Vulnerability · Published Jul 17, 2026 · Assigned by GitHub_M
CVE-2026-53727css_parser: SSRF and Local File Disclosure in `CssParser::Parser#read_remote_file`
High 8.9
In plain English
A high-severity server-side request forgery in css_parser from premailer. Proof-of-concept exploit code is public. The chance it is exploited in the next 30 days is estimated at 0.5% (higher than 43% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.
Official 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 packages & fixed versions
| Ecosystem | Package | Fixed in | Advisory |
|---|---|---|---|
| Debian:12 | ruby-css-parser | no fix listed | DEBIAN-CVE-2026-53727 |
| Debian:13 | ruby-css-parser | no fix listed | DEBIAN-CVE-2026-53727 |
| Debian:14 | ruby-css-parser | 3.0.0-1 | DEBIAN-CVE-2026-53727 |
| RubyGems | css_parser | 3.0.0 | GHSA-9pmc-p236-855h |
| Ubuntu:22.04:LTS | ruby-css-parser | no fix listed | UBUNTU-CVE-2026-53727 |
| Ubuntu:24.04:LTS | ruby-css-parser | no fix listed | UBUNTU-CVE-2026-53727 |
| Ubuntu:26.04:LTS | ruby-css-parser | no fix listed | UBUNTU-CVE-2026-53727 |
| Ubuntu:26.10 | ruby-css-parser | no fix listed | UBUNTU-CVE-2026-53727 |
Affected products (as reported)
| Vendor | Product | Versions |
|---|---|---|
| premailer | css_parser | < 3.0.0 |
Weakness: CWE-918 · Vector: 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
References
- https://github.com/premailer/css_parser/security/advisories/GHSA-9pmc-p236-855h x_refsource_CONFIRM
- https://github.com/premailer/css_parser/commit/7d2ddf0189cd54b54f378f59daefa10cb036e476 x_refsource_MISC
- https://github.com/premailer/css_parser/commit/e0a151458b2a801ae265ba420862ef8b1127b3ae x_refsource_MISC
- https://github.com/premailer/css_parser/releases/tag/v3.0.0 x_refsource_MISC