CVE-2026-15806: `HTTPPasswordMgr` can send saved HTTPS credentials via HTTP because of incorrect scheme matching
HTTPPasswordMgr can send saved HTTPS credentials via HTTP because of incorrect scheme matching
Other sources
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.
— MITRE
Affected Software
Remediation
Recommended actions to resolve this vulnerability, in priority order.
- Upgrade
Upgrade to a fixed release to a version that resolves this vulnerability.
Fixed in 3.12.14-2 - Configuration
Update Python so HTTPPasswordMgr/its subclasses scope saved credentials to requests with the same URL scheme; credentials registered with an https:// URL must only be used for https:// requests, and http:// credentials must only be used for http:// requests.
Python urllib.request.HTTPPasswordMgr / HTTPPasswordMgrWithDefaultRealm / HTTPPasswordMgrWithPriorAuth Credential matching by URL scheme = enabled (scope credentials to same URL scheme only) - Configuration
As an immediate mitigation, ensure applications do not make plain http:// requests to hosts for which credentials are registered; specifically, do not follow HTTPS-to-HTTP redirects to http:// URLs.
Application HTTP client behavior Redirect handling (HTTPS -> HTTP) = do not follow redirects to http:// URLs for credentialed hosts
Event History
Frequently Asked Questions
Under what conditions could credentials be exposed?
Applications using HTTPPasswordMgr, HTTPPasswordMgrWithDefaultRealm, or HTTPPasswordMgrWithPriorAuth are exposed when they register credentials against an https:// URL and can be redirected or downgraded to http:// on the same host. An on-path attacker or a server-controlled HTTPS-to-HTTP redirect could cause the credentials to be sent in cleartext.
Are all stored credentials affected by the scheme-matching change?
The issue affects scheme-qualified credential registrations: credentials stored for https://host could be reused for http://host before the fix. Credentials registered with a bare authority, such as example.com or example.com:8080, intentionally continue to match requests using any scheme.
What can be done if an upgrade is not immediately possible?
Prevent applications from making plain http:// requests to any host for which credentials are registered, including by refusing to follow redirects to http:// URLs. This avoids the downgrade path that could transmit HTTPS credentials over HTTP.