urllib3 Remove TLS13-* suites from DEFAULT

The Fix

pip install urllib3==1.25

Based on closed urllib3/urllib3 issue #1386 · 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

@@ -22,6 +22,14 @@ dev (master)
   ``urllib3[brotli]`` extra. (Pull #1532)
 
+* Add TLSv1.3 support to CPython, pyOpenSSL, and SecureTransport ``SSLContext``
+  implementations. (Pull #1496)
+

fix.md

Option A — Upgrade to fixed release\npip install urllib3==1.25\nWhen NOT to use: Do not apply this fix if using an older version of OpenSSL that does not support TLS 1.3.\n\n

Why This Fix Works in Production

Trigger: Remove TLS13-* suites from DEFAULT_CIPHERS
Mechanism: Adds support for TLS 1.3 to all HTTPSConnection implementations and removes TLS 1.3 cipher suites from DEFAULT_CIPHERS.
Why the fix works: Adds support for TLS 1.3 to all HTTPSConnection implementations and removes TLS 1.3 cipher suites from DEFAULT_CIPHERS. (first fixed release: 1.25).

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

Production symptom (often without a traceback): Remove TLS13-* suites from DEFAULT_CIPHERS

Proof / Evidence

GitHub issue: #1386
Fix PR: https://github.com/urllib3/urllib3/pull/1496
First fixed release: 1.25
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).

Jump to Sources Open on GitHub

“Should we defer removing the TLS 1.3 cipher suites until the SSL_CTX_set_ciphersuites() feature is exposed in PyOpenSSL or CPython? Would love your recommendation on how…”

@sethmlarson · 2018-05-21 · source

Failure Signature (Search String)

Remove TLS13-* suites from DEFAULT_CIPHERS
https://github.com/openssl/openssl/pull/5392

Copy-friendly signature

signature.txt

Failure Signature
-----------------
Remove TLS13-* suites from DEFAULT_CIPHERS
https://github.com/openssl/openssl/pull/5392

Error Message

Signature-only (no traceback captured)

error.txt

Error Message
-------------
Remove TLS13-* suites from DEFAULT_CIPHERS
https://github.com/openssl/openssl/pull/5392

Fix Options (Details)

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

pip install urllib3==1.25

When NOT to use: Do not apply this fix if using an older version of OpenSSL that does not support TLS 1.3.

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/1496

First fixed release: 1.25

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

When NOT to Use This Fix

Do not apply this fix if using an older version of OpenSSL that does not support TLS 1.3.

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	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 Remove TLS13-* suites from DEFAULT_CIPHERS (Fix)