urllib3 Find out why the SSLKEYLOGFILE fails on AppVeyor

The Fix

pip install urllib3==1.25.9

Based on closed urllib3/urllib3 issue #1889 · 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

@@ -698,16 +698,10 @@ def test_tls_protocol_name_of_socket(self):
                 conn.close()
 
-    @pytest.mark.skipif(
-        not hasattr(ssl.SSLContext, "keylog_filename"),
-        reason="requires OpenSSL 1.1.1+",

fix.md

Option A — Upgrade to fixed release\npip install urllib3==1.25.9\nWhen NOT to use: Do not use this fix if the OpenSSL version does not support keylog_filename.\n\n

Why This Fix Works in Production

Trigger: Find out why the SSLKEYLOGFILE fails on AppVeyor
Mechanism: The test for SSLKEYLOGFILE failed on AppVeyor due to OpenSSL support issues
Why the fix works: Fixes the SSLKEYLOGFILE issue on AppVeyor by adjusting the test conditions based on OpenSSL support. (first fixed release: 1.25.9).

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 test for SSLKEYLOGFILE failed on AppVeyor due to OpenSSL support issues
Production symptom (often without a traceback): Find out why the SSLKEYLOGFILE fails on AppVeyor

Proof / Evidence

GitHub issue: #1889
Fix PR: https://github.com/urllib3/urllib3/pull/1893
First fixed release: 1.25.9
Reproduced locally: No (not executed)
Last verified: 2026-02-09
Confidence: 0.85
Did this fix it?: Yes (upstream fix exists)
Own content ratio: 0.71

Discussion

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

Jump to Sources Open on GitHub

“See https://github.com/urllib3/urllib3/pull/1867 for details. @bastiaanb mentions that the feature works on Windows, but the test fails on AppVeyor, so we had to skip the test on Windows.”

Issue thread · issue description · source

Failure Signature (Search String)

Find out why the SSLKEYLOGFILE fails on AppVeyor
See https://github.com/urllib3/urllib3/pull/1867 for details. @bastiaanb mentions that the feature works on Windows, but the test fails on AppVeyor, so we had to skip the test on

Copy-friendly signature

signature.txt

Failure Signature
-----------------
Find out why the SSLKEYLOGFILE fails on AppVeyor
See https://github.com/urllib3/urllib3/pull/1867 for details. @bastiaanb mentions that the feature works on Windows, but the test fails on AppVeyor, so we had to skip the test on Windows.

Error Message

Signature-only (no traceback captured)

error.txt

Error Message
-------------
Find out why the SSLKEYLOGFILE fails on AppVeyor
See https://github.com/urllib3/urllib3/pull/1867 for details. @bastiaanb mentions that the feature works on Windows, but the test fails on AppVeyor, so we had to skip the test on Windows.

What Broke

Tests for SSLKEYLOGFILE were skipped on Windows, leading to potential undetected failures.

Why It Broke

The test for SSLKEYLOGFILE failed on AppVeyor due to OpenSSL support issues

Fix Options (Details)

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

pip install urllib3==1.25.9

When NOT to use: Do not use this fix if the OpenSSL version does not support keylog_filename.

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/1893

First fixed release: 1.25.9

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

When NOT to Use This Fix

Do not use this fix if the OpenSSL version does not support keylog_filename.

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
1.25.9	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 Find out why the SSLKEYLOGFILE fails on AppVeyor (Fix)