# CVE-2021-42717: modsecurity: ModSecurity 3.x through 3.0.5 mishandles excessively nested JSON objects

CVE-2021-42717 is fixed in 3 products on 1 platform, first by DEBIAN-CVE-2021-42717, released December 7, 2021. It is not reported as exploited. Patch Radar priority: High.

- Web page: https://patchblox.com/security/cve/CVE-2021-42717
- Priority: High
- CVSS: 7.5 (high)
- EPSS: 0.0325
- CISA KEV: not listed
- Exploited (vendor report): no
- Publicly disclosed: no
- Published: Dec 7, 2021

## 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.

## Where it's fixed

| Platform | Product | Fixed in | Fix | Released |
|---|---|---|---|---|
| Linux | libapache2-mod-security2 Ubuntu 18.04.6 LTS (bionic) | 2.9.2-1ubuntu0.1~esm1 | [libapache2-mod-security2 2.9.2-1ubuntu0.1~esm1](https://patchblox.com/security/data/fix/linux/ubuntu-bionic-libapache2-mod-security2-2.9.2-1ubuntu0.1-esm1.md) | Jan 20, 2023 |
| Linux | libapache2-mod-security2 Ubuntu 20.04 LTS (focal) | 2.9.3-1ubuntu0.1 | [libapache2-mod-security2 2.9.3-1ubuntu0.1](https://patchblox.com/security/data/fix/linux/ubuntu-focal-libapache2-mod-security2-2.9.3-1ubuntu0.1.md) | Jan 20, 2023 |
| Linux | modsecurity Debian 12.15 (bookworm) | 3.0.6-1 | [DEBIAN-CVE-2021-42717](https://patchblox.com/security/data/fix/linux/debian-cve-2021-42717.md) | Dec 7, 2021 |
| Linux | modsecurity Debian 13.5 (trixie) | 3.0.6-1 | [DEBIAN-CVE-2021-42717](https://patchblox.com/security/data/fix/linux/debian-cve-2021-42717.md) | Dec 7, 2021 |
| Linux | modsecurity Debian 14 | 3.0.6-1 | [DEBIAN-CVE-2021-42717](https://patchblox.com/security/data/fix/linux/debian-cve-2021-42717.md) | Dec 7, 2021 |
| Linux | modsecurity-apache Debian 11.6 (bullseye) | 2.9.3-3+deb11u1 | [DSA-5023-1](https://patchblox.com/security/data/fix/linux/dsa-5023-1.md) | Dec 18, 2021 |
| Linux | modsecurity-apache Debian 12.15 (bookworm) | 2.9.5-1 | [DEBIAN-CVE-2021-42717](https://patchblox.com/security/data/fix/linux/debian-cve-2021-42717.md) | Dec 7, 2021 |
| Linux | modsecurity-apache Debian 13.5 (trixie) | 2.9.5-1 | [DEBIAN-CVE-2021-42717](https://patchblox.com/security/data/fix/linux/debian-cve-2021-42717.md) | Dec 7, 2021 |
| Linux | modsecurity-apache Debian 14 | 2.9.5-1 | [DEBIAN-CVE-2021-42717](https://patchblox.com/security/data/fix/linux/debian-cve-2021-42717.md) | Dec 7, 2021 |

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Data as of 2026-11-09T07:25:28Z UTC. Source: Patchblox Patch Radar (https://patchblox.com/security/patch-radar). Patchblox finds out-of-date software on Windows, macOS and Linux and updates it through release rings: https://patchblox.com/demo

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