Threat Intelligence Database

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.

The css_parser Ruby gem versions prior to 2.1.0 and 1.22.0 do not validate HTTPS certificates when loading stylesheets, accepting any certificate without verification. This allows a man-in-the-middle attacker to inject or modify CSS content by exploiting the lack of HTTPS certificate validation. The vulnerability is fixed in versions 2.1.0 and 1.22.