urllib3 parse_retry_after() in utils/retry.py computes

The Fix

pip install urllib3==1.25.11

Based on closed urllib3/urllib3 issue #1896 · PR/commit linked

Jump to Verify Open PR/Commit

@@ -7,6 +7,7 @@ PySocks==1.7.1
 pytest==4.6.9
 pytest-timeout==1.3.4
+pytest-freezegun==0.3.0.post1
 flaky==3.6.1
 trustme==0.5.3

repro.py

import re
import time
import email.utils
import datetime



def parse_retry_after(retry_after):
    """
    Pulled from retry.py and minimally modified to change exception raised.
    """
    # Whitespace: https://tools.ietf.org/html/rfc7230#section-3.2.4
    if re.match(r"^\s*[0-9]+\s*$", retry_after):
        seconds = int(retry_after)
    else:
        retry_date_tuple = email.utils.parsedate(retry_after)
        if retry_date_tuple is None:
            raise RuntimeError('Invalid header!')
        retry_date = time.mktime(retry_date_tuple)
        seconds = retry_date - time.time()

    if seconds < 0:
        seconds = 0

    return seconds


if __name__ == '__main__':
    # Create a Retry-After value (http-date) that's 180 seconds after now.  Note this will only
    # demonstrate the issue when the local timezone is *not* GMT.
    nowutc = datetime.datetime.now(datetime.timezone.utc) + datetime.timedelta(seconds=180)
    retryafter = nowutc.strftime('%a, %d %b %Y %H:%M:%S GMT ')

    print(f'got {parse_retry_after(retryafter)} for {retryafter}, '
          f'but should be {nowutc.timestamp() - time.time()}')

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: This fix should not be used if maintaining backward compatibility with incorrect time zone handling is required.\n\n

Why This Fix Works in Production

Trigger: For the given Retry-After value `Thu, 25 Jun 2020 21:30:12 GMT`, with the local time being `Thu, 25 Jun 2020 17:28:12 EST`, parse_retry_after() will return…
Mechanism: parse_retry_after() does not handle time zone differences correctly when parsing Retry-After values
Why the fix works: Updates the parse_retry_after function to use timezone-aware functions for better handling of Retry-After values, addressing the issue of incorrect time zone conversion. (first fixed release: 1.25.11).

Production impact:

If left unfixed, this can cause silent data inconsistencies that propagate (bad cache entries, incorrect downstream decisions).

Why This Breaks in Prod

parse_retry_after() does not handle time zone differences correctly when parsing Retry-After values
Production symptom (often without a traceback): For the given Retry-After value `Thu, 25 Jun 2020 21:30:12 GMT`, with the local time being `Thu, 25 Jun 2020 17:28:12 EST`, parse_retry_after() will return `14564.671981096268`. This value is incorrect, and should be `~120`.

Proof / Evidence

GitHub issue: #1896
Fix PR: https://github.com/urllib3/urllib3/pull/1932
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: 0.52

Discussion

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

Jump to Sources Open on GitHub

“This seems to fix the issue, but I've not done near enough testing or tried any python version other than 3.6.8:”

@cblades-tc · 2020-06-26 · source

“Here's a MRE that pulls out the code of parse_retry_after().”

@cblades-tc · 2020-06-25 · source

“Thanks for opening this, will look at it later. Going to summon the timezone wizard @pganssle for assistance making sense of this.”

@sethmlarson · 2020-06-25 · source

“@cblades-tc Would you be willing to submit a patch with a previously failing test case?”

@sethmlarson · 2020-06-26 · source

Failure Signature (Search String)

For the given Retry-After value `Thu, 25 Jun 2020 21:30:12 GMT`, with the local time being `Thu, 25 Jun 2020 17:28:12 EST`, parse_retry_after() will return `14564.671981096268`.
parse_retry_after() doesn't correctly handle the time difference between time zones.

Copy-friendly signature

signature.txt

Failure Signature
-----------------
For the given Retry-After value `Thu, 25 Jun 2020 21:30:12 GMT`, with the local time being `Thu, 25 Jun 2020 17:28:12 EST`, parse_retry_after() will return `14564.671981096268`.  This value is incorrect, and should be `~120`.
parse_retry_after() doesn't correctly handle the time difference between time zones.

Error Message

Signature-only (no traceback captured)

error.txt

Error Message
-------------
For the given Retry-After value `Thu, 25 Jun 2020 21:30:12 GMT`, with the local time being `Thu, 25 Jun 2020 17:28:12 EST`, parse_retry_after() will return `14564.671981096268`.  This value is incorrect, and should be `~120`.
parse_retry_after() doesn't correctly handle the time difference between time zones.

Minimal Reproduction

repro.py

import re
import time
import email.utils
import datetime



def parse_retry_after(retry_after):
    """
    Pulled from retry.py and minimally modified to change exception raised.
    """
    # Whitespace: https://tools.ietf.org/html/rfc7230#section-3.2.4
    if re.match(r"^\s*[0-9]+\s*$", retry_after):
        seconds = int(retry_after)
    else:
        retry_date_tuple = email.utils.parsedate(retry_after)
        if retry_date_tuple is None:
            raise RuntimeError('Invalid header!')
        retry_date = time.mktime(retry_date_tuple)
        seconds = retry_date - time.time()

    if seconds < 0:
        seconds = 0

    return seconds


if __name__ == '__main__':
    # Create a Retry-After value (http-date) that's 180 seconds after now.  Note this will only
    # demonstrate the issue when the local timezone is *not* GMT.
    nowutc = datetime.datetime.now(datetime.timezone.utc) + datetime.timedelta(seconds=180)
    retryafter = nowutc.strftime('%a, %d %b %Y %H:%M:%S GMT ')

    print(f'got {parse_retry_after(retryafter)} for {retryafter}, '
          f'but should be {nowutc.timestamp() - time.time()}')

What Broke

Incorrect Retry-After values lead to unexpected delays in request retries, causing potential timeouts.

Why It Broke

parse_retry_after() does not handle time zone differences correctly when parsing Retry-After values

Fix Options (Details)

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

pip install urllib3==1.25.11

When NOT to use: This fix should not be used if maintaining backward compatibility with incorrect time zone handling is required.

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/1932

First fixed release: 1.25.11

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

When NOT to Use This Fix

This fix should not be used if maintaining backward compatibility with incorrect time zone handling is required.

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.

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Related clusters: Configuration error SSL handshake Other

Sources

We don’t republish the full GitHub discussion text. Use the links above for context.

urllib3 parse_retry_after() in utils/retry.py computes seconds incorrectly when Retry-After value (Fix)