urllib3 [v2] Change default TLS and ciphers to 1.2+ (Fix)

The Fix

pip install urllib3==1.26.3

Based on closed urllib3/urllib3 issue #1989 · 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

@@ -482,36 +482,3 @@ class SecurityConst:
     errSecItemNotFound = -25300
     errSecInvalidTrustSettings = -25262
-
-    # Cipher suites. We only pick the ones our default cipher string allows.
-    # Source: https://developer.apple.com/documentation/security/1550981-ssl_cipher_suite_values

fix.md

Option A — Upgrade to fixed release\npip install urllib3==1.26.3\nWhen NOT to use: This fix should not be used if maintaining legacy support for older TLS versions is required.\n\n

Why This Fix Works in Production

Trigger: [v2] Change default TLS and ciphers to 1.2+
Mechanism: Modifies the default TLS and cipher settings to use system-configured ciphers for OpenSSL 1.1.1 and above, addressing issue #1989.
Why the fix works: Modifies the default TLS and cipher settings to use system-configured ciphers for OpenSSL 1.1.1 and above, addressing issue #1989. (first fixed release: 1.26.3).

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

Triggered by an upgrade/regression window: 1.0–1.2 breaks; 1.26.3 is the first fixed release.
Production symptom (often without a traceback): [v2] Change default TLS and ciphers to 1.2+

Proof / Evidence

GitHub issue: #1989
Fix PR: https://github.com/urllib3/urllib3/pull/2082
First fixed release: 1.26.3
Affected versions: 1.0–1.2
Reproduced locally: No (not executed)
Last verified: 2026-02-09
Confidence: 0.95
Did this fix it?: Yes (upstream fix exists)
Own content ratio: 0.72

Discussion

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

Jump to Sources Open on GitHub

“Two questions: * Is TLS 1.0+ the minimum supported version for v2? * Is this why we have to default to 1.0+ when given ciphers?…”

@pquentin · 2020-12-16 · source

“- We haven't discussed minimum protocol version, I'm not sure we need to take a stance on this as the problem will likely resolve itself…”

@sethmlarson · 2020-12-16 · source

Failure Signature (Search String)

[v2] Change default TLS and ciphers to 1.2+
- If we're given no `ssl_context`, `ssl_version`, or `ssl_ciphers` we should be using TLS 1.2+ and a much tighter cipher list.

Copy-friendly signature

signature.txt

Failure Signature
-----------------
[v2] Change default TLS and ciphers to 1.2+
- If we're given no `ssl_context`, `ssl_version`, or `ssl_ciphers` we should be using TLS 1.2+ and a much tighter cipher list.

Error Message

Signature-only (no traceback captured)

error.txt

Error Message
-------------
[v2] Change default TLS and ciphers to 1.2+
- If we're given no `ssl_context`, `ssl_version`, or `ssl_ciphers` we should be using TLS 1.2+ and a much tighter cipher list.

What Broke

Insecure TLS versions and ciphers could lead to security vulnerabilities in production environments.

Fix Options (Details)

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

pip install urllib3==1.26.3

When NOT to use: This fix should not be used if maintaining legacy support for older TLS versions is required.

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/2082

First fixed release: 1.26.3

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

When NOT to Use This Fix

This fix should not be used if maintaining legacy support for older TLS versions is 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.
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
1.0	Broken
1.2	Broken
1.26.3	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.