CVE-2026-44312
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.
Does this matter?
Lower severity and a low EPSS score (0.15%). Track it; it rarely justifies an emergency change on its own.
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.
- CVSS 3.1
- 5.8 MEDIUMCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:L/A:N
- EPSS
- 0.15% probability · 4th percentile
- CISA KEV
- Not listed
- Weakness
- CWE-295, CWE-829
- Source
- security-advisories@github.com
References
- https://github.com/premailer/css_parser/commit/35e689c904225add78e0c488cf04bad052666449
- https://github.com/premailer/css_parser/commit/e0c95d5abe91b237becb90ff316531a6547ada18
- https://github.com/premailer/css_parser/issues/185
- https://github.com/premailer/css_parser/security/advisories/GHSA-ff6c-w6qf-7xqc
- https://github.com/premailer/css_parser/security/advisories/GHSA-ff6c-w6qf-7xqc
Source: NVD record, EPSS from FIRST.org, KEV from CISA. Refreshed daily.