- CVE-2026-2297: importlib: route sourceless imports through io.open_code(); FileLoader.get_data() only special-cased SourceLoader and ExtensionFileLoader, so loading a legacy .pyc via SourcelessFileLoader used a plain file object and never raised the 'open_code' audit event, leaving audit hooks unable to observe or veto the read - CVE-2026-6879: xml.etree: cache the sibling lookup in ElementPath positional predicates; the previous code rebuilt the parent's child list once per candidate element, making expressions such as './/tag[last()]' quadratic in the number of matches and giving an attacker-supplied document a CPU denial-of-service lever - CVE-2025-12781: base64: warn when b64decode() or urlsafe_b64decode() is given data containing the standard '+' or '/' characters while an alternative alphabet is in use, since those characters are silently reinterpreted rather than rejected; a malformed altchars now raises ValueError instead of tripping an assertion that vanishes under -O