urllib3 TLS 1.3 Post Handshake Auth no longer working with

The Fix

pip install urllib3==2.2.0

Based on closed urllib3/urllib3 issue #3325 · PR/commit linked

Production note: Most teams hit this during upgrades or environment changes. Roll out with a canary and smoke critical endpoints (health, OpenAPI/docs) before 100%.

Jump to Verify Open PR/Commit

@@ -0,0 +1 @@
@@ -0,0 +1 @@
+Fixed TLS 1.3 Post Handshake Auth when the server certificate validation was disabled.
diff --git a/src/urllib3/util/ssl_.py b/src/urllib3/util/ssl_.py
index e0a7c04a3c..b14cf27b61 100644

repro.py

import platform
import ssl
import urllib3

print("OS", platform.platform())
print("Python", platform.python_version())
print(ssl.OPENSSL_VERSION)
print("urllib3", urllib3.__version__)

verify

Re-run the minimal reproduction on your broken version, then apply the fix and re-run.

fix.md

Option A — Upgrade to fixed release\npip install urllib3==2.2.0\nWhen NOT to use: Do not use this fix if server certificate validation is required.\n\n

Why This Fix Works in Production

Trigger: TLS 1.3 Post Handshake Auth no longer working with urllib 2.1.0 when ignoring cert validation
Mechanism: The change in the commit restricted post_handshake_auth to only when cert_reqs is CERT_REQUIRED
Why the fix works: Fixed TLS 1.3 Post Handshake Auth when the server certificate validation was disabled. (first fixed release: 2.2.0).

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

Shows up under Python 3.7 in real deployments (not just unit tests).
The change in the commit restricted post_handshake_auth to only when cert_reqs is CERT_REQUIRED
Production symptom (often without a traceback): TLS 1.3 Post Handshake Auth no longer working with urllib 2.1.0 when ignoring cert validation

Proof / Evidence

GitHub issue: #3325
Fix PR: https://github.com/urllib3/urllib3/pull/3326
First fixed release: 2.2.0
Reproduced locally: No (not executed)
Last verified: 2026-02-09
Confidence: 0.75
Did this fix it?: Yes (upstream fix exists)
Own content ratio: 0.70

Discussion

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

Jump to Sources Open on GitHub

“Thank you for reporting this issue and opening a fix!”

@sethmlarson · 2024-01-29 · source

Failure Signature (Search String)

TLS 1.3 Post Handshake Auth no longer working with urllib 2.1.0 when ignoring cert validation
if (cert_reqs == ssl.CERT_REQUIRED or sys.version_info >= (3, 7, 4)) and getattr(

Copy-friendly signature

signature.txt

Failure Signature
-----------------
TLS 1.3 Post Handshake Auth no longer working with urllib 2.1.0 when ignoring cert validation
if (cert_reqs == ssl.CERT_REQUIRED or sys.version_info >= (3, 7, 4)) and getattr(

Error Message

Signature-only (no traceback captured)

error.txt

Error Message
-------------
TLS 1.3 Post Handshake Auth no longer working with urllib 2.1.0 when ignoring cert validation
if (cert_reqs == ssl.CERT_REQUIRED or sys.version_info >= (3, 7, 4)) and getattr(

Minimal Reproduction

repro.py

import platform
import ssl
import urllib3

print("OS", platform.platform())
print("Python", platform.python_version())
print(ssl.OPENSSL_VERSION)
print("urllib3", urllib3.__version__)

Environment

Python: 3.7
urllib3: 2.1.0

What Broke

Authentication fails and the TLS socket is closed by the server due to missing client certificate.

Why It Broke

The change in the commit restricted post_handshake_auth to only when cert_reqs is CERT_REQUIRED

Fix Options (Details)

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

pip install urllib3==2.2.0

When NOT to use: Do not use this fix if server certificate validation is required.

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

Fix reference: https://github.com/urllib3/urllib3/pull/3326

First fixed release: 2.2.0

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

When NOT to Use This Fix

Do not use this fix if server certificate validation is required.

Verify Fix

verify

Re-run the minimal reproduction on your broken version, then apply the fix and re-run.

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
2.2.0	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 TLS 1.3 Post Handshake Auth no longer working with urllib 2.1.0 when ignoring cert (Fix)