CVE-2026-44312

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 v3.1 Score

5.8

MEDIUM

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:L/A:N

EPSS — Exploit Prediction

0.0002

Probability of exploitation

0.06%

Percentile rank

EPSS estimates the probability that this vulnerability will be exploited in the wild within the next 30 days. A higher score means more likely to be exploited.

Weakness Type (CWE)

CWE-295 CWE-295

CWE-829 CWE-829

References

Other 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

Frequently Asked Questions

What is CVE-2026-44312? +

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. It has a CVSS v3.1 base score of 5.8 (MEDIUM).

How severe is CVE-2026-44312? +

CVE-2026-44312 has a CVSS v3.1 score of 5.8 out of 10, rated MEDIUM. This is a medium-severity vulnerability that should be remediated as part of regular maintenance. The EPSS score is 0.0002, placing it in the 0th percentile for exploitation probability.

How do I check if I'm vulnerable to CVE-2026-44312? +

You can use Secably's free Website Scanner to check your website for known vulnerabilities. For infrastructure scanning, use the Port Scanner to identify exposed services that may be affected. Check the vendor advisories linked above for specific patch and version information.

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