CVE-2025-27220

Affected: ruby-lang CGI

In the CGI gem before 0.4.2 for Ruby, a Regular Expression Denial of Service (ReDoS) vulnerability exists in the Util#escapeElement method.

GHSA-mhwm-jh88-3gjf — CGI has Regular Expression Denial of Service (ReDoS) potential in Util#escapeElement

Affected: RubyGems: cgi

There is a possibility for Regular expression Denial of Service (ReDoS) by in the cgi gem. This vulnerability has been assigned the CVE identifier CVE-2025-27220. We recommend upgrading the cgi gem.

## Details

The regular expression used in `CGI::Util#escapeElement` is vulnerable to ReDoS. The crafted input could lead to a high CPU consumption.

This vulnerability only affects Ruby 3.1 and 3.2. If you are using these versions, please update CGI gem to version 0.3.5.1, 0.3.7, 0.4.2 or later.

## Affected versions

cgi gem versions <= 0.3.5, 0.3.6, 0.4.0 and 0.4.1.

## Credits

Thanks to svalkanov for discovering this issue. Also thanks to nobu for fixing this vulnerability.

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CVE-2025-27220

GHSA-mhwm-jh88-3gjf — CGI has Regular Expression Denial of Service (ReDoS) potential in Util#escapeElement