Addressing a DoS Vulnerability (CVE-2020-15598) in ModSecurity

On 14 September 2020, the OWASP ModSecurity Core Rule Set (CRS) team published details of a vulnerability in ModSecurity. The vulnerability has been assigned the identifier CVE-2020-15598, but details have not been published as of this writing. The nature of the issue is disputed by Trustwave, the maintainer of the ModSecurity project, who has proposed mitigations for the problematic behavior.

The issue can affect the NGINX Plus ModSecurity module, which is based on the current ModSecurity 3.0.4 release. The NGINX team at F5 worked with the reporter and have validated and applied their recommended update to recent releases of the NGINX Plus ModSecurity module (for NGINX Plus R20, R21, and R22).

For more details on the issue, please refer to the following resources:

OWASP CRS team: CVE-2020-15598 – ModSecurity v3 Affected By DoS (Severity HIGH)
Trustwave: ModSecurity, Regular Expressions and Disputed CVE-2020-15598
Mitre.org: CVE-2020-15598 (currently reserved, not published)

The NGINX product team at F5 is grateful to Christian Folini at NetNEA and CRS developer Ervin Hegedüs for their support to create a patch for the NGINX Plus ModSecurity module. We strongly encourage NGINX Plus subscribers to upgrade their NGINX Plus ModSecurity module to the latest version for NGINX Plus R20, R21, or R22.

Subscribers who are running versions 20-1.0.0-12, 21-1.0.1-2, or 22-1.0.1-2 or later of the nginx-plus-module-modsecurity package are protected from this issue. To confirm the installed version, you can run the following command:

Ubuntu and related platforms:

# apt list --installed nginx-plus-module-modsecurity
Listing... Done
nginx-plus-module-modsecurity/stable,now 22+1.0.1-2~focal amd64 [installed]

Red Hat Enterprise Linux and related platforms:

# yum list --installed nginx-plus-module-modsecurity
nginx-plus-module-modsecurity.x86_64  22+1.0.1-2.el8.ngx    @nginx-plus

Please reach out to your NGINX support representative at F5 if you require any assistance.

If using a private, open source build of ModSecurity, refer to the official Trustwave SpiderLabs ModSecurity repository on GitHub, consider the alternative mitigations proposed by Trustwave, and evaluate the patch provided by the OWASP CRS team. If you use ModSecurity from another source, please contact the maintainer of that source or consider the mitigations described by the OWASP CRS team and TrustWave.

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