CPython 3.9 and earlier doesn't disallow configuring an empty list ("[]") for SSLContext.set_npn_protocols() which is an invalid value for the underlying OpenSSL API. This results in a buffer over-read when NPN is used (see CVE-2024-5535 for OpenSSL). This vulnerability is of low severity due to NPN being not widely used and specifying an empty list likely being uncommon in-practice (typically a protocol name would be configured).
Exploitability
AV:NAC:LPR:NUI:NScope
S:UImpact
C:LI:NA:L6.5/CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:L