next 30 days.

How do I fix CVE-2021-42717?

Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.

Are you affected by CVE-2021-42717?

Run a free Strix scan to check your systems for this vulnerability.

Scan your code now

Source: NVD / NIST