urllib3 support ip address typed subject alterative names

The Fix

pip install urllib3==1.25

Based on closed urllib3/urllib3 issue #258 · 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

@@ -7,6 +7,7 @@ cache:
   - ${HOME}/.cache
 install:
+  - pip install -U setuptools
   - pip install tox==2.1.1
   - if [[ "${TOXENV}" == "gae" && ! -d ${GAE_PYTHONPATH} ]]; then

fix.md

Option A — Upgrade to fixed release\npip install urllib3==1.25\nWhen NOT to use: This fix should not be used if the application does not require IP address SAN validation.\n\n

Why This Fix Works in Production

Trigger: Could you clarify what change you're proposing? Default cert validation?
Mechanism: urllib3 fails to validate certificates with IP address SANs due to lack of support
Why the fix works: Adds support for IP address SAN fields in TLS certificates, allowing validation of certificates with IP addresses in the subject alternative name field across all Python versions. (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

Triggered by an upgrade/regression window: 3.3 breaks; 1.25 is the first fixed release.
Shows up under Python 3.3 in real deployments (not just unit tests).
urllib3 fails to validate certificates with IP address SANs due to lack of support
Production symptom (often without a traceback): Could you clarify what change you're proposing? Default cert validation?

Proof / Evidence

GitHub issue: #258
Fix PR: https://github.com/urllib3/urllib3/pull/922
First fixed release: 1.25
Affected versions: 3.3
Reproduced locally: No (not executed)
Last verified: 2026-02-09
Confidence: 0.85
Did this fix it?: Yes (upstream fix exists)
Own content ratio: 0.82

Discussion

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

Jump to Sources Open on GitHub

“That sounds sensible”

@shazow · 2013-10-10 · confirmation · source

“Could you clarify what change you're proposing? Default cert validation?”

@shazow · 2013-10-10 · source

“According to this, > The rules applied are those for checking the identity of HTTPS servers as outlined in RFC 2818, **except that IP addresses…”

@shazow · 2013-10-10 · source

“@bodgit Yes, I suspect so. Also, our pyopenssl compatibility layer requires updating. I may take a swing at this tomorrow.”

@Lukasa · 2015-12-10 · source

Failure Signature (Search String)

Could you clarify what change you're proposing? Default cert validation?
[According to this](http://docs.python.org/3.4/library/ssl.html#ssl.match_hostname),

Copy-friendly signature

signature.txt

Failure Signature
-----------------
Could you clarify what change you're proposing? Default cert validation?
[According to this](http://docs.python.org/3.4/library/ssl.html#ssl.match_hostname),

Error Message

Signature-only (no traceback captured)

error.txt

Error Message
-------------
Could you clarify what change you're proposing? Default cert validation?
[According to this](http://docs.python.org/3.4/library/ssl.html#ssl.match_hostname),

Environment

Python: 3.3

What Broke

Users experience certificate validation failures when connecting to servers via IP addresses.

Why It Broke

urllib3 fails to validate certificates with IP address SANs due to lack of support

Fix Options (Details)

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

pip install urllib3==1.25

When NOT to use: This fix should not be used if the application does not require IP address SAN validation.

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/922

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 the application does not require IP address SAN validation.

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
3.3	Broken
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 support ip address typed subject alterative names when connecting to an ip address using (Fix)