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HIGH

CVE-2021-42717

CVSS v3

7.5

HIGH

EPSS Score

3.2 %

exploit probability, as of 2026-10-19

CISA KEV

No

known exploited

Exploitation

—

SSVC status

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Affected and fixed versions

Packages from OSV.dev and products from the vendors' CSAF advisories.

version not verifiedVersions not verified: read as OSV.dev and the vendors publish them, not checked against each vendor's release list.

Packages

  • modsecurityBitnamifrom 2.0.0 · fixed in 2.9.5and 1 other package

Vendor advisories

  • CVE-2021-42717 Red Hat Product Security

    libmodsecurity: crafted JSON objects with nesting could result in the web server being unable to service legitimate requests

Full record on 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.

Technical details

Published
2021-12-07

Frequently asked questions

What is CVE-2021-42717?

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.

Is CVE-2021-42717 actively exploited?

Active exploitation of CVE-2021-42717 has not been confirmed. Its EPSS score was 3.2% on 2026-10-19, the estimated probability of exploitation in the next 30 days.

What is the CVSS score for CVE-2021-42717?

CVE-2021-42717 has a CVSS v3 base score of 7.5 (HIGH severity).

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