Description
css_parser is a Ruby CSS parser. From 2.2.0 until 3.0.0, CssParser::Parser#read_remote_file in lib/css_parser/parser.rb, and therefore load_uri! and the @import-following branch of add_block!, issued HTTP and HTTPS requests against any host, port, and URI without a scheme allowlist, host or IP filtering, or protection against link-local, loopback, or RFC-1918 addresses. Location: redirects were followed recursively back into the same function, which also serviced file:// URIs, so a single attacker-controlled HTTP redirect could upgrade the bug from SSRF to arbitrary local file disclosure. Any consumer of css_parser that hands it attacker-influenced CSS together with a base_uri: option is exposed. This issue is fixed in version 3.0.0.
Affected products
premailer: css parser
References5
- github.com/premailer/css_parser/security/advisories/GHSA-9pmc-p… ExploitMitigationVendor Advisory
- github.com/premailer/css_parser/security/advisories/GHSA-9pmc-p… ExploitMitigationVendor Advisory
- github.com/premailer/css_parser/commit/7d2ddf0189cd54b54f378f59… Patch
- github.com/premailer/css_parser/commit/e0a151458b2a801ae265ba42… Patch
- github.com/premailer/css_parser/releases/tag/v3.0.0 Product
Metrics
- CVSS 3.1
-
8.6
HIGH
Score source: NVD
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:N/A:N - CVSS 4.0
-
8.9
HIGH
Score source: CNA
CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:H/VI:N/VA:N/SC:H/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X - EPSS — exploit probability
- 1% percentile: 44 · as of 14 November 2026
- CWE
- CWE-918
Could this be exploited in your environment?
A patch closes the known hole. A penetration test shows what an attacker can still reach — with proof.