CVE-2023-28846

CVE-2023-28846 is a medium-severity uncontrolled resource consumption vulnerability in unpoly-rails (rubygems), affecting versions < 2.7.2.2. It is fixed in 2.7.2.2.

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Summary

unpoly-rails Denial of Service vulnerability

There is a possible Denial of Service (DoS) vulnerability in the unpoly-rails gem that implements the Unpoly server protocol for Rails applications.

Workarounds

If you cannot upgrade to a fixed release, several workarounds are available:

  • Configure your load balancer to use active health checks, e.g. by periodically requesting a route with a known response that indicates healthiness.

  • Configure your load balancer so the maximum size of response headers is at least twice the maximum size of a URL.

  • Instead of changing your server configuration you may also configure your Rails application to delete redundant X-Up-Location headers set by unpoly-rails:

    class ApplicationController < ActionController::Base

  after_action :remove_redundant_up_location_header
  
  private
  
  def remove_redundant_up_location_header
    if request.original_url == response.headers['X-Up-Location']
      response.headers.delete('X-Up-Location')
    end
  end

end

Impact

This issues affects Rails applications that operate as an upstream of a load balancer's that uses passive health checks.

The unpoly-rails gem echoes the request URL as an X-Up-Location response header. By making a request with exceedingly long URLs (paths or query string), an attacker can cause unpoly-rails to write a exceedingly large response header.

If the response header is too large to be parsed by a load balancer downstream of the Rails application, it may cause the load balancer to remove the upstream from a load balancing group. This causes that application instance to become unavailable until a configured timeout is reached or until an active healthcheck succeeds.

Crafted input forces the application to consume excessive CPU, memory, or other resources, degrading or denying service. Typical impact: denial of service.

CVE-2023-28846 has a CVSS score of 5.9 (Medium). The vector is network-reachable, no privileges required, and no user interaction. 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 (2.7.2.2); upgrading removes the vulnerable code path.

Affected versions

unpoly-rails (< 2.7.2.2)

Security releases

unpoly-rails → 2.7.2.2 (rubygems)

Kodem intelligence

Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.

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. Kodem's runtime-powered SCA identifies whether this CVE is reachable in your applications.

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Remediation advice

The fixed release 2.7.2.2+ is available via RubyGems and GitHub.

Frequently Asked Questions

  1. What is CVE-2023-28846? CVE-2023-28846 is a medium-severity uncontrolled resource consumption vulnerability in unpoly-rails (rubygems), affecting versions < 2.7.2.2. It is fixed in 2.7.2.2. Crafted input forces the application to consume excessive CPU, memory, or other resources, degrading or denying service.
  2. How severe is CVE-2023-28846? CVE-2023-28846 has a CVSS score of 5.9 (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 unpoly-rails are affected by CVE-2023-28846? unpoly-rails (rubygems) versions < 2.7.2.2 is affected.
  4. Is there a fix for CVE-2023-28846? Yes. CVE-2023-28846 is fixed in 2.7.2.2. Upgrade to this version or later.
  5. Is CVE-2023-28846 exploitable, and should I be worried? Whether CVE-2023-28846 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-2023-28846 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-2023-28846? Upgrade unpoly-rails to 2.7.2.2 or later.

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