CVE-2019-16254: HTTP response splitting in WEBrick (Additional fix)

There is an HTTP response splitting vulnerability in WEBrick bundled with Ruby. This vulnerability has been assigned the CVE identifier CVE-2019-16254.


If a program using WEBrick inserts untrusted input into the response header, an attacker can exploit it to insert a newline character to split a header, and inject malicious content to deceive clients.

This is the same issue as CVE-2017-17742. The previous fix was incomplete, which addressed the CRLF vector, but did not address an isolated CR or an isolated LF.

All users running an affected release should upgrade immediately.

Affected Versions

  • All releases that are Ruby 2.3 or earlier
  • Ruby 2.4 series: Ruby 2.4.7 or earlier
  • Ruby 2.5 series: Ruby 2.5.6 or earlier
  • Ruby 2.6 series: Ruby 2.6.4 or earlier
  • Ruby 2.7.0-preview1
  • prior to master commit 3ce238b5f9795581eb84114dcfbdf4aa086bfecc


Thanks to znz for discovering this issue.


  • Originally published at 2019-10-01 11:00:00 (UTC)