urllib3 SecureTransport backend can lead to long pauses on

The Fix

pip install urllib3==1.25

Based on closed urllib3/urllib3 issue #1153 · 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%.

Open PR/Commit

@@ -685,7 +685,11 @@ def makefile(self, mode, bufsize=-1):
         return _fileobject(self, mode, bufsize, close=True)
 else:  # Platform-specific: Python 3
-    makefile = backport_makefile
+    def makefile(self, mode="r", buffering=None, *args, **kwargs):
+        # We disable buffering with SecureTransport because it conflicts with

fix.md

Option A — Upgrade to fixed release\npip install urllib3==1.25\nWhen NOT to use: This fix should not be applied if using a different backend that does not exhibit this issue.\n\n

Why This Fix Works in Production

Trigger: The risk here is that there is some code somewhere in httplib that assumes it can get a `BufferedReader` unconditionally. I certainly hope that doesn't exist.
Mechanism: The SecureTransport backend's buffering conflicts with HTTPResponse's read behavior in Python 3
Why the fix works: Disables buffering when using SecureTransport to resolve long pauses on Python 3. (first fixed release: 1.25).

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

The SecureTransport backend's buffering conflicts with HTTPResponse's read behavior in Python 3
Production symptom (often without a traceback): The risk here is that there is some code somewhere in httplib that assumes it can get a `BufferedReader` unconditionally. I certainly hope that doesn't exist.

Proof / Evidence

GitHub issue: #1153
Fix PR: https://github.com/urllib3/urllib3/pull/1154
First fixed release: 1.25
Reproduced locally: No (not executed)
Last verified: 2026-02-09
Confidence: 0.85
Did this fix it?: Yes (upstream fix exists)
Own content ratio: 0.69

Discussion

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

Jump to Sources Open on GitHub

“@Lukasa I uncovered a side effect of disabling buffering while I was working on fixing #2513”

@illia-v · 2022-07-14 · source

Failure Signature (Search String)

The risk here is that there is some code somewhere in httplib that assumes it can get a `BufferedReader` unconditionally. I certainly hope that doesn't exist.
BTW, I think the bug does not concern pip because it reads only 10 KiB at a time.

Copy-friendly signature

signature.txt

Failure Signature
-----------------
The risk here is that there is some code somewhere in httplib that assumes it can get a `BufferedReader` unconditionally. I certainly hope that doesn't exist.
BTW, I think the bug does not concern pip because it reads only 10 KiB at a time.

Error Message

Signature-only (no traceback captured)

error.txt

Error Message
-------------
The risk here is that there is some code somewhere in httplib that assumes it can get a `BufferedReader` unconditionally. I certainly hope that doesn't exist.
BTW, I think the bug does not concern pip because it reads only 10 KiB at a time.

What Broke

Pip installation takes significantly longer on Python 3 compared to Python 2, causing user frustration.

Why It Broke

The SecureTransport backend's buffering conflicts with HTTPResponse's read behavior in Python 3

Fix Options (Details)

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

pip install urllib3==1.25

When NOT to use: This fix should not be applied if using a different backend that does not exhibit this issue.

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/1154

First fixed release: 1.25

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

When NOT to Use This Fix

This fix should not be applied if using a different backend that does not exhibit this issue.

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
1.25	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 SecureTransport backend can lead to long pauses on Python 3. (Fix)