A Ruby security update has been released for Ubuntu Linux 16.04 LTS, 18.04 LTS, 20.04 LTS, and 20.10.

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Ubuntu Security Notice USN-4922-1
April 20, 2021

ruby2.3, ruby2.5, ruby2.7 vulnerability
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A security issue affects these releases of Ubuntu and its derivatives:

- Ubuntu 20.10
- Ubuntu 20.04 LTS
- Ubuntu 18.04 LTS
- Ubuntu 16.04 LTS

Summary:

Ruby incorrectly handled XML documents.

Software Description:
- ruby2.7: Object-oriented scripting language
- ruby2.5: Object-oriented scripting language
- ruby2.3: Object-oriented scripting language

Details:

Juho Nurminen discovered that the REXML gem bundled with Ruby incorrectly
parsed and serialized XML documents. A remote attacker could possibly use
this issue to perform an XML round-trip attack.

Update instructions:

The problem can be corrected by updating your system to the following
package versions:

Ubuntu 20.10:
libruby2.7 2.7.1-3ubuntu1.3
ruby2.7 2.7.1-3ubuntu1.3

Ubuntu 20.04 LTS:
libruby2.7 2.7.0-5ubuntu1.4
ruby2.7 2.7.0-5ubuntu1.4

Ubuntu 18.04 LTS:
libruby2.5 2.5.1-1ubuntu1.9
ruby2.5 2.5.1-1ubuntu1.9

Ubuntu 16.04 LTS:
libruby2.3 2.3.1-2~ubuntu16.04.16
ruby2.3 2.3.1-2~ubuntu16.04.16

In general, a standard system update will make all the necessary changes.

References:
  https://ubuntu.com/security/notices/USN-4922-1
CVE-2021-28965

Package Information:
  https://launchpad.net/ubuntu/+source/ruby2.7/2.7.1-3ubuntu1.3
  https://launchpad.net/ubuntu/+source/ruby2.7/2.7.0-5ubuntu1.4
  https://launchpad.net/ubuntu/+source/ruby2.5/2.5.1-1ubuntu1.9
  https://launchpad.net/ubuntu/+source/ruby2.3/2.3.1-2~ubuntu16.04.16