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 Details

CVSS Score

5.8

Severity

MEDIUM

CVSS Vector

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

Configurations (Affected Products)

No configuration data available.

css_parser < 2.1.0

css_parser < 1.22.0

PoC / Exploit Code

⚠ For Security Research Only

The following code is for security research and authorized testing only.

python

# Ruby PoC to demonstrate the vulnerability in css_parser < 2.1.0
# This script shows that the parser loads content from a URL with an invalid SSL certificate.

require 'css_parser'

# A URL with a self-signed or expired certificate (e.g., badssl.com)
target_url = 'https://expired.badssl.com/'

parser = CssParser::Parser.new

puts "Attempting to load CSS from: #{target_url}"
puts "Note: This site has an expired certificate and should fail in a secure environment."

begin
  # In vulnerable versions, this succeeds because VERIFY_NONE is used
  parser.load_uri!(target_url)
  puts "[VULNERABLE] Successfully loaded CSS despite invalid certificate!"
  puts "Loaded Rules Count: #{parser.rules.length}"
rescue => e
  puts "[SAFE/ERROR] Connection failed as expected: #{e.message}"
end

References

[1] CVE.org https://www.cve.org/CVERecord?id=CVE-2026-44312
[2] NVD NIST https://nvd.nist.gov/vuln/detail/CVE-2026-44312
[3] CVE Details https://www.cvedetails.com/cve/CVE-2026-44312/
[4] VulDB https://vuldb.com/cve/CVE-2026-44312
[5] https://github.com/premailer/css_parser/commit/35e689c904225add78e0c488cf04bad052666449
[6] https://github.com/premailer/css_parser/commit/e0c95d5abe91b237becb90ff316531a6547ada18
[7] https://github.com/premailer/css_parser/issues/185
[8] https://github.com/premailer/css_parser/security/advisories/GHSA-ff6c-w6qf-7xqc

Raw JSON Data

JSON

{"cve": {"id": "CVE-2026-44312", "sourceIdentifier": "[email protected]", "published": "2026-05-14T17:16:22.393", "lastModified": "2026-05-14T18:13:33.660", "vulnStatus": "Deferred", "cveTags": [], "descriptions": [{"lang": "en", "value": "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."}], "metrics": {"cvssMetricV31": [{"source": "[email protected]", "type": "Secondary", "cvssData": {"version": "3.1", "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:L/A:N", "baseScore": 5.8, "baseSeverity": "MEDIUM", "attackVector": "NETWORK", "attackComplexity": "LOW", "privilegesRequired": "NONE", "userInteraction": "NONE", "scope": "CHANGED", "confidentialityImpact": "NONE", "integrityImpact": "LOW", "availabilityImpact": "NONE"}, "exploitabilityScore": 3.9, "impactScore": 1.4}]}, "weaknesses": [{"source": "[email protected]", "type": "Primary", "description": [{"lang": "en", "value": "CWE-295"}, {"lang": "en", "value": "CWE-829"}]}], "references": [{"url": "https://github.com/premailer/css_parser/commit/35e689c904225add78e0c488cf04bad052666449", "source": "[email protected]"}, {"url": "https://github.com/premailer/css_parser/commit/e0c95d5abe91b237becb90ff316531a6547ada18", "source": "[email protected]"}, {"url": "https://github.com/premailer/css_parser/issues/185", "source": "[email protected]"}, {"url": "https://github.com/premailer/css_parser/security/advisories/GHSA-ff6c-w6qf-7xqc", "source": "[email protected]"}]}}