USN-8344-2: pip regression

USN-8344-1 fixed vulnerabilities in pip. On Ubuntu 22.04 LTS, Ubuntu 24.04 LTS,
and Ubuntu 26.04 LTS the patches for CVE-2025-66471 caused a regression when
using pip. The patches for CVE-2025-66471 have been temporarily reverted
pending investigation.

We apologize for the inconvenience.

Original advisory details:

It was discovered that pip incorrectly handled TLS certificate
verification in session connections. If a session was first used with
certificate verification disabled, subsequent requests to the same host
would also skip verification regardless of the session's current settings.
A remote attacker could possibly use this issue to perform a machine-in-the-middle
attack and expose sensitive information. (CVE-2024-35195)

It was discovered that pip's bundled urllib3 library did not limit the
number of decompression steps when processing HTTP responses. A remote
attacker could possibly use this issue to cause pip to consume excessive resources,
leading to a denial of service. (CVE-2025-66418)

It was discovered that pip's bundled urllib3 library improperly
handled streaming decompression of highly compressed data. A remote
attacker could possibly use this issue to cause pip to consume excessive resources,
leading to a denial of service. (CVE-2025-66471)