urllib3 Allow TPM/HSM private keys on the client for mTLS

The Fix

pip install urllib3==2.0.5

Based on closed urllib3/urllib3 issue #3608 · PR/commit linked

Production note: This usually shows up under retries/timeouts. Treat it as a side-effect risk until you can verify behavior with a canary + real traffic.

Open PR/Commit

@@ -0,0 +1 @@
@@ -0,0 +1 @@
+Undeprecated pyOpenSSL third-party module.
diff --git a/docs/reference/contrib/pyopenssl.rst b/docs/reference/contrib/pyopenssl.rst
index a7425b3ddf..03cda714f6 100644

fix.md

Option A — Upgrade to fixed release\npip install urllib3==2.0.5\nWhen NOT to use: This fix is not suitable if you require strict adherence to the original deprecation policy.\n\nOption C — Workaround\nseems to be to not use urllib, or generate a highly custom SSLContext in which you use e.g. OpenSSL managed keys or the tpm2-pkcs11 interface, all of which requires extensive setup, and even that might end up requiring using a lower-level library like Python http.\nWhen NOT to use: This fix is not suitable if you require strict adherence to the original deprecation policy.\n\n

Why This Fix Works in Production

Trigger: Allow TPM/HSM private keys on the client for mTLS Authentication
Mechanism: The pyOpenSSL module was deprecated, limiting support for TPM/HSM private keys
Why the fix works: Undeprecates the pyOpenSSL module, allowing for potential support of TPM/HSM private keys for mTLS authentication. (first fixed release: 2.0.5).

Production impact:

If left unfixed, the same config can fail only in production (env differences), causing startup failures or partial feature outages.

Why This Breaks in Prod

Triggered by an upgrade/regression window: 8.12.0 breaks; 2.0.5 is the first fixed release.
The pyOpenSSL module was deprecated, limiting support for TPM/HSM private keys
Production symptom (often without a traceback): Allow TPM/HSM private keys on the client for mTLS Authentication

Proof / Evidence

GitHub issue: #3608
Fix PR: https://github.com/urllib3/urllib3/pull/3127
First fixed release: 2.0.5
Affected versions: 8.12.0
Reproduced locally: No (not executed)
Last verified: 2026-02-09
Confidence: 0.95
Did this fix it?: Yes (upstream fix exists)
Own content ratio: 0.84

Discussion

High-signal excerpts from the issue thread (symptoms, repros, edge-cases).

Jump to Sources Open on GitHub

“Thanks @tsturzl! This makes sense. Thanks a lot for keeping us updated. Closing this for now, but happy to reopen if there's something urllib3 can…”

@pquentin · 2025-06-27 · confirmation · source

“Can you even share an example of configuring an SSL context today from putting to do this? Last I checked, it doesn't expose what you…”

@sigmavirus24 · 2025-05-15 · source

“https://github.com/pyca/pyopenssl/blob/62a0f5041e6a7e8c0f01b6421b4e95c6daca5f99/src/OpenSSL/crypto.py#L2343-L2351 pyOpenSSL does not support this today from what I can tell.”

@sigmavirus24 · 2025-06-20 · source

“PyOpenSSL's SSL.Context has a way to use a PKey or better yet a cryptography PrivateKey. As far as an extension goes, we're not going to…”

@sigmavirus24 · 2025-06-20 · source

Failure Signature (Search String)

Allow TPM/HSM private keys on the client for mTLS Authentication
Is it something you currently cannot do?

Copy-friendly signature

signature.txt

Failure Signature
-----------------
Allow TPM/HSM private keys on the client for mTLS Authentication
Is it something you currently cannot do?

Error Message

Signature-only (no traceback captured)

error.txt

Error Message
-------------
Allow TPM/HSM private keys on the client for mTLS Authentication
Is it something you currently cannot do?

What Broke

Clients cannot establish mTLS connections using TPM/HSM private keys, leading to authentication failures.

Why It Broke

The pyOpenSSL module was deprecated, limiting support for TPM/HSM private keys

Fix Options (Details)

Option A — Upgrade to fixed release Safe default (recommended)

pip install urllib3==2.0.5

When NOT to use: This fix is not suitable if you require strict adherence to the original deprecation policy.

Use when you can deploy the upstream fix. It is usually lower-risk than long-lived workarounds.

Option C — Workaround Temporary workaround

seems to be to not use urllib, or generate a highly custom SSLContext in which you use e.g. OpenSSL managed keys or the tpm2-pkcs11 interface, all of which requires extensive setup, and even that might end up requiring using a lower-level library like Python http.

When NOT to use: This fix is not suitable if you require strict adherence to the original deprecation policy.

Use only if you cannot change versions today. Treat this as a stopgap and remove once upgraded.

Fix reference: https://github.com/urllib3/urllib3/pull/3127

First fixed release: 2.0.5

Last verified: 2026-02-09. Validate in your environment.

When NOT to Use This Fix

This fix is not suitable if you require strict adherence to the original deprecation policy.

Did This Fix Work in Your Case?

Quick signal helps us prioritize which fixes to verify and improve.

Prevention

Add a CI check that diffs key outputs after upgrades (OpenAPI schema snapshots, JSON payload shapes, CLI output).
Upgrade behind a canary and run integration tests against the canary before 100% rollout.
Add a TLS smoke test that performs a real handshake in CI (include CA bundle validation and hostname checks).
Alert on handshake failures by error string and endpoint to catch cert/CA changes quickly.

Version Compatibility Table

Version	Status
8.12.0	Broken
2.0.5	Fixed

Related Issues

No related fixes found.

Cluster: urllib3:configuration-error urllib3 hub urllib3 best practices All hubs All clusters

Related clusters: Data consistency SSL handshake Other

Sources

We don’t republish the full GitHub discussion text. Use the links above for context.

urllib3 Allow TPM/HSM private keys on the client for mTLS Authentication (Fix)