CVE-2020-8166

Ability to forge per-form CSRF tokens in Rails

It is possible to, given a global CSRF token such as the one present in the authenticity_token meta tag, forge a per-form CSRF token for any action for that session.

Impact

Given the ability to extract the global CSRF token, an attacker would be able to construct a per-form CSRF token for that session.

Workarounds

This is a low-severity security issue. As such, no workaround is necessarily until such time as the application can be upgraded.

A victim's authenticated browser session is used to submit forged requests to an application that cannot distinguish them from legitimate ones. Typical impact: state-changing actions performed as the victim without their consent.

CVE-2020-8166 has a CVSS score of 4.3 (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 (5.2.4.3, 6.0.3.1); upgrading removes the vulnerable code path.

Kodem intelligence

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1. What is CVE-2020-8166? CVE-2020-8166 is a medium-severity cross-site request forgery (CSRF) vulnerability in actionpack (rubygems), affecting versions >= 5.0.0, <= 5.2.4.2. It is fixed in 5.2.4.3, 6.0.3.1. A victim's authenticated browser session is used to submit forged requests to an application that cannot distinguish them from legitimate ones.
2. How severe is CVE-2020-8166? CVE-2020-8166 has a CVSS score of 4.3 (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-2020-8166? actionpack (rubygems) versions >= 5.0.0, <= 5.2.4.2 is affected.
4. Is there a fix for CVE-2020-8166? Yes. CVE-2020-8166 is fixed in 5.2.4.3, 6.0.3.1. Upgrade to this version or later.
5. Is CVE-2020-8166 exploitable, and should I be worried? Whether CVE-2020-8166 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-2020-8166 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-2020-8166?
   • Upgrade actionpack to 5.2.4.3 or later
   • Upgrade actionpack to 6.0.3.1 or later

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