The Fix
pip install urllib3==1.25
Based on closed urllib3/urllib3 issue #579 · 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%.
@@ -229,6 +229,11 @@ def test_absolute_url(self):
c._absolute_url('path?query=foo'))
+ def test_ca_certs_default_cert_required(self):
+ with connection_from_url('https://google.com:80', ca_certs='/etc/ssl/certs/custom.pem') as pool:
+ conn = pool._get_conn()
Option A — Upgrade to fixed release\npip install urllib3==1.25\nWhen NOT to use: This fix should not be used if custom cert_reqs values are required.\n\n
Why This Fix Works in Production
- Trigger: Is this a reasonable change? Would make our boilerplate a little simpler/less crufty.
- Mechanism: The default value for cert_reqs was not set when ca_certs was provided
- Why the fix works: Set cert_reqs to 'CERT_REQUIRED' by default if ca_certs is passed. (first fixed release: 1.25).
- 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 default value for cert_reqs was not set when ca_certs was provided
- Production symptom (often without a traceback): Is this a reasonable change? Would make our boilerplate a little simpler/less crufty.
Proof / Evidence
- GitHub issue: #579
- Fix PR: https://github.com/urllib3/urllib3/pull/650
- 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).
“@Lukasa @sigmavirus24 @dstufft Thoughts on this?”
“Consider me :+1: That said, we should allow people to use alternate values if they know they need it.”
“Yea, it would be merely a default. Override would work as before.”
Failure Signature (Search String)
- Is this a reasonable change? Would make our boilerplate a little simpler/less crufty.
Copy-friendly signature
Failure Signature
-----------------
Is this a reasonable change? Would make our boilerplate a little simpler/less crufty.
Error Message
Signature-only (no traceback captured)
Error Message
-------------
Is this a reasonable change? Would make our boilerplate a little simpler/less crufty.
What Broke
Users may experience SSL connection issues due to missing cert_reqs configuration.
Why It Broke
The default value for cert_reqs was not set when ca_certs was provided
Fix Options (Details)
Option A — Upgrade to fixed release Safe default (recommended)
pip install urllib3==1.25
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/650
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 used if custom cert_reqs values are required.
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.
Version Compatibility Table
| Version | Status |
|---|---|
| 1.25 | Fixed |
Related Issues
No related fixes found.
Sources
We don’t republish the full GitHub discussion text. Use the links above for context.