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Python urllib.request CVE-2026-15806

| EUVDEUVD-2026-61013 MEDIUM
Cleartext Transmission of Sensitive Information (CWE-319)
2026-08-18 PSF GHSA-2v69-2w5x-455j
Information Disclosure Cpython Suse
6.0
CVSS 4.0 · Vendor: PSF
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Severity by source

Vendor (PSF) PRIMARY
6.0 MEDIUM
CVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:P/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
vuln.today AI
5.9 MEDIUM

Network vector requires on-path position or redirect control (AC:H); no attacker privileges or victim interaction needed; only credential confidentiality is compromised.

3.1 AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N
4.0 AV:N/AC:H/AT:P/PR:N/UI:P/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N
SUSE
5.9 MEDIUM
AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N

Primary rating from Vendor (PSF).

CVSS VectorVendor: PSF

Attack Vector
Network
Attack Complexity
High
Privileges Required
None
User Interaction
P
Scope
X

Lifecycle Timeline

3
Source Code Evidence Fetched
Aug 18, 2026 - 16:54 vuln.today
Analysis Generated
Aug 18, 2026 - 16:54 vuln.today
CVE Published
Aug 18, 2026 - 15:50 cve.org
MEDIUM 6.0

DescriptionCVE.org

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.

AnalysisAI

Credential disclosure in Python's urllib.request HTTPPasswordMgr class family enables scheme-downgrade attacks that expose HTTPS-registered credentials over plaintext HTTP. Any Python application using HTTPPasswordMgr, HTTPPasswordMgrWithDefaultRealm, or HTTPPasswordMgrWithPriorAuth that stores credentials with scheme-qualified https:// URLs is affected: an attacker able to intercept traffic or inject a redirect can force the client to transmit those credentials over an unencrypted HTTP connection. …

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Vulnerability AssessmentAI

Exploitation Three concurrent conditions must be met: (1) the target Python application uses urllib.request with HTTPPasswordMgr, HTTPPasswordMgrWithDefaultRealm, or HTTPPasswordMgrWithPriorAuth, and credentials have been registered using a scheme-qualified URI such as https://example.com/ - not a bare authority like example.com or example.com:8080; (2) the application can be induced to make, or automatically follows a redirect to, a plain http:// URL on the same host for which HTTPS credentials are stored - the redirect may originate from a server response, from redirect-following logic in application code, or from attacker-controlled infrastructure; (3) the attacker can observe the resulting HTTP request, either from an on-path network position or as the entity delivering the redirect. … Additional conditions and limiting factors are described in the full assessment.
Risk Assessment The CVSS 4.0 score of 6.0 accurately reflects meaningful real-world constraints: AC:H and AT:P together require an on-path network position (or redirect injection capability) and a target application that has specifically registered credentials using scheme-qualified https:// URLs rather than bare authorities. … Full risk analysis with EPSS, KEV, and SSVC signal comparison available after sign-in.
Exploit Scenario Full exploit scenario with step-by-step reproduction available after sign-in.
Remediation The primary fix is to upgrade to the next patched CPython release once published; monitor the Python security announce list at https://mail.python.org/archives/list/security-announce@python.org/ and the advisory thread at https://mail.python.org/archives/list/security-announce@python.org/thread/3OKPE5S75KDNA7FY7AI3PL2MXM2X5RB3/ for the official release announcement, as no specific fixed version number is confirmed in the available data. … Detailed patch versions, workarounds, and compensating controls in full report.
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CVE-2026-15806 vulnerability details – vuln.today
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