CVE-2026-15806

Description

The HTTPPasswordMgr class in the urllib.request module, along with its subclasses HTTPPasswordMgrWithDefaultRealm and HTTPPasswordMgrWithPriorAuth, did not take the URL scheme into account when matching stored credentials against a requested URL. Credentials added for an https:// URL were also used for requests to the same host over http://, so an attacker able to redirect or downgrade a client to plain HTTP (for example, via an HTTPS-to-HTTP redirect or an on-path position) could capture credentials in cleartext. Credentials added for http:// URLs could likewise be sent over https://. Credential matching is now scoped by URL scheme. Credentials registered with a URL that includes a scheme are only used for requests with the same scheme. Credentials registered with a bare authority (such as example.com or example.com:8080) continue to match any scheme, preserving compatibility with existing code, including proxy authentication. Users who cannot upgrade immediately can mitigate by ensuring that applications never make plain http:// requests to hosts for which credentials are registered, for example by not following redirects to http:// URLs.

Predictions

Heuristic predictions, AS-IS, for prioritization only.

Mitigations

References

• https://github.com/python/cpython/issues/155694
• https://github.com/python/cpython/pull/155696
• https://mail.python.org/archives/list/security-announce@python.org/thread/3OKPE5S75KDNA7FY7AI3PL2MXM2X5RB3/
• https://github.com/python/cpython/commit/a0d023fbd23773e24b35d8368789470e22cda5d8
• https://github.com/python/cpython/commit/a2773a34183b7d94a243bb98fd658926cc5348ce
• https://github.com/python/cpython/commit/a7bb524fef61f77ede01f660ffbd591e1d5837ce
• http://www.openwall.com/lists/oss-security/2026/08/18/3

CWEs

CWE-319 CWE-522