The Fix
pip install urllib3==1.26.16
Based on closed urllib3/urllib3 issue #3035 · 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%.
@@ -1,6 +1,6 @@
MIT License
-Copyright (c) 2008-2020 Andrey Petrov and contributors (see CONTRIBUTORS.txt)
+Copyright (c) 2008-2020 Andrey Petrov and contributors.
Option A — Upgrade to fixed release\npip install urllib3==1.26.16\nWhen NOT to use: This fix should not be applied if the project requires maintaining a static list of contributors.\n\n
Why This Fix Works in Production
- Trigger: Users may be misled about contributor attribution due to outdated documentation.
- Mechanism: Removes an outdated reference to a non-existent CONTRIBUTORS.txt file in the LICENSE.txt.
- Why the fix works: Removes an outdated reference to a non-existent CONTRIBUTORS.txt file in the LICENSE.txt. (first fixed release: 1.26.16).
- 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
- Production symptom (often without a traceback): Users may be misled about contributor attribution due to outdated documentation.
Proof / Evidence
- GitHub issue: #3035
- Fix PR: https://github.com/urllib3/urllib3/pull/3039
- First fixed release: 1.26.16
- Reproduced locally: No (not executed)
- Last verified: 2026-02-09
- Confidence: 0.95
- 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).
“We've had so many contributors over the decades that it became impractical to maintain a static file in the repository, especially when Github does a…”
“@shazow Would it make sense to add that link to the LICENSE file?”
“I don't think so. Most contributors contribute under the expectation they're giving up copyright so it's not necessary to attribute copyright to the whole list.…”
“I'm in agreement that we remove the outdated reference.”
Failure Signature (Search String)
- Users may be misled about contributor attribution due to outdated documentation.
Copy-friendly signature
Failure Signature
-----------------
Users may be misled about contributor attribution due to outdated documentation.
Error Message
Signature-only (no traceback captured)
Error Message
-------------
Users may be misled about contributor attribution due to outdated documentation.
What Broke
Users may be misled about contributor attribution due to outdated documentation.
Fix Options (Details)
Option A — Upgrade to fixed release Safe default (recommended)
pip install urllib3==1.26.16
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/3039
First fixed release: 1.26.16
Last verified: 2026-02-09. Validate in your environment.
When NOT to Use This Fix
- This fix should not be applied if the project requires maintaining a static list of contributors.
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 |
|---|---|
| 1.26.16 | Fixed |
Related Issues
No related fixes found.
Sources
We don’t republish the full GitHub discussion text. Use the links above for context.