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Denial of Service Vulnerability in Action View

High severity GitHub Reviewed Published Mar 13, 2019 to the GitHub Advisory Database • Updated Nov 9, 2023

Package

bundler actionview (RubyGems)

Affected versions

>= 5.1.0, <= 5.1.6.1
>= 5.0.0, <= 5.0.7.1
>= 4.0.0, <= 4.2.11.0
>= 5.2.0, <= 5.2.2.0
>= 6.0.0.beta1, < 6.0.0.beta3

Patched versions

5.1.6.2
5.0.7.2
4.2.11.1
5.2.2.1
6.0.0.beta3

Description

Denial of Service Vulnerability in Action View

Impact

Specially crafted accept headers can cause the Action View template location code to consume 100% CPU, causing the server unable to process requests. This impacts all Rails applications that render views.

All users running an affected release should either upgrade or use one of the workarounds immediately.

Releases

The 6.0.0.beta3, 5.2.2.1, 5.1.6.2, 5.0.7.2, and 4.2.11.1 releases are available at the normal locations.

Workarounds

This vulnerability can be mitigated by wrapping render calls with respond_to blocks. For example, the following example is vulnerable:

class UserController < ApplicationController 
  def index 
    render "index" 
  end 
end 

But the following code is not vulnerable:

class UserController < ApplicationController 
  def index 
    respond_to |format| 
      format.html { render "index" } 
    end 
  end 
end 

Implicit rendering is impacted, so this code is vulnerable:

class UserController < ApplicationController 
  def index 
  end 
end 

But can be changed this this:

class UserController < ApplicationController 
  def index 
    respond_to |format| 
      format.html { render "index" } 
    end 
  end 
end 

Alternatively to specifying the format, the following monkey patch can be applied in an initializer:

$ cat config/initializers/formats_filter.rb 
# frozen_string_literal: true 

ActionDispatch::Request.prepend(Module.new do 
  def formats 
    super().select do |format| 
      format.symbol || format.ref == "*/*" 
    end 
  end 
end) 

Please note that only the 5.2.x, 5.1.x, 5.0.x, and 4.2.x 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.

Also note that the patches for this vulnerability are the same as CVE-2019-5418.

Credits

Thanks to John Hawthorn john@hawthorn.email of GitHub

References

Published to the GitHub Advisory Database Mar 13, 2019
Published by the National Vulnerability Database Mar 27, 2019
Reviewed Jun 16, 2020
Last updated Nov 9, 2023

Severity

High

CVSS overall score

This score calculates overall vulnerability severity from 0 to 10 and is based on the Common Vulnerability Scoring System (CVSS).
/ 10

CVSS v3 base metrics

Attack vector
Network
Attack complexity
Low
Privileges required
None
User interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
None
Availability
High

CVSS v3 base metrics

Attack vector: More severe the more the remote (logically and physically) an attacker can be in order to exploit the vulnerability.
Attack complexity: More severe for the least complex attacks.
Privileges required: More severe if no privileges are required.
User interaction: More severe when no user interaction is required.
Scope: More severe when a scope change occurs, e.g. one vulnerable component impacts resources in components beyond its security scope.
Confidentiality: More severe when loss of data confidentiality is highest, measuring the level of data access available to an unauthorized user.
Integrity: More severe when loss of data integrity is the highest, measuring the consequence of data modification possible by an unauthorized user.
Availability: More severe when the loss of impacted component availability is highest.
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

EPSS score

0.282%
(69th percentile)

CVE ID

CVE-2019-5419

GHSA ID

GHSA-m63j-wh5w-c252

Source code

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