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             AUSCERT External Security Bulletin Redistribution

Regular Expression Denial of Service Vunlerability of Date Parsing Methods
                             16 November 2021


        AusCERT Security Bulletin Summary

Product:           Ruby
                   date gem
Publisher:         Ruby
Operating System:  UNIX variants (UNIX, Linux, OSX)
Impact/Access:     Denial of Service -- Unknown/Unspecified
Resolution:        Patch/Upgrade
CVE Names:         CVE-2021-41817  

Original Bulletin: 

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CVE-2021-41817: Regular Expression Denial of Service Vunlerability of Date
Parsing Methods

Posted by mame on 15 Nov 2021

We have released date gem version 3.2.1, 3.1.2, 3.0.2, and 2.0.1 that include a
security fix for a regular expression denial of service vulnerability (ReDoS)
on date parsing methods. An attacker can exploit this vulnerability to cause an
effective DoS attack.


Date  s parsing methods including Date.parse are using Regexps internally, some
of which are vulnerable against regular expression denial of service.
Applications and libraries that apply such methods to untrusted input may be

The fix limits the input length up to 128 bytes by default instead of changing
the regexps. This is because Date gem uses many Regexps and it is possible that
there are still undiscovered vulnerable Regexps. For compatibility, it is
allowed to remove the limitation by explicitly passing limit keywords as nil
like Date.parse(str, limit: nil) , but note that it may take a long time to

Please update the date gem to version 3.2.1, 3.1.2, 3.0.2, and 2.0.1, or later.
You can use gem update date to update it. If you are using bundler, please add
gem "date", ">= 3.2.1" to your Gemfile .

Affected versions

  o date gem 2.0.0 or prior (which are bundled versions with Ruby 2.6 series)
  o date gem 3.0.1 or prior (which are bundled versions with Ruby 2.7 series)
  o date gem 3.1.1 or prior (which are bundled versions with Ruby 3.0 series)
  o date gem 3.2.0 or prior


Thanks to svalkanov for discovering this issue.


  o Originally published at 2021-11-15 08:00:00 (UTC)

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