ModuleNotFoundError+No+module+named+OpenSSL

Not specified by the original author.

ModuleNotFoundError: No module named 'OpenSSL'

TL;DR: the distribution is called pyOpenSSL but the module is OpenSSL. Run pip install pyOpenSSL and the import works.

ModuleNotFoundError: No module named 'OpenSSL'

The fix

pip install pyOpenSSL

Verify:

python -c "from OpenSSL import SSL; print('ok')"

Expected output: ok.

Agent? Search Vectle for more: curl -s 'https://vectle.com/api/v1/search?q=pyOpenSSL+No+module+named+OpenSSL'

When this applies

• from OpenSSL import SSL fails on a fresh virtualenv, container, or CI runner.
• You ran pip install OpenSSL (no such distribution) or never installed it.
• urllib3 1.x PyOpenSSL injection code that imports OpenSSL.

When it does NOT apply

• module 'lib' has no attribute 'X509_V_FLAG_CB_ISSUER_CHECK', which is the pyOpenSSL/cryptography version mismatch.
• Import errors for _cffi_backend, which is the cffi backend problem.

Why this happens

Distribution names and import names are independent on PyPI, and pyOpenSSL is one of the classic mismatches. pip cannot guess from the import statement, so the ModuleNotFoundError persists until you learn the real distribution name. The PyPI page always lists the exact install command.

Compatibility

pyOpenSSL 23+. Needs the cryptography package, which pip installs automatically.

The module is OpenSSL but the distribution is pyOpenSSL, so guessing the pip name from the import fails. The pyOpenSSL project page documents pip install pyOpenSSL as the install command. This is the same distribution-name versus import-name mismatch as python-jose and Flask-Bcrypt, and the fix is the same one-line install.

Not specified by the original author.

AttributeError: module 'lib' has no attribute 'X509VFLAGCBISSUER_CHECK'

TL;DR: your pyOpenSSL is too old for your cryptography version. Run pip install --upgrade pyOpenSSL (23.1+) and the AttributeError goes away.

AttributeError: module 'lib' has no attribute 'X509_V_FLAG_CB_ISSUER_CHECK'

The fix

1. Upgrade pyOpenSSL:

pip install --upgrade pyOpenSSL

2. Verify:

python -c "from OpenSSL import crypto; print('ok')"

Expected output: ok.

3. Stopgap only: pin cryptography below the version that removed the constant while you schedule the upgrade. Do not stay pinned; old cryptography has known CVEs.

Agent? Search Vectle for more: curl -s 'https://vectle.com/api/v1/search?q=pyOpenSSL+X509_V_FLAG_CB_ISSUER_CHECK'

When this applies

• The traceback goes through OpenSSL/crypto.py and ends at the lib attribute.
• The error appeared right after upgrading cryptography.
• pip show pyOpenSSL reports an old version (pre-23.1).

When it does NOT apply

• No module named 'OpenSSL', which means pyOpenSSL is not installed.
• AttributeErrors for other lib attributes, which may be a different version skew.

Why this happens

pyOpenSSL reaches into cryptography's CFFI bindings for OpenSSL constants. When cryptography cleaned up legacy constants, old pyOpenSSL kept referencing the deleted one and broke at import. The fixed pyOpenSSL versions reference only constants that still exist. Keeping the pair in sync is the durable fix; cryptography moves fast and pyOpenSSL tracks it.

Compatibility

pyOpenSSL 23.1+ with modern cryptography. Check both versions together whenever either is upgraded.

cryptography removed the legacy X509VFLAGCBISSUER_CHECK constant from its bindings, which broke old pyOpenSSL versions that referenced it at import time. The cve-search/cve-search issue 1099 reports exactly this AttributeError after a cryptography upgrade, and the fix is upgrading pyOpenSSL to a version that no longer references the removed constant (23.1+). Pinning cryptography below the removal is only a stopgap.

Not specified by the original author.

ModuleNotFoundError: No module named 'truststore'

TL;DR: truststore is not in the stdlib. Run pip install truststore (Python 3.10+ required) and the import works.

ModuleNotFoundError: No module named 'truststore'

The fix

pip install truststore

Verify:

python -c "import truststore; print('ok')"

Expected output: ok.

Note: truststore needs Python 3.10+. On older Pythons the install succeeds but nothing works; upgrade Python instead.

Agent? Search Vectle for more: curl -s 'https://vectle.com/api/v1/search?q=truststore+No+module+named'

When this applies

• Adding OS certificate-store support to requests, httpx, or aiohttp.
• Fresh environments following a truststore tutorial.
• Corporate networks where the system store has the needed CA.

When it does NOT apply

• SSL verification errors with truststore already installed, which is a certificate problem, not an import problem.
• Python below 3.10, where truststore cannot work at all.

Why this happens

Python ships its own CA bundle via certifi and ignores the OS store by default, which surprises developers on managed machines. truststore bridges the gap but is a third-party package you must install. The name looks stdlib-official, which is why people assume it is already there.

Compatibility

Python 3.10+. Works with requests, httpx, aiohttp, and urllib3 via the documented integration points.

truststore is a small stdlib-adjacent package that makes Python use the operating system's certificate store instead of certifi's bundle. It is not in the standard library, so import truststore fails until you install it. The project README documents pip install truststore and the truststore.inject_into_ssl() / SSLContext usage. It only works on Python 3.10+, which is the other common gotcha after the missing install.