File upload rules bypass in OWASP ModSecurity Core Rule Set (CRS)

1) Input validation error

EUVDB-ID: #VU72099

Risk: Medium

CVSSv3.1: 4.6 [CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N/E:U/RL:O/RC:C]

CVE-ID: CVE-2019-13464

CWE-ID: CWE-20 - Improper input validation

Exploit availability: No

Description

The vulnerability allows a remote attacker to bypass filtration rules.

The vulnerability exists due to an error when using X.Filename instead of X_Filename in some PHP Script Uploads rules, because PHP automatically transforms dots into underscores in certain contexts where dots are invalid. A remote attacker can bypass implemented rules and successfully upload dangerous files on the server.

Mitigation

Install updates from vendor's website.

Vulnerable software versions

OWASP ModSecurity Core Rule Set (CRS): 3.0.0 - 3.1.2

External links

http://github.com/SpiderLabs/owasp-modsecurity-crs/issues/1386
http://github.com/SpiderLabs/owasp-modsecurity-crs/pull/1391

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.