CVE-2021-22903

Severity: medium (CVSS 6.1 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 1.2% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2021-06-11 · updated 2026-06-17
Weakness: CWE-601

Description

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

Ruby on Rails: from 6.1.1 before 6.1.3.2; 6.1.0-rc2 — fixed in 6.1.3.2

How to fix

Upgrade to a fixed version: Ruby on Rails 6.1.3.2. Check the vendor advisory for mitigations.

References

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