urllib3 SSLV3_ALERT_HANDSHAKE_FAILURE after upgrading to

The Fix

pip install urllib3==1.25.2

Based on closed urllib3/urllib3 issue #1582 · 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%.

Jump to Verify Open PR/Commit

@@ -1,6 +1,12 @@
 =======
 
+dev (master)
+------------
+

repro.py

Traceback (most recent call last):
  File "/home/travis/build/h3llrais3r/Auto-Subliminal/lib/urllib3/connectionpool.py", line 603, in urlopen
    chunked=chunked)
  File "/home/travis/build/h3llrais3r/Auto-Subliminal/lib/urllib3/connectionpool.py", line 344, in _make_request
    self._validate_conn(conn)
  File "/home/travis/build/h3llrais3r/Auto-Subliminal/lib/urllib3/connectionpool.py", line 843, in _validate_conn
    conn.connect()
  File "/home/travis/build/h3llrais3r/Auto-Subliminal/lib/urllib3/connection.py", line 350, in connect
    ssl_context=context)
  File "/home/travis/build/h3llrais3r/Auto-Subliminal/lib/urllib3/util/ssl_.py", line 369, in ssl_wrap_socket
    return context.wrap_socket(sock)
  File "/opt/python/3.6.3/lib/python3.6/ssl.py", line 407, in wrap_socket
    _context=self, _session=session)
  File "/opt/python/3.6.3/lib/python3.6/ssl.py", line 814, in __init__
    self.do_handshake()
  File "/opt/python/3.6.3/lib/python3.6/ssl.py", line 1068, in do_handshake
    self._sslobj.do_handshake()
  File "/opt/python/3.6.3/lib/python3.6/ssl.py", line 689, in do_handshake
    self._sslobj.do_handshake()
ssl.SSLError: [SSL: SSLV3_ALERT_HANDSHAKE_FAILURE] sslv3 alert handshake failure (_ssl.c:777)
During handling of the above exception, another exception occurred:
Traceback (most recent call last):
  File "/home/travis/build/h3llrais3r/Auto-Subliminal/lib/requests/adapters.py", line 449, in send
    timeout=timeout
  File "/home/travis/build/h3llrais3r/Auto-Subliminal/lib/urllib3/connectionpool.py", line 641, in urlopen
    _stacktrace=sys.exc_info()[2])
  File "/home/travis/build/h3llrais3r/Auto-Subliminal/lib/urllib3/util/retry.py", line 399, in increment
    raise MaxRetryError(_pool, url, error or ResponseError(cause))
urllib3.exceptions.MaxRetryError: HTTPSConnectionPool(host='v2.sg.media-imdb.com', port=443): Max retries exceeded with url: /suggests/s/Southpaw.json (Caused by SSLError(SSLError(1, '[SSL: SSLV3_ALERT_HANDSHAKE_FAILURE] sslv3 alert handshake failure (_ssl.c:777)'),))
During handling of the above exception, another exception occurred:
Traceback (most recent call last):
  File "/home/travis/build/h3llrais3r/Auto-Subliminal/autosubliminal/indexer.py", line 351, in get_imdb_id_and_year
    api_obj = self._search(title, year)
  File "/home/travis/build/h3llrais3r/Auto-Subliminal/autosubliminal/indexer.py", line 273, in _search
    search_results = ImdbFacade().search_for_title(title)
  File "/home/travis/build/h3llrais3r/Auto-Subliminal/lib/imdbpie/facade.py", line 87, in search_for_title
    for result in self._client.search_for_title(query):
  File "/home/travis/build/h3llrais3r/Auto-Subliminal/lib/imdbpie/imdbpie.py", line 182, in search_for_title
    search_results = self._suggest_search(title)
  File "/home/travis/build/h3llrais3r/Auto-Subliminal/lib/imdbpie/imdbpie.py", line 160, in _suggest_search
    search_results = self._get(url=url, query=query_encoded)
  File "/home/travis/build/h3llrais3r/Auto-Subliminal/lib/imdbpie/imdbpie.py", line 308, in _get
    resp = self.session.get(url, headers=headers, params=params)
  File "/home/travis/build/h3llrais3r/Auto-Subliminal/lib/requests/sessions.py", line 546, in get
    return self.request('GET', url, **kwargs)
  File "/home/travis/build/h3llrais3r/Auto-Subliminal/lib/requests/sessions.py", line 533, in request
    resp = self.send(prep, **send_kwargs)
  File "/home/travis/build/h3llrais3r/Auto-Subliminal/lib/requests/sessions.py", line 646, in send
    r = adapter.send(request, **kwargs)
  File "/home/travis/build/h3llrais3r/Auto-Subliminal/lib/requests/
... (truncated) ...

verify

Re-run the minimal reproduction on your broken version, then apply the fix and re-run.

fix.md

Option A — Upgrade to fixed release\npip install urllib3==1.25.2\nWhen NOT to use: This fix should not be applied if the application requires support for IPvFuture addresses.\n\n

Why This Fix Works in Production

Trigger: chunked=chunked)
Mechanism: The SSL handshake failure occurs due to incorrect detection of IPvFuture addresses
Why the fix works: Addresses an SSL handshake failure by modifying the detection of IP addresses to exclude IPvFuture addresses, resolving issue #1582. (first fixed release: 1.25.2).

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

Shows up under Python 3.6 in real deployments (not just unit tests).
The SSL handshake failure occurs due to incorrect detection of IPvFuture addresses
Surfaces as: Traceback (most recent call last):

Proof / Evidence

GitHub issue: #1582
Fix PR: https://github.com/urllib3/urllib3/pull/1583
First fixed release: 1.25.2
Reproduced locally: No (not executed)
Last verified: 2026-02-09
Confidence: 0.95
Did this fix it?: Yes (upstream fix exists)
Own content ratio: 0.32

Discussion

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

Jump to Sources Open on GitHub

“Are you providing a proper CA cert for that ConnectionPool? One of the changes in 1.25 is that cert_reqs defaults to CERT_REQUIRED.”

@sethmlarson · 2019-04-24 · source

“I'm not using a CA cert”

@h3llrais3r · 2019-04-24 · source

“Thanks for investigation. Let me know if I need to test something. :wink:”

@h3llrais3r · 2019-04-24 · source

“Thanks. Latest release solved the issue. :+1:”

@h3llrais3r · 2019-04-29 · source

Failure Signature (Search String)

chunked=chunked)

Error Message

Stack trace

error.txt

Error Message
-------------
Traceback (most recent call last):
  File "/home/travis/build/h3llrais3r/Auto-Subliminal/lib/urllib3/connectionpool.py", line 603, in urlopen
    chunked=chunked)
  File "/home/travis/build/h3llrais3r/Auto-Subliminal/lib/urllib3/connectionpool.py", line 344, in _make_request
    self._validate_conn(conn)
  File "/home/travis/build/h3llrais3r/Auto-Subliminal/lib/urllib3/connectionpool.py", line 843, in _validate_conn
    conn.connect()
  File "/home/travis/build/h3llrais3r/Auto-Subliminal/lib/urllib3/connection.py", line 350, in connect
    ssl_context=context)
  File "/home/travis/build/h3llrais3r/Auto-Subliminal/lib/urllib3/util/ssl_.py", line 369, in ssl_wrap_socket
    return context.wrap_socket(sock)
  File "/opt/python/3.6.3/lib/python3.6/ssl.py", line 407, in wrap_socket
    _context=self, _session=session)
  File "/opt/python/3.6.3/lib/python3.6/ssl.py", line 814, in __init__
    self.do_handshake()
  File "/opt/python/3.6.3/lib/python3.6/ssl.py", line 1068, in do_handshake
    self._sslobj.do_handshake()
  File "/opt/python/3.6.3/lib/python3.6/ssl.py", line 689, in do_handshake
    self._sslobj.do_handshake()
ssl.SSLError: [SSL: SSLV3_ALERT_HANDSHAKE_FAILURE] sslv3 alert handshake failure (_ssl.c:777)
During handling of the above exception, another exception occurred:
Traceback (most recent call last):
  File "/home/travis/build/h3llrais3r/Auto-Subliminal/lib/requests/a
... (truncated) ...

Minimal Reproduction

repro.py

Traceback (most recent call last):
  File "/home/travis/build/h3llrais3r/Auto-Subliminal/lib/urllib3/connectionpool.py", line 603, in urlopen
    chunked=chunked)
  File "/home/travis/build/h3llrais3r/Auto-Subliminal/lib/urllib3/connectionpool.py", line 344, in _make_request
    self._validate_conn(conn)
  File "/home/travis/build/h3llrais3r/Auto-Subliminal/lib/urllib3/connectionpool.py", line 843, in _validate_conn
    conn.connect()
  File "/home/travis/build/h3llrais3r/Auto-Subliminal/lib/urllib3/connection.py", line 350, in connect
    ssl_context=context)
  File "/home/travis/build/h3llrais3r/Auto-Subliminal/lib/urllib3/util/ssl_.py", line 369, in ssl_wrap_socket
    return context.wrap_socket(sock)
  File "/opt/python/3.6.3/lib/python3.6/ssl.py", line 407, in wrap_socket
    _context=self, _session=session)
  File "/opt/python/3.6.3/lib/python3.6/ssl.py", line 814, in __init__
    self.do_handshake()
  File "/opt/python/3.6.3/lib/python3.6/ssl.py", line 1068, in do_handshake
    self._sslobj.do_handshake()
  File "/opt/python/3.6.3/lib/python3.6/ssl.py", line 689, in do_handshake
    self._sslobj.do_handshake()
ssl.SSLError: [SSL: SSLV3_ALERT_HANDSHAKE_FAILURE] sslv3 alert handshake failure (_ssl.c:777)
During handling of the above exception, another exception occurred:
Traceback (most recent call last):
  File "/home/travis/build/h3llrais3r/Auto-Subliminal/lib/requests/adapters.py", line 449, in send
    timeout=timeout
  File "/home/travis/build/h3llrais3r/Auto-Subliminal/lib/urllib3/connectionpool.py", line 641, in urlopen
    _stacktrace=sys.exc_info()[2])
  File "/home/travis/build/h3llrais3r/Auto-Subliminal/lib/urllib3/util/retry.py", line 399, in increment
    raise MaxRetryError(_pool, url, error or ResponseError(cause))
urllib3.exceptions.MaxRetryError: HTTPSConnectionPool(host='v2.sg.media-imdb.com', port=443): Max retries exceeded with url: /suggests/s/Southpaw.json (Caused by SSLError(SSLError(1, '[SSL: SSLV3_ALERT_HANDSHAKE_FAILURE] sslv3 alert handshake failure (_ssl.c:777)'),))
During handling of the above exception, another exception occurred:
Traceback (most recent call last):
  File "/home/travis/build/h3llrais3r/Auto-Subliminal/autosubliminal/indexer.py", line 351, in get_imdb_id_and_year
    api_obj = self._search(title, year)
  File "/home/travis/build/h3llrais3r/Auto-Subliminal/autosubliminal/indexer.py", line 273, in _search
    search_results = ImdbFacade().search_for_title(title)
  File "/home/travis/build/h3llrais3r/Auto-Subliminal/lib/imdbpie/facade.py", line 87, in search_for_title
    for result in self._client.search_for_title(query):
  File "/home/travis/build/h3llrais3r/Auto-Subliminal/lib/imdbpie/imdbpie.py", line 182, in search_for_title
    search_results = self._suggest_search(title)
  File "/home/travis/build/h3llrais3r/Auto-Subliminal/lib/imdbpie/imdbpie.py", line 160, in _suggest_search
    search_results = self._get(url=url, query=query_encoded)
  File "/home/travis/build/h3llrais3r/Auto-Subliminal/lib/imdbpie/imdbpie.py", line 308, in _get
    resp = self.session.get(url, headers=headers, params=params)
  File "/home/travis/build/h3llrais3r/Auto-Subliminal/lib/requests/sessions.py", line 546, in get
    return self.request('GET', url, **kwargs)
  File "/home/travis/build/h3llrais3r/Auto-Subliminal/lib/requests/sessions.py", line 533, in request
    resp = self.send(prep, **send_kwargs)
  File "/home/travis/build/h3llrais3r/Auto-Subliminal/lib/requests/sessions.py", line 646, in send
    r = adapter.send(request, **kwargs)
  File "/home/travis/build/h3llrais3r/Auto-Subliminal/lib/requests/
... (truncated) ...

Environment

Python: 3.6

What Broke

Users experience SSL handshake failures when connecting to certain hosts, leading to failed requests.

Why It Broke

The SSL handshake failure occurs due to incorrect detection of IPvFuture addresses

Fix Options (Details)

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

pip install urllib3==1.25.2

When NOT to use: This fix should not be applied if the application requires support for IPvFuture addresses.

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/1583

First fixed release: 1.25.2

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

When NOT to Use This Fix

This fix should not be applied if the application requires support for IPvFuture addresses.

Verify Fix

verify

Re-run the minimal reproduction on your broken version, then apply the fix and re-run.

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
1.25.2	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 SSLV3_ALERT_HANDSHAKE_FAILURE after upgrading to v1.25.x (Fix)