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.
References (4)
Core 4
Core References
X_Refsource_Confirm x_refsource_confirm
https://github.com/premailer/css_parser/security/advisories/GHSA-ff6c-w6qf-7xqc
X_Refsource_Misc x_refsource_misc
https://github.com/premailer/css_parser/issues/185
X_Refsource_Misc x_refsource_misc
https://github.com/premailer/css_parser/commit/35e689c904225add78e0c488cf04bad052666449
X_Refsource_Misc x_refsource_misc
https://github.com/premailer/css_parser/commit/e0c95d5abe91b237becb90ff316531a6547ada18
Scores
CVSS v3
5.8
EPSS
0.0002
EPSS Percentile
6.2%
Attack Vector
NETWORK
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:L/A:N
CISA SSVC
Vulnrichment
Exploitation
poc
Automatable
yes
Technical Impact
partial
Details
CWE
CWE-295
CWE-829
Status
published
Products (4)
premailer/css_parser
< 1.22.0
premailer/css_parser
>= 2.0.0, < 2.1.0
rubygems/css_parser
0 - 1.22.0RubyGems
rubygems/css_parser
2.0.0 - 2.1.0RubyGems
Published
May 14, 2026
Tracked Since
May 14, 2026