#VU59052 Uncontrolled Recursion in ModSecurity - CVE-2021-42717

Vulnerability identifier: #VU59052

Vulnerability risk: Medium

CVSSv4.0: 6.6 [CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N/E:U/U:Green]

CVE-ID: CVE-2021-42717

CWE-ID: CWE-674

Exploitation vector: Network

Exploit availability: No

Vulnerable software:
ModSecurity
Server applications / IDS/IPS systems, Firewalls and proxy servers

Vendor: Trustwave

Description

The vulnerability allows a remote attacker to perform a denial of service (DoS) attack.

The vulnerability exists due to uncontrolled recursion when processing excessively nested JSON objects. A remote attacker can send a specially crafted HTTP request and consume all available worker processes and CPU resources.

Mitigation
Install updates from vendor's website.

Vulnerable software versions

ModSecurity: 2.8.0, 2.9.0 - 2.9.5, 3.0.0 - 3.0.5

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External links
https://www.trustwave.com/en-us/resources/blogs/spiderlabs-blog/modsecurity-dos-vulnerability-in-json-parsing-cve-2021-42717/

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Q & A

Can this vulnerability be exploited remotely?

Yes. This vulnerability can be exploited by a remote non-authenticated attacker via the Internet.

Is there known malware, which exploits this vulnerability?

No. We are not aware of malware exploiting this vulnerability.