Is this a bad certificate? (Having nine-bit long key usage extension)

Good morning,

This is part question and part potential bug report. I don't have a github
account associated with my workplace at the moment which is why I ask here.

When we tested an upgrade to rabbitmq, the tls v1.2 server rejected client
certificates with the following message: "In state certify at
ssl_handshake.erl:1975 generated SERVER ALERT: Fatal - Bad Certificate." The
issue happens with otp versions 24.0.4 and later. The earlier version 24.0.3
interoperates with the certificates successfully. After we took a closer look,
the issue has something to do with the key usage extension. If we generate a
similar certificate in all other respects but remove the key usage extension
otp does not reject the certificate. The issue also occurs without mutual
authentication as a CLIENT ALERT when an erlang/otp client validates the same
kind of server certificate.

The certificates that otp 24.0.4+ rejects were generated by gnutls certtool,
but more specifically the difference in the certificate itself is the length of
the bit string in the key usage extension. Both openssl and gnutls certtool in
their high-level text forms of the working and not working certificates show
the key usage as having the same two values of digital signature and key
encipherment. The difference underneath is that the one generated by gnutls
certtool version 3.6.9 (rejected by otp) is nine bits, value 101000000, whereas
the one generated by openssl 1.1.1f (accepted by otp) is three bits, value 101.
Both versions appear to be valid asn.1, several tools appear to see both
versions as valid certificates, and I cannot easily tell from the relevant ietf
and itu documents that either is invalid.

Below are sample certificate authority and leaf certificates that can reproduce
the issue in two local erlang/otp sessions in a typical mode of server-only
authentication with tls v1.2 during the handshake.

Is this a bug introduced in otp 24.0.4 or is this an invalid certificate?

Jesse Bickel

-- 
Contractor, ERT, Inc.
Federal Affiliation: NWC/OWP/NOAA/DOC

Sample certificate authority x.509 certificate:

-----BEGIN CERTIFICATE-----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-----END CERTIFICATE-----

Sample leaf certificate signed by above certificate authority:

-----BEGIN CERTIFICATE-----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-----END CERTIFICATE-----