urllib3 Potential regression in 2.0.0 (commit

The Fix

pip install urllib3==2.0.1

Based on closed urllib3/urllib3 issue #2999 · PR/commit linked

Open PR/Commit

@@ -0,0 +1 @@
@@ -0,0 +1 @@
+avoid a ``ResourceWarning`` if ``assert_fingerprint`` or ``match_hostname`` fail
diff --git a/src/urllib3/connection.py b/src/urllib3/connection.py
index 1f13af0b63..9dc04fe099 100644

fix.md

Option A — Upgrade to fixed release\npip install urllib3==2.0.1\nWhen NOT to use: Do not apply this fix if the application relies on the previous behavior of not closing sockets.\n\n

Why This Fix Works in Production

Trigger: Potential regression in 2.0.0 (commit ea96fde9450b2d0d233f0414c7be0a75148fae8b)
Mechanism: The SSLSocket was not closed properly when fingerprint verification failed, causing tests to hang
Why the fix works: Ensures that the SSLSocket is closed if the assert_fingerprint or match_hostname fails, addressing the hanging issue in tests. (first fixed release: 2.0.1).

Why This Breaks in Prod

The SSLSocket was not closed properly when fingerprint verification failed, causing tests to hang
Production symptom (often without a traceback): Potential regression in 2.0.0 (commit ea96fde9450b2d0d233f0414c7be0a75148fae8b)

Proof / Evidence

GitHub issue: #2999
Fix PR: https://github.com/urllib3/urllib3/pull/2992
First fixed release: 2.0.1
Reproduced locally: No (not executed)
Last verified: 2026-02-09
Confidence: 0.75
Did this fix it?: Yes (upstream fix exists)
Own content ratio: 0.77

Discussion

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

Jump to Sources Open on GitHub

“This is fixed by https://github.com/urllib3/urllib3/pull/2992”

@graingert · 2023-04-29 · confirmation · source

“I was able to reproduce the hang wihout apm-agent-python: https://gist.github.com/pquentin/dddb538fe71d6a2b31e57918cda74047. Just run pytest -v, the second test will hang with urllib3 2.0.”

@pquentin · 2023-04-29 · source

“So we have tests in urllib3 that do exactly that: test_verify_none_and_good_fingerprint and test_verify_none_and_bad_fingerprint”

@pquentin · 2023-04-29 · source

Failure Signature (Search String)

Potential regression in 2.0.0 (commit ea96fde9450b2d0d233f0414c7be0a75148fae8b)
Previously the test `test_ssl_cert_pinning_fails` would succeed in 1.26.15, but fails by hanging in 2.0.0:

Copy-friendly signature

signature.txt

Failure Signature
-----------------
Potential regression in 2.0.0 (commit ea96fde9450b2d0d233f0414c7be0a75148fae8b)
Previously the test `test_ssl_cert_pinning_fails` would succeed in 1.26.15, but fails by hanging in 2.0.0:

Error Message

Signature-only (no traceback captured)

error.txt

Error Message
-------------
Potential regression in 2.0.0 (commit ea96fde9450b2d0d233f0414c7be0a75148fae8b)
Previously the test `test_ssl_cert_pinning_fails` would succeed in 1.26.15, but fails by hanging in 2.0.0:

Environment

urllib3: 2.0

What Broke

Tests hang indefinitely during SSL certificate verification, impacting CI/CD pipelines.

Why It Broke

The SSLSocket was not closed properly when fingerprint verification failed, causing tests to hang

Fix Options (Details)

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

pip install urllib3==2.0.1

When NOT to use: Do not apply this fix if the application relies on the previous behavior of not closing sockets.

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/2992

First fixed release: 2.0.1

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

When NOT to Use This Fix

Do not apply this fix if the application relies on the previous behavior of not closing sockets.

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
2.0.1	Fixed

Related Issues

No related fixes found.

Cluster: urllib3:ssl-handshake urllib3 hub urllib3 best practices All hubs All clusters

Related clusters: Configuration error Data consistency Other

Sources

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

urllib3 Potential regression in 2.0.0 (commit ea96fde9450b2d0d233f0414c7be0a75148fae8b) (Fix)