An issue was discovered in Python before 3.11.1. An unnecessary quadratic algorithm exists in one path when processing some inputs to the IDNA (RFC 3490) decoder, such that a crafted, unreasonably long name being presented to the decoder could lead to a CPU denial of service. Hostnames are often supplied by remote servers that could be controlled by a malicious actor; in such a scenario, they could trigger excessive CPU consumption on the client attempting to make use of an attacker-supplied supposed hostname. For example, the attack payload could be placed in the Location header of an HTTP response with status code 302. A fix is planned in 3.11.1, 3.10.9, 3.9.16, 3.8.16, and 3.7.16.
https://security.netapp.com/advisory/ntap-20221209-0007/
https://security.gentoo.org/glsa/202305-02
https://lists.debian.org/debian-lts-announce/2023/06/msg00039.html
https://lists.debian.org/debian-lts-announce/2023/05/msg00024.html