Unprotected Alternate Channel Affecting python/cpython package, versions [,3.15.0rc2)
Threat Intelligence
The probability is the direct output of the EPSS model, and conveys an overall sense of the threat of exploitation in the wild. The percentile measures the EPSS probability relative to all known EPSS scores. Note: This data is updated daily, relying on the latest available EPSS model version. Check out the EPSS documentation for more details.
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Test your applications- Snyk IDSNYK-UNMANAGED-PYTHONCPYTHON-19651703
- published9 Sept 2026
- disclosed18 Aug 2026
- creditLukasz
Introduced: 18 Aug 2026
NewCVE-2026-15806 (opens in a new tab)How to fix?
Upgrade python/cpython to version 3.15.0rc2 or higher.
Overview
Affected versions of this package are vulnerable to Unprotected Alternate Channel through the HTTPPasswordMgr and HTTPPasswordMgrWithPriorAuth URI-matching logic in Lib/urllib/request.py. An attacker can capture stored credentials by redirecting or downgrading a client from https:// to http:// for the same host, causing credentials registered for the secure URL to be sent over cleartext HTTP. Credentials added for a URL were matched using reduce_uri() without considering the scheme, so an HTTPS credential could also be reused for an HTTP request to the same authority, and HTTP credentials could likewise be reused for HTTPS. This exposes authentication data to interception and can break applications that assume credentials are scoped to the original transport.
Workarounds
- Ensure applications never make plain
http://requests to hosts for which credentials are registered; for example, do not follow redirects tohttp://URLs. This prevents credentials from being sent over cleartext HTTP where they can be intercepted.