The Fix
pip install urllib3==1.26.12
Based on closed urllib3/urllib3 issue #2168 · 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%.
@@ -1,5 +1,10 @@
version: 2
+build:
+ os: ubuntu-22.04
+ tools:
Option A — Upgrade to fixed release\npip install urllib3==1.26.12\nWhen NOT to use: Do not use if it changes public behavior or if the failure cannot be reproduced.\n\nOption C — Workaround\nin just the last day or so. I was able to get RTD to build for my project by pinning urllib3 just like others here. I'm curious, for future reference, did something change on the RTD build image today or to something else to cause all this at once?\nWhen NOT to use: Do not use if it changes public behavior or if the failure cannot be reproduced.\n\n
Why This Fix Works in Production
- Trigger: Drop support for OpenSSL<1.1.1
- Mechanism: Drops support for OpenSSL versions earlier than 1.1.1, raising an ImportError for incompatible versions.
- Why the fix works: Drops support for OpenSSL versions earlier than 1.1.1, raising an ImportError for incompatible versions. (first fixed release: 1.26.12).
- 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
- Triggered by an upgrade/regression window: 1.1.1–18.04 breaks; 1.26.12 is the first fixed release.
- Shows up under Python 3.10 in real deployments (not just unit tests).
- Production symptom (often without a traceback): Drop support for OpenSSL<1.1.1
Proof / Evidence
- GitHub issue: #2168
- Fix PR: https://github.com/urllib3/urllib3/pull/2705
- First fixed release: 1.26.12
- Affected versions: 1.1.1–18.04
- Reproduced locally: No (not executed)
- Last verified: 2026-02-09
- Confidence: 0.95
- Did this fix it?: Yes (upstream fix exists)
- Own content ratio: 0.91
Discussion
High-signal excerpts from the issue thread (symptoms, repros, edge-cases).
“FYI, macOS/Xcode ships Python 3.9.6 with an ssl module compiled against LibreSSL 2.8.3. Users of this Python must now use urllib3<2 when installing urllib3. Fun…”
“Sorry to chime in negatively, but this change is causing issues all over the Web right now (ReadTheDocs.org is a good example)”
“Not at all, Gentoo stable is at 1.1.1o already.”
“It'd be interesting to see which flavors of Linux are both using OpenSSL <1.1.1 and likely to update to urllib3 v2.0 as a part of…”
Failure Signature (Search String)
- Drop support for OpenSSL<1.1.1
- Here's what OpenSSL currently supports:
Copy-friendly signature
Failure Signature
-----------------
Drop support for OpenSSL<1.1.1
Here's what OpenSSL currently supports:
Error Message
Signature-only (no traceback captured)
Error Message
-------------
Drop support for OpenSSL<1.1.1
Here's what OpenSSL currently supports:
Environment
- Python: 3.10
- urllib3: 2.0
What Broke
Users experienced build failures when using incompatible OpenSSL versions.
Fix Options (Details)
Option A — Upgrade to fixed release Safe default (recommended)
pip install urllib3==1.26.12
Use when you can deploy the upstream fix. It is usually lower-risk than long-lived workarounds.
Option C — Workaround Temporary workaround
in just the last day or so. I was able to get RTD to build for my project by pinning urllib3 just like others here. I'm curious, for future reference, did something change on the RTD build image today or to something else to cause all this at once?
Use only if you cannot change versions today. Treat this as a stopgap and remove once upgraded.
Fix reference: https://github.com/urllib3/urllib3/pull/2705
First fixed release: 1.26.12
Last verified: 2026-02-09. Validate in your environment.
When NOT to Use This Fix
- Do not use if it changes public behavior or if the failure cannot be reproduced.
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 |
|---|---|
| 1.1.1 | Broken |
| 18.04 | Broken |
| 3.10 | Broken |
| 3.7 | Broken |
| 3.9 | Broken |
| 1.26.12 | Fixed |
Related Issues
No related fixes found.
Sources
We don’t republish the full GitHub discussion text. Use the links above for context.