CVE-2020-5267

Cross site scripting vulnerability in ActionView

ActionView::Helpers::JavaScriptHelper::JS_ESCAPE_MAP.merge!(
  {
    "`" => "\\`",
    "$" => "\\$"
  }
)

module ActionView::Helpers::JavaScriptHelper
  alias :old_ej :escape_javascript
  alias :old_j :j

  def escape_javascript(javascript)
    javascript = javascript.to_s
    if javascript.empty?
      result = ""
    else
      result = javascript.gsub(/(\\|<\/|\r\n|\342\200\250|\342\200\251|[\n\r"']|[`]|[$])/u, JS_ESCAPE_MAP)
    end
    javascript.html_safe? ? result.html_safe : result
  end

  alias :j :escape_javascript
end

There is a possible XSS vulnerability in the j and escape_javascript methods in ActionView. These methods are used for escaping JavaScript string literals. Impacted code will look something like this:

<script>let a = `<%= j unknown_input %>`</script>

or

<script>let a = `<%= escape_javascript unknown_input %>`</script>

CVE-2020-5267 has a CVSS score of 4.8 (Medium). The vector is network-reachable, high 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 (5.2.4.2, 6.0.2.2); upgrading removes the vulnerable code path.

Kodem intelligence

Already deployed Kodem?

To aid users who aren't able to upgrade immediately we have provided patches for
the two supported release series. They are in git-am format and consist of a
single changeset.

• 5-2-js-helper-xss.patch - Patch for 5.2 series
• 6-0-js-helper-xss.patch - Patch for 6.0 series

Please note that only the 5.2 and 6.0 series are supported at present. Users
of earlier unsupported releases are advised to upgrade as soon as possible as we
cannot guarantee the continued availability of security fixes for unsupported
releases.

1. What is CVE-2020-5267? CVE-2020-5267 is a medium-severity security vulnerability in actionview (rubygems), affecting versions <= 5.2.4.1. It is fixed in 5.2.4.2, 6.0.2.2.
2. How severe is CVE-2020-5267? CVE-2020-5267 has a CVSS score of 4.8 (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 actionview are affected by CVE-2020-5267? actionview (rubygems) versions <= 5.2.4.1 is affected.
4. Is there a fix for CVE-2020-5267? Yes. CVE-2020-5267 is fixed in 5.2.4.2, 6.0.2.2. Upgrade to this version or later.
5. Is CVE-2020-5267 exploitable, and should I be worried? Whether CVE-2020-5267 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-2020-5267 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-2020-5267?
   • Upgrade actionview to 5.2.4.2 or later
   • Upgrade actionview to 6.0.2.2 or later

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