USN-5821-4: pip regression

USN-5821-3 fixed a vulnerability in pip. The update introduced
a minor regression in Ubuntu 14.04 ESM, Ubuntu 16.04 ESM and
Ubuntu 18.04 LTS. This update fixes the problem.

We apologize for the inconvenience.

Original advisory details:

Sebastian Chnelik discovered that wheel incorrectly handled
certain file names when validated against a regex expression.
An attacker could possibly use this issue to cause a
denial of service.

advisory denial of service file fixes issue lts names pip problem regex service ubuntu update usn vulnerability