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  5. CVE-2026-44312

CVE-2026-44312: CSS Parser: Improper Certificate Validation allows MITM injection of remote CSS content

May 7, 2026 (updated May 8, 2026)

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.

References

  • github.com/advisories/GHSA-ff6c-w6qf-7xqc
  • github.com/premailer/css_parser
  • github.com/premailer/css_parser/commit/35e689c904225add78e0c488cf04bad052666449
  • github.com/premailer/css_parser/commit/e0c95d5abe91b237becb90ff316531a6547ada18
  • github.com/premailer/css_parser/issues/185
  • github.com/premailer/css_parser/security/advisories/GHSA-ff6c-w6qf-7xqc
  • nvd.nist.gov/vuln/detail/CVE-2026-44312

Code Behaviors & Features

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Affected versions

All versions before 1.22.0, all versions starting from 2.0.0 before 2.1.0

Fixed versions

  • 2.1.0
  • 1.22.0

Solution

Upgrade to versions 1.22.0, 2.1.0 or above.

Impact 5.8 MEDIUM

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

Learn more about CVSS

Weakness

  • CWE-295: Improper Certificate Validation
  • CWE-829: Inclusion of Functionality from Untrusted Control Sphere

Source file

gem/css_parser/CVE-2026-44312.yml

Spotted a mistake? Edit the file on GitLab.

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