SSRF in Premailer CSS Parser
CVE-2026-53727
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.
Vulnerability class: SSRF (Server-Side Request Forgery)
Published · last modified .
CVSS v3 metric
CVSS v3 base score 8.6 (High). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:N/A:N.
EPSS exploit prediction
EPSS: 0.005 (42.4th percentile), scored .
Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 42nd percentile — 42.4% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.
EPSS over last 30 days · oldest: 0.005 · newest: 0.005 · change: 0.000
Affected products
- Premailer CSS Parser — versions < 3.0.0, 2.2.0
Weakness classification (CWE)
References
- github.com/premailer/css_parser/security/advisories/GHSA-9pmc-p236-855h (Exploit, Mitigation, Vendor Advisory)
- github.com/premailer/css_parser/commit/7d2ddf0189cd54b54f378f59daefa10cb036e476 (Patch)
- github.com/premailer/css_parser/commit/e0a151458b2a801ae265ba420862ef8b1127b3ae (Patch)
- github.com/premailer/css_parser/releases/tag/v3.0.0 (Product)
Frequently asked questions
- What is CVE-2026-53727?
- CVE-2026-53727 is a high-severity vulnerability in Premailer CSS Parser, classified under Server-Side Request Forgery (SSRF). CVSS score: 8.6/10. Published 2026-07-17.
- How severe is CVE-2026-53727?
- High severity. CVSS v3 base score is 8.6 out of 10.