The Fix
pip install urllib3==1.25
Based on closed urllib3/urllib3 issue #1316 · 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%.
@@ -4,6 +4,10 @@ Changes
------------
+* Allow providing a list of headers to strip from requests when redirecting
+ to a different host. Defaults to the ``Authorization`` header. Different
+ headers can be set via ``Retry.remove_headers_on_redirect``. (Issue #1316)
Option A — Upgrade to fixed release\npip install urllib3==1.25\nWhen NOT to use: This fix should not be used if the application requires forwarding authentication headers across hosts.\n\nOption C — Workaround\nfor now is to use a monkey patch to remove auth.\nWhen NOT to use: This fix should not be used if the application requires forwarding authentication headers across hosts.\n\n
Why This Fix Works in Production
- Trigger: Except urllib3 doesn't directly handle authentication the way Requests does. I don't disagree, but there are fundamentally different layers of concern here.
- Mechanism: The Authorization header was not removed during redirects to different hosts
- Why the fix works: This change removes the Authorization header when redirecting to a different host, addressing issue #1316. (first fixed release: 1.25).
- 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
- The Authorization header was not removed during redirects to different hosts
- Production symptom (often without a traceback): Except urllib3 doesn't directly handle authentication the way Requests does. I don't disagree, but there are fundamentally different layers of concern here.
Proof / Evidence
- GitHub issue: #1316
- Fix PR: https://github.com/urllib3/urllib3/pull/1346
- 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: 0.68
Discussion
High-signal excerpts from the issue thread (symptoms, repros, edge-cases).
“Btw if we decide it's a good idea and nobody wants to do it, I'll put together a quick PR. Should be 4-5 lines of…”
“Except urllib3 doesn't directly handle authentication the way Requests does. I don't disagree, but there are fundamentally different layers of concern here.”
“@haikuginger actually, cURL preserves authentication on redirect in the face of leaking credential”
“I agree this is a potential footgun. I'd almost be tempted to turn off redirect following by default.”
Failure Signature (Search String)
- Except urllib3 doesn't directly handle authentication the way Requests does. I don't disagree, but there are fundamentally different layers of concern here.
- urllib3 redirects across hosts by default these days, doesn't it? Sounds like a pretty scary surprise-footgun to have.
Copy-friendly signature
Failure Signature
-----------------
Except urllib3 doesn't directly handle authentication the way Requests does. I don't disagree, but there are fundamentally different layers of concern here.
urllib3 redirects across hosts by default these days, doesn't it? Sounds like a pretty scary surprise-footgun to have.
Error Message
Signature-only (no traceback captured)
Error Message
-------------
Except urllib3 doesn't directly handle authentication the way Requests does. I don't disagree, but there are fundamentally different layers of concern here.
urllib3 redirects across hosts by default these days, doesn't it? Sounds like a pretty scary surprise-footgun to have.
What Broke
Users experienced credential leaks when redirecting to different hosts with authentication headers.
Why It Broke
The Authorization header was not removed during redirects to different hosts
Fix Options (Details)
Option A — Upgrade to fixed release Safe default (recommended)
pip install urllib3==1.25
Use when you can deploy the upstream fix. It is usually lower-risk than long-lived workarounds.
Option C — Workaround Temporary workaround
for now is to use a monkey patch to remove auth.
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/1346
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 requires forwarding authentication headers across hosts.
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 |
|---|---|
| 1.25 | Fixed |
Related Issues
No related fixes found.
Sources
We don’t republish the full GitHub discussion text. Use the links above for context.