An issue was discovered in compare_digest in Lib/hmac.py in Python through 3.9.1. Constant-time-defeating optimisations were possible in the accumulator variable in hmac.compare_digest.
Exploitability
AV:NAC:HPR:NUI:NScope
S:UImpact
C:HI:NA:N5.9/CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N