urllib3 SSLError (Fix)

The Fix

pip install urllib3==1.25.11

Based on closed urllib3/urllib3 issue #1764 · 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

@@ -22,6 +22,7 @@
     InvalidHeader,
     HTTPError,
+    SSLError,
 )
 from .packages.six import string_types as basestring, PY3

repro.py

Traceback (most recent call last):
  File "/home/web/web/yandex/.env/lib/python3.5/site-packages/ioweb/network_service.py", line 177, in thread_network
    req, res, error, raise_network_error=False
  File "/home/web/web/yandex/.env/lib/python3.5/site-packages/ioweb/transport.py", line 310, in prepare_response
    self.read_with_timeout(req, res)
  File "/home/web/web/yandex/.env/lib/python3.5/site-packages/ioweb/transport.py", line 266, in read_with_timeout
    chunk = self.urllib3_response.read(chunk_size)
  File "/home/web/web/yandex/.env/lib/python3.5/site-packages/urllib3/response.py", line 507, in read
    data = self._fp.read(amt) if not fp_closed else b""
  File "/usr/lib/python3.5/http/client.py", line 448, in read
    n = self.readinto(b)
  File "/usr/lib/python3.5/http/client.py", line 478, in readinto
    return self._readinto_chunked(b)
  File "/usr/lib/python3.5/http/client.py", line 573, in _readinto_chunked
    chunk_left = self._get_chunk_left()
  File "/usr/lib/python3.5/http/client.py", line 541, in _get_chunk_left
    chunk_left = self._read_next_chunk_size()
  File "/usr/lib/python3.5/http/client.py", line 501, in _read_next_chunk_size
    line = self.fp.readline(_MAXLINE + 1)
  File "/usr/lib/python3.5/socket.py", line 576, in readinto
    return self._sock.recv_into(b)
  File "/home/web/web/yandex/.env/lib/python3.5/site-packages/urllib3/contrib/pyopenssl.py", line 332, in recv_into
    raise ssl.SSLError("read error: %r" % e)
ssl.SSLError: ("read error: Error([('SSL routines', 'ssl3_get_record', 'decryption failed or bad record mac')],)",)

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==1.25.11\nWhen NOT to use: Do not use this fix if you require the original SSLError behavior for debugging.\n\n

Why This Fix Works in Production

Trigger: req, res, error, raise_network_error=False
Mechanism: urllib3 is allowing an SSLError to escape without proper wrapping
Why the fix works: Wraps BaseSSLError into SSLError during response reads to ensure proper exception handling. (first fixed release: 1.25.11).

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 3.5 in real deployments (not just unit tests).
urllib3 is allowing an SSLError to escape without proper wrapping
Surfaces as: Traceback (most recent call last):

Proof / Evidence

GitHub issue: #1764
Fix PR: https://github.com/urllib3/urllib3/pull/1939
First fixed release: 1.25.11
Reproduced locally: No (not executed)
Last verified: 2026-02-09
Confidence: 0.95
Did this fix it?: Yes (upstream fix exists)
Own content ratio: 0.29

Discussion

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

Jump to Sources Open on GitHub

“@christopher-hesse I believe you're correct, we should be wrapping the BaseSSLError into a urllib3.exceptions.SSLError in line with the _error_catcher() contract of wrapping low-level Python exceptions…”

@sethmlarson · 2020-06-14 · source

“Hi @lorien! Can you please submit a simple reproducing script?”

@hodbn · 2020-04-27 · source

“It looks like urllib3.exceptions.SSLError says Raised when SSL certificate fails in an HTTPS connection”

@christopher-hesse · 2020-06-14 · source

“I've seen this error as well”

@christopher-hesse · 2020-06-14 · source

Failure Signature (Search String)

req, res, error, raise_network_error=False

Error Message

Stack trace

error.txt

Error Message
-------------
Traceback (most recent call last):
  File "/home/web/web/yandex/.env/lib/python3.5/site-packages/ioweb/network_service.py", line 177, in thread_network
    req, res, error, raise_network_error=False
  File "/home/web/web/yandex/.env/lib/python3.5/site-packages/ioweb/transport.py", line 310, in prepare_response
    self.read_with_timeout(req, res)
  File "/home/web/web/yandex/.env/lib/python3.5/site-packages/ioweb/transport.py", line 266, in read_with_timeout
    chunk = self.urllib3_response.read(chunk_size)
  File "/home/web/web/yandex/.env/lib/python3.5/site-packages/urllib3/response.py", line 507, in read
    data = self._fp.read(amt) if not fp_closed else b""
  File "/usr/lib/python3.5/http/client.py", line 448, in read
    n = self.readinto(b)
  File "/usr/lib/python3.5/http/client.py", line 478, in readinto
    return self._readinto_chunked(b)
  File "/usr/lib/python3.5/http/client.py", line 573, in _readinto_chunked
    chunk_left = self._get_chunk_left()
  File "/usr/lib/python3.5/http/client.py", line 541, in _get_chunk_left
    chunk_left = self._read_next_chunk_size()
  File "/usr/lib/python3.5/http/client.py", line 501, in _read_next_chunk_size
    line = self.fp.readline(_MAXLINE + 1)
  File "/usr/lib/python3.5/socket.py", line 576, in readinto
    return self._sock.recv_into(b)
  File "/home/web/web/yandex/.env/lib/python3.5/site-packages/urllib3/contrib/pyopenssl
... (truncated) ...

Minimal Reproduction

repro.py

Traceback (most recent call last):
  File "/home/web/web/yandex/.env/lib/python3.5/site-packages/ioweb/network_service.py", line 177, in thread_network
    req, res, error, raise_network_error=False
  File "/home/web/web/yandex/.env/lib/python3.5/site-packages/ioweb/transport.py", line 310, in prepare_response
    self.read_with_timeout(req, res)
  File "/home/web/web/yandex/.env/lib/python3.5/site-packages/ioweb/transport.py", line 266, in read_with_timeout
    chunk = self.urllib3_response.read(chunk_size)
  File "/home/web/web/yandex/.env/lib/python3.5/site-packages/urllib3/response.py", line 507, in read
    data = self._fp.read(amt) if not fp_closed else b""
  File "/usr/lib/python3.5/http/client.py", line 448, in read
    n = self.readinto(b)
  File "/usr/lib/python3.5/http/client.py", line 478, in readinto
    return self._readinto_chunked(b)
  File "/usr/lib/python3.5/http/client.py", line 573, in _readinto_chunked
    chunk_left = self._get_chunk_left()
  File "/usr/lib/python3.5/http/client.py", line 541, in _get_chunk_left
    chunk_left = self._read_next_chunk_size()
  File "/usr/lib/python3.5/http/client.py", line 501, in _read_next_chunk_size
    line = self.fp.readline(_MAXLINE + 1)
  File "/usr/lib/python3.5/socket.py", line 576, in readinto
    return self._sock.recv_into(b)
  File "/home/web/web/yandex/.env/lib/python3.5/site-packages/urllib3/contrib/pyopenssl.py", line 332, in recv_into
    raise ssl.SSLError("read error: %r" % e)
ssl.SSLError: ("read error: Error([('SSL routines', 'ssl3_get_record', 'decryption failed or bad record mac')],)",)

Environment

Python: 3.5

What Broke

Users experience unhandled SSLError during response reads, causing application crashes.

Why It Broke

urllib3 is allowing an SSLError to escape without proper wrapping

Fix Options (Details)

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

pip install urllib3==1.25.11

When NOT to use: Do not use this fix if you require the original SSLError behavior for debugging.

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/1939

First fixed release: 1.25.11

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

When NOT to Use This Fix

Do not use this fix if you require the original SSLError behavior for debugging.

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
1.25.11	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.