What’s Vulnerable › Vulnerabilities

CVE-2026-53727: css_parser: SSRF and Local File Disclosure in `CssParser::Parser#read_remote_file`

• Severity: high (CVSS 8.6 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.5% probability of exploitation in the next 30 days
• Public exploit or detection template: yes
• Published: 2026-07-17 · updated 2026-10-24
• Weakness: CWE-918

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: 2.2.0
• Rubygems Css Parser: before 3.0.0; 0.9.0, 0.9.1, 1.0.0, 1.0.1, 1.1.1, 1.1.2 (+58) — fixed in 3.0.0

How to fix

Upgrade to a fixed version: Rubygems Css Parser 3.0.0. Check the vendor advisory for mitigations.

References

• https://github.com/premailer/css_parser/commit/7d2ddf0189cd54b54f378f59daefa10cb036e476
• https://github.com/premailer/css_parser/commit/e0a151458b2a801ae265ba420862ef8b1127b3ae
• https://github.com/premailer/css_parser/releases/tag/v3.0.0
• https://github.com/premailer/css_parser/security/advisories/GHSA-9pmc-p236-855h
• https://github.com/premailer/css_parser/security/advisories/GHSA-9pmc-p236-855h

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