There is a denial of service vulnerability in the header parsing component of Rack. This vulnerability has been assigned the CVE identifier CVE-2023-27539.

Versions Affected: >= 2.0.0 Not affected: None. Fixed Versions: 2.2.6.4, 3.0.6.1

Impact

Carefully crafted input can cause header parsing in Rack to take an unexpected amount of time, possibly resulting in a denial of service attack vector. Any applications that parse headers using Rack (virtually all Rails applications) are impacted.

Workarounds

Setting Regexp.timeout in Ruby 3.2 is a possible workaround.

References

• https://nvd.nist.gov/vuln/detail/CVE-2023-27539
• https://discuss.rubyonrails.org/t/cve-2023-27539-possible-denial-of-service-vulnerability-in-racks-header-parsing/82466
• https://github.com/rubysec/ruby-advisory-db/blob/master/gems/rack/CVE-2023-27539.yml
• rack/rack@231ef36
• rack/rack@ee7919e