BREW-asciidoctor-CVE-2026-53727 — Ruby CSS Parser: SSRF and Local File Disclosure in `CssParser::Parser#read_remote_file`

Affected: Homebrew: asciidoctor

## Summary

`CssParser::Parser#read_remote_file` (and therefore `load_uri!`, and the `@import`-following branch of `add_block!`) issues HTTP/HTTPS requests against any host, port and URI it is handed, with no scheme allowlist, no host / IP filtering, and no protection against link-local, loopback or RFC‑1918 addresses. `Location:` redirects are followed recursively back into the same function, which **also services `file://` URIs**, so a single attacker-controlled HTTP redirect upgrades the bug from SSRF to arbitrary local file disclosure.

In practice, any consumer of `css_parser` that hands it attacker‑influenced CSS together with a `base_uri:` option — Premailer being the canonical example — is exposed. The attacker only needs the ability to land one `@import url(...)` in the CSS that the host application parses.

## Vulnerable code

[`lib/css_parser/parser.rb#L613-L687`](https://github.com/premailer/css_parser/blob/cee10f16b11dd175f17b0e5f6aefa488378e964b/lib/css_parser/parser.rb#L613-L687):

```ruby def read_remote_file(uri) # :nodoc: ... begin uri = Addressable::URI.parse(uri.to_s)

if uri.scheme == 'file' # local file path = uri.path path.gsub!(%r{^/}, '') if Gem.win_platform? src = File.read(path, mode: 'rb') # <-- arbitrary local read else # remote file if uri.scheme == 'https' uri.port = 443 unless uri.port http = Net::HTTP.new(uri.host, uri.port) http.use_ssl = true else…

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

Affected: premailer css_parser

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.

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BREW-asciidoctor-CVE-2026-53727 — Ruby CSS Parser: SSRF and Local File Disclosure in `CssParser::Parser#read_remote_file`

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