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CVE-2021-42717

HighCVSS 7.5 / 10
Published Dec 7, 2021·Last modified Apr 16, 2026
Affected Components(0)

No affected components available

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.

Risk Scores
Base Score
7.5

The vulnerability can be exploited over the network without needing physical access. It is easy for an attacker to exploit this vulnerability. An attacker does not need any special privileges or access rights. No user interaction is needed for the attacker to exploit this vulnerability. The impact is confined to the system where the vulnerability exists. There is a high impact on the availability of the system.

Threat Intelligence
7.1

Exploitation activity has been observed. Apply available patches or mitigations urgently.

EPSS
3.21%

The exploit probability is very low. The vulnerability is unlikely to be exploited in the next 30 days.

Exploit
Proof of Concept

A proof of concept is available for this vulnerability (1 exploit found).

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