[Bug 2018252] Re: [SRU] Fix invalid CSR version in python-acme

[Steve Langasek]

Thanks, can you provide a test plan that demonstrates (from scratch) how
to reproduce such a rejection of a CSR?

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Title:
  [SRU] Fix invalid CSR version in python-acme

Status in python-acme package in Ubuntu:
  Fix Released
Status in python-acme source package in Focal:
  Confirmed
Status in python-acme source package in Jammy:
  Incomplete

Bug description:
  [ Impact ]

  This bug causes certbot to generate CSRs which are invalid. These CSRs
  are then sent to ACME servers or otherwise parsed. Some software
  validate CSR validity more aggressively, whichmeans it will reject
  these CSRs.

  The principle motivation for backporting this fix is to stop certbot
  from generating CSRs. This will both alleviate bugs experienced by
  users, as well as reduce pressure on CSR parsers to accept _invalid_
  CSRs.

  [ Test plan ]

  The patch contains a unit test that verifies the patch itself works
  correctly. It has been present in certbot upstream since the 1.29.0
  release. Further, the fix was backported to both Debian and RHEL.
  Therefore, it has received substantial burn-in and is extremely
  unlikely to regress anything.

  [ Where problems could occur ]

  For a problem to occur, it would require software that not only
  accepted, but in fact _required_, an invalid CSR, and which also did
  not process CSRs from recent versions of certbot or versions from
  Debian or RHEL containing the backport.

  The worst-case scenario for such software would be something that
  copied the version value from a CSR into a certificate it was issuing
  (CSRs have only a single valid version, v1. X.509 certificates can be
  either v1 or v3, however in practice v3 is the only version in use.).
  Such software would end up producing different (and less
  correct/compatible) certificates. I am not aware of any software with
  this behavior.

  A more likely (though still improbable) bug would be software which
  merely asserts that the CSR's version is something incorrect.

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