[Security] Bump waitress from 1.4.2 to 1.4.3

[dependabot-preview]

Bumps waitress from 1.4.2 to 1.4.3.

Changelog

Sourced from waitress's changelog.

1.4.3 (2020-02-02)

Security Fixes

- In Waitress version 1.4.2 a new regular expression was added to validate the
  headers that Waitress receives to make sure that it matches RFC7230.
  Unfortunately the regular expression was written in a way that with invalid
  input it leads to catastrophic backtracking which allows for a Denial of
  Service and CPU usage going to a 100%.
This was reported by Fil Zembowicz to the Pylons Project. Please see
GHSA-73m2-3pwg-5fgc
for more information.

Commits

• cbc89bf Prep v1.4.3
• 6e46f9e Merge pull request from GHSA-73m2-3pwg-5fgc
• 51b9bd4 Remove accidental backslash
• f87abb7 Add bad header that caused catastrophic backtracking
• 2fe8e54 Add header parsing tests with short headers
• ac0ca05 Remove catastrophic backtracking in regex
• See full diff in compare view

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[dependabot-preview]

We've just been alerted that this update fixes a security vulnerability:

Sourced from The GitHub Security Advisory Database.

Critical severity vulnerability that affects waitress

Impact

When waitress receives a header that contains invalid characters it will cause the regular expression engine to catastrophically backtrack causing the process to use 100% CPU time and blocking any other interactions.

This would allow an attacker to send a single request with an invalid header and take the service offline.

Invalid header example:

Bad-header: xxxxxxxxxxxxxxx\x10
... (truncated)

Affected versions: ["= 1.4.2"]