CVE-2020-5217

Directive injection when using dynamic overrides with user input

Workarounds

If you are passing user input into the above methods, you could filter out the input:

override_content_security_policy_directives(:frame_src, [user_input.gsub(";", " ")])

References

Reported in https://github.com/twitter/secure_headers/issues/418
https://www.w3.org/TR/CSP3/#parse-serialized-policy

For more information

If you have any questions or comments about this advisory:

• Open an issue in this repo
• DM @ndm on twitter

If user-supplied input was passed into append/override_content_security_policy_directives, a semicolon could be injected leading to directive injection.

This could be used to e.g. override a script-src directive. Duplicate directives are ignored and the first one wins. The directives in secure_headers are sorted alphabetically so they pretty much all come before script-src. A previously undefined directive would receive a value even if SecureHeaders::OPT_OUT was supplied.

The fixed versions will silently convert the semicolons to spaces and emit a deprecation warning when this happens. This will result in innocuous browser console messages if being exploited/accidentally used. In future releases, we will raise application errors resulting in 500s.

Duplicate script-src directives detected. All but the first instance will be ignored.

See https://www.w3.org/TR/CSP3/#parse-serialized-policy

Note: In this case, the user agent SHOULD notify developers that a duplicate directive was ignored. A console warning might be appropriate, for example.

CVE-2020-5217 has a CVSS score of 4.4 (Medium). The vector is network-reachable, low 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 (6.2.0, 5.1.0, 3.8.0); upgrading removes the vulnerable code path.

Kodem intelligence

Already deployed Kodem?

Depending on what major version you are using, the fixed versions are 6.2.0, 5.1.0, 3.8.0.

1. What is CVE-2020-5217? CVE-2020-5217 is a medium-severity security vulnerability in secure_headers (rubygems), affecting versions >= 6.0.0, < 6.2.0. It is fixed in 6.2.0, 5.1.0, 3.8.0.
2. How severe is CVE-2020-5217? CVE-2020-5217 has a CVSS score of 4.4 (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 secure_headers are affected by CVE-2020-5217? secure_headers (rubygems) versions >= 6.0.0, < 6.2.0 is affected.
4. Is there a fix for CVE-2020-5217? Yes. CVE-2020-5217 is fixed in 6.2.0, 5.1.0, 3.8.0. Upgrade to this version or later.
5. Is CVE-2020-5217 exploitable, and should I be worried? Whether CVE-2020-5217 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-2020-5217 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-2020-5217?
   • Upgrade secure_headers to 6.2.0 or later
   • Upgrade secure_headers to 5.1.0 or later
   • Upgrade secure_headers to 3.8.0 or later

Other vulnerabilities in secure_headers