Description
css_parser is a Ruby CSS parser. Prior to 2.1.0 and 1.22.0, the CSS Parser gem does not validate HTTPS connections, allowing a Man-in-the-Middle (MITM) attacker to inject or modify CSS content when stylesheets are loaded via HTTPS. The connection is established with OpenSSL::SSL::VERIFY_NONE, meaning any HTTPS certificate—even entirely untrusted—will be accepted without validation. This vulnerability is fixed in 2.1.0 and 1.22.0.
References5
- github.com/premailer/css_parser/commit/35e689c904225add78e0c488…
- github.com/premailer/css_parser/commit/e0c95d5abe91b237becb90ff…
- github.com/premailer/css_parser/issues/185
- github.com/premailer/css_parser/security/advisories/GHSA-ff6c-w…
- github.com/premailer/css_parser/security/advisories/GHSA-ff6c-w…
Metrics
- CVSS 3.1
-
5.8
MEDIUM
Score source: CNA
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:L/A:N - EPSS — exploit probability
- 0% percentile: 4 · as of 14 November 2026
- CWE
- CWE-295CWE-829
Could this be exploited in your environment?
A patch closes the known hole. A penetration test shows what an attacker can still reach — with proof.