CVE-2021-22881

Actionpack Open Redirect Vulnerability

The Host Authorization middleware in Action Pack before 6.1.2.1, 6.0.3.5 suffers from an 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.

Untrusted input controls a URL used for redirection, which can forward users to attacker-controlled sites. Typical impact: phishing and credential harvesting via a trusted domain.

CVE-2021-22881 has a CVSS score of 6.1 (Medium). The vector is network-reachable, no privileges required, and user interaction required. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (6.0.3.5, 6.1.2.1); upgrading removes the vulnerable code path.

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1. What is CVE-2021-22881? CVE-2021-22881 is a medium-severity open redirect vulnerability in actionpack (rubygems), affecting versions >= 6.0.0, <= 6.0.3.4. It is fixed in 6.0.3.5, 6.1.2.1. Untrusted input controls a URL used for redirection, which can forward users to attacker-controlled sites.
2. How severe is CVE-2021-22881? CVE-2021-22881 has a CVSS score of 6.1 (Medium). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
3. Which versions of actionpack are affected by CVE-2021-22881? actionpack (rubygems) versions >= 6.0.0, <= 6.0.3.4 is affected.
4. Is there a fix for CVE-2021-22881? Yes. CVE-2021-22881 is fixed in 6.0.3.5, 6.1.2.1. Upgrade to this version or later.
5. Is CVE-2021-22881 exploitable, and should I be worried? Whether CVE-2021-22881 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
6. What actually determines whether CVE-2021-22881 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
7. How do I fix CVE-2021-22881?
   • Upgrade actionpack to 6.0.3.5 or later
   • Upgrade actionpack to 6.1.2.1 or later

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