CVE-2021-22903: Rubyonrails Rails

Medium severity, CVSS 6.1. EPSS: 1.2% chance of exploitation in the next 30 days.

The actionpack ruby gem before 6.1.3.2 suffers from a possible open redirect vulnerability. Specially crafted Host headers in combination with certain "allowed host" formats can cause the Host Authorization middleware in Action Pack to redirect users to a malicious website. This is similar to CVE-2021-22881. Strings in config.hosts that do not have a leading dot are converted to regular expressions without proper escaping. This causes, for example, `config.hosts << "sub.example.com"` to permit a request with a Host header value of `sub-example.com`.

Affected products

• Rubyonrails Rails: from 6.1.1, before 6.1.3.2 (fixed in 6.1.3.2); version 6.1.0 only

Published 2021-06-11. Last modified 2026-06-17.