High [CVE-2026-53727] Arbitrary local file disclosure via Server-Side Request Forgery
This high-severity Red Hat Linux advisory covers CVE-2026-53727.
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Summary
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. A flaw was found in css_parser from 2.2.0 before 3.0.0.
CssParser::Parser#read_remote_file (used by load_uri! and @import handling in add_block!) issues HTTP/HTTPS requests without host, IP, or scheme restrictions, including to loopback and RFC1918 targets, and recursively follows Location redirects.
Those redirects can land on file:// URIs, turning SSRF into arbitrary local file disclosure when an application passes attacker-influenced CSS with a base_uri option. css_parser is vulnerable to SSRF in remote stylesheet loading.
- < 2.2.0
- < 3.0.0
Official advisory · high-confidence parse· fetched 6 days ago·verify at source
Mitigation
Upgrade to a fixed release: 3.0.0. That is the remediation for this advisory.
The vendor advisory may list interim mitigations or workarounds not captured here. Review it before change work.
Official advisory · high-confidence parse· fetched 6 days ago·verify at source
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