Arch Linux ASA-201411-16 Moderate: Ruby Denial Service Exploit

Arch Linux Security Advisory ASA-201411-16
=========================================
Severity: Medium
Date    : 2014-11-17
CVE-ID  : CVE-2014-8090
Package : ruby
Type    : denial of service
Remote  : Yes
Link    : https://wiki.archlinux.org/title/CVE-2014

Summary
======
The package ruby before version 2.1.5-1 is vulnerable to denial service
through unrestricted XML entity expansion.

Resolution
=========
Upgrade to 2.1.5-1.

# pacman -Syu "ruby>=2.1.5-1"

The problem has been fixed upstream in version 2.1.5.

Workaround
=========
If you cannot upgrade Ruby, use this monkey patch as a workaround:

class REXML::Document
  def document
    self
  end
end

Description
==========
CPU exhaustion can occur as a result of recursive expansion with an
empty string. When reading text nodes from an XML document, the REXML
parser can be coerced into allocating extremely large string objects
which can consume all of the memory on a machine, causing a denial of
service.

Impact
=====
A remote attacker using an specially crafted XML document is able to
perform denial of service through CPU and/or memory exhaustion.

References
=========
https://www.ruby-lang.org/en/news/2014/11/13/rexml-dos-cve-2014-8090/
https://access.redhat.com/security/cve/CVE-2014-8090