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Fencer Vulns
medium 5.8

CVE-2026-44312 json

css_parser allows to MITM included https css urls

published 2026-05-07 6 mo ago modified 2026-10-26 14 d ago also EUVD-2026-30330 , GHSA-ff6c-w6qf-7xqc

cvss
5.8
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.1%
EPSS 0.1% chance of exploitation in 30 days, percentile 3%
public exploits
0
none known

Summary

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.

Patch / fix

  • rubygems css_parser 1.22.0, 2.1.0
  • premailer css_parser 1.22.0, 2.1.0
  • ruby-css-parser Debian 12 1.6.0-2+deb12u1
  • ruby-css-parser Debian 13 1.19.0-1+deb13u1
  • ruby-css-parser Debian 14 2.1.0-1

debian advisories DEBIAN-CVE-2026-44312

Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2026-44312 updated cvss 5.8

css_parser: css_parser: Man-in-the-Middle attack due to improper HTTPS certificate validation

  • Red Hat 3scale API Management Platform 2 3scale-amp21/system, 3scale-amp22/system, 3scale-amp2/system-rhel7, 3scale-amp2/system-rhel8, 3scale-amp2/system-rhel9
    affected: no fix available “Fix deferred”

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

CISA SSVC

Exploitation
Proof of concept is public
Automatable
yes
Technical impact
partial
Assessed
5 mo ago

Exploit prediction

0.15% chance of exploitation in the next 30 days, higher than 3% of all scored CVEs (FIRST EPSS, 2026-11-08).

Exploits and checks

  • github.com https://github.com/premailer/css_parser/security/advisories/GHSA-ff6c-w6qf-7xqc referenced PoC, tagged "exploit" by a source, unverified

CVSS scores

assigned by version score vector
CNA 3.1 5.8 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:L/A:N
GitHub 3.1 5.8 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:L/A:N

Affected packages

ecosystem package affected fixed in
rubygems css_parser
>=2.0.0, <2.1.0
<1.22.0
2.1.0
1.22.0

Affected products

  • premailer css_parser

Classification

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

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.

CPEs and fixed versions use Anchore's correction of NVD's data: Added CPE configurations because not yet analyzed by NVD.