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A malformed certificate in the Windows certificate store can prevent Python’s OpenSSL-backed SSL context from loading certificates and disrupt applications that use that path. It does not mean every Python tool is affected, and the error alone does not prove that a remote website has a bad certificate. Start by checking whether a minimal Python SSL context reproduces the failure; avoid deleting certificates or turning off verification as a first response.
What “[ASN1] nested asn1 error” means in this Windows scenario
Python’s ssl module uses OpenSSL. When an application creates a default SSL context without supplying explicit CA inputs, Python can load the system’s default CA certificates. On Windows, certificate enumeration exposes certificate data that OpenSSL must parse. If parsing fails on malformed certificate data, the context may fail during certificate loading, before or as the application prepares a TLS connection. Python’s SSL documentation describes the module, default context behavior, and Windows certificate enumeration.
That makes this a local certificate-loading problem in the documented failure mode—not proof that the remote server’s certificate is invalid. The exact error text can vary with the Python and OpenSSL versions, so record the full traceback rather than relying on the suffix alone.
Why “every Python tool” is too broad
CPython issue 104135, opened May 3, 2023, reports Windows Python raising ASN.1-related SSL errors while loading certificates from the system store. Its author described the behavior this way: “It is loading all root certs from the Windows certificate store at once, and it fails if it encounters a single malformed certificate instead of ignoring it and not adding it to its own trust store.” That is the issue author’s description, not an accepted CPython finding or fix. The issue is closed as “not planned.” CPython issue 104135
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Only programs whose execution path creates an SSL context that loads the affected store are exposed to this particular failure. Applications that use a different TLS stack, supply an explicit CA configuration, or do not use TLS may behave differently. The available reports do not establish the behavior of every current Python package, distribution, or application.
Check whether Python’s default SSL context reproduces the failure
Capture enough detail to distinguish a certificate-store loading failure from an application-specific TLS problem:
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- Save the complete traceback, including the exact error string.
- Record the Python version and distribution, and whether Python is running in a virtual environment or another managed environment.
- Run a minimal test with the same Python executable and environment as the affected application.
python -c "import ssl; ssl.create_default_context(); print('Default SSL context created')"If the command raises the same ASN.1-related ssl.SSLError, that supports the diagnosis that default-context certificate loading is failing in that environment. If it succeeds, the original application may use a different SSL setup or fail later for another reason; compare its configuration and traceback rather than assuming the store is at fault.
Choose a safe remediation path
Ask an administrator to inspect the Windows certificate store
If the minimal test reproduces the error, share the traceback, Python version, and environment details with the system or certificate-store administrator. Ask them to identify the problematic entry and assess it before making a change. You may not have the permissions needed to inspect or modify the store, and deleting a certificate without understanding its role can disrupt trust for other software. CPython issue 104135 specifically cautions against randomly removing certificates.
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Use an approved CA bundle only when the application supports it
Python’s SSL APIs allow explicit CA certificate inputs. If the application can be configured to use an organization-approved CA bundle, that may avoid loading the problematic system-store path. Preserve certificate verification, and have the bundle and configuration approved for the environment. An arbitrary or unverified trust bundle is not a safe substitute for diagnosing the store problem. See the Python SSL documentation for the relevant context and CA-loading behavior.
Check the specific Python distribution or application for a downstream change
The CPython issue is closed as “not planned.” Its body suggests processing certificates individually and ignoring parse failures, but that suggestion is not an accepted CPython remedy or a guaranteed workaround. Check the release notes or support guidance for the exact Python distribution or application you use before assuming its behavior has changed.
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What the historical Windows report does—and does not—show
A separate Python tracker report documented Windows 10 with Python 3.7.1 and 3.7.2 raising ssl.SSLError: nested asn1 error from ssl.create_default_context(). On January 7, 2019, Python core developer Victor Stinner commented, “It seems like one of your certificate is invalid.” His analysis concerned that report’s reproduction; it does not establish that all present-day Windows certificate stores contain the same problem. Historical Python tracker report
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Actions that can make the problem worse
- Do not disable certificate verification. Setting verification to
CERT_NONEremoves an important TLS security check; it does not repair the certificate-loading failure safely. - Do not delete root certificates blindly. A certificate may be required by Windows or other applications, and removing it can break their trust relationships.
- Do not install an unverified CA bundle. Use only a bundle approved for your environment, with certificate verification still enabled.
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