CVE-2021-42717
HIGHEPSS 87th pctlDescription
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.
How to fix
TridentStack Control can deploy fixes like this automatically across your Windows, macOS, and Linux fleet. See how it works
Remediation is compiled from vendor and distribution security advisories. Always confirm against the linked source for your exact version and platform.
CVSS v3 Vector
Exploitability
Impact
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Exploit Intelligence
Elevated risk: more likely to be exploited than 87% of all known CVEs.
References
Related Vulnerabilities
Other CWE-674 vulnerabilities, ordered by exploit likelihood. View all
| CVE | Severity | CVSS | EPSS | Exploited | Fix |
|---|---|---|---|---|---|
| CVE-2021-45105 | Medium | 5.9 | 100% | - | Fix |
| CVE-2024-25111 | High | 8.6 | 65% | - | Fix |
| CVE-2023-50269 | High | 8.6 | 58% | - | Fix |
| CVE-2021-42697 | High | 7.5 | 36% | - | Fix |
| CVE-2018-0739 | Medium | 6.5 | 19% | - | Fix |
| CVE-2007-1285 | High | 7.5 | 18% | - | Fix |
Common questions
How do I fix CVE-2021-42717?
Published advisories record a fix for 4 affected products. The "How to fix" section on this page lists the fixed version and source advisory for each one, so apply the entry matching what you actually run.
Is CVE-2021-42717 being actively exploited?
Not that we know of. CVE-2021-42717 is not in the CISA Known Exploited Vulnerabilities catalog. Its EPSS score of 3.2% is the estimated probability that it will be exploited in the next 30 days. That is higher than 87% of all scored CVEs.
How severe is CVE-2021-42717?
CVE-2021-42717 has a CVSS v3 base score of 7.5, rated high. CVSS rates the technical impact if the vulnerability is exploited, not how likely that is, so weigh it alongside the exploit-prediction score when you decide what to patch first.
What does CVE-2021-42717 affect?
Published advisories record a fix for modsecurity (Debian), libapache2-mod-security2 (Ubuntu), libapache2-modsecurity (Ubuntu), modsecurity-apache (Ubuntu). Only products with a sourced advisory are listed, so treat this as what we can cite rather than a complete inventory.
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This product uses NVD data but is not endorsed or certified by the NVD. EPSS scores courtesy of FIRST.org (https://www.first.org/epss). Source: CISA KEV Catalog. Data as of 2025-07-03.