Not so outdated. No Ubuntu version has the fix up to now. They think 18.04 is not affected [1]

  Ubuntu 21.10   Needed
  Ubuntu 21.04   Ignored (reached end-of-life)
  Ubuntu 20.04   Needed
  Ubuntu 18.04   Not vulnerable (code not present) 

[1] https://ubuntu.com/security/CVE-2021-4122