Credential disclosure via cross-scheme auth matching
Published Aug 18, 2026 · Updated Aug 21, 2026
Credential disclosure in urllib.request in CPython before 3.15.0 allows attackers to read HTTP auth credentials via cross-scheme requests. HTTPPasswordMgr, HTTPPasswordMgrWithDefaultRealm, and HTTPPasswordMgrWithPriorAuth reduce stored and requested URLs without preserving the scheme, so credential lookup and prior-auth matching can treat https:// and http:// on the same host as the same protection space. Exploitation requires an HTTPS-to-HTTP redirect, an on-path downgrade, or application logic that makes plain HTTP requests for a host with saved credentials; the public proof of concept shows an Authorization header added to an HTTP request before any server response.
Summary
What happened
Credential disclosure in urllib.request in CPython before 3.15.0 allows attackers to read HTTP auth credentials via cross-scheme requests. HTTPPasswordMgr, HTTPPasswordMgrWithDefaultRealm, and HTTPPasswordMgrWithPriorAuth reduce stored and requested URLs without preserving the scheme, so credential lookup and prior-auth matching can treat https:// and http:// on the same host as the same protection space. Exploitation requires an HTTPS-to-HTTP redirect, an on-path downgrade, or application logic that makes plain HTTP requests for a host with saved credentials; the public proof of concept shows an Authorization header added to an HTTP request before any server response.
The record
- CVE
- CVE-2026-15806
- Published
- Aug 18, 2026
- Updated
- Aug 21, 2026
- Vendor
- Python Software Foundation
- Product
- CPython
- Classifications
- CWE-319, CWE-522, T1040
- Attack vector
- network
- Privileges
- unauthenticated
Timeline
How it unfolded
- Aug 18, 2026CVE publishedPublication date reported by the CVE source.
- Aug 21, 2026Record updatedLatest update available in the CVE record.
Exploitability
Present is not the same as exploitable
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Is a vulnerable build present?
Compare these published version ranges with your installed build and any vendor patches.
- Affected versionversion=0 <3.15.0
What conditions does exploitation require?
What is affected?
Published CVSS scores
CVSS describes severity. EPSS estimates exploitation probability.
Attacks
What attackers are doing with it
Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.
Weakness, pattern, technique
Public exploit references
- Cross-scheme Authorization header PoCproof of concept · demonstrated
Labels summarize the accepted research assessment. They do not indicate a test against your environment.
Technologies
Your stack
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Your stack
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