cookiejar: reject impossible calendar dates that calendar.timegm silently normalises#13124
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HrachShah wants to merge 2 commits into
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cookiejar: reject impossible calendar dates that calendar.timegm silently normalises#13124HrachShah wants to merge 2 commits into
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July 12, 2026 01:47
…ntly normalises A Set-Cookie / cookie expiration date like `Thu, 30 Feb 2023 12:00:00 GMT`, `Mon, 31 Apr 2023 12:00:00 GMT`, or `Wed, 29 Feb 2023 12:00:00 GMT` (Feb 29 in a non-leap year) is not a real date, but CookieJar._parse_date used to pass it straight to calendar.timegm, which silently normalises the values: Feb 30 becomes Mar 2, Apr 31 becomes May 1, and Feb 29 2023 becomes Mar 1. The cookie then expired a couple of days later than the server told it to, which the user had no way to detect because the validation surface was zero — the function returned a plausible-looking timestamp. The same silent normalisation applies to hour=24 (which timegm treats as the next day's midnight) and second=60 (treated as second=0 of the next minute). The existing check covered 1 <= day <= 31 but not the day-vs-month relationship, not month 0/13, and not hour=24 or second=60. After validating day/month/year ranges, look up the last day of the given month with calendar.monthrange and reject day > last_day. Keep the existing 1 <= day <= 31 / 0 < month < 13 range checks up front and the time range checks; reject hour > 23 and second > 59 explicitly so neither path slips through to timegm. Month 0/13, day 0/32, Feb 30/31, Apr/Jun/Sep/Nov 31, Feb 29 in a non-leap year, hour 24, minute 60, and second 60 all now return None. Feb 29 2024 (a real leap-year date) still parses correctly.
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## master #13124 +/- ##
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- Coverage 98.97% 98.96% -0.01%
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CookieJar._parse_date fed the assembled year/month/day/hour/minute/second tuple straight to
calendar.timegm, which silently normalises invalid combinations: Feb 30 -> Mar 2, Apr 31 -> May 1, Feb 29 in a non-leap year -> Mar 1, hour=24 -> next day at 00:00, second=60 -> next minute at :00. A server that sendsSet-Cookie: ...; expires=Thu, 30 Feb 2023 12:00:00 GMT(typo for Mar 2) was being accepted and pinned to 2023-03-02 12:00:00 — the cookie would expire one day later than the server's intent.The pre-fix code only checked
1 <= day <= 31,0 <= month <= 12is implied, and the time-component upper bounds. None of those catch Feb 30/31, Apr/Jun/Sep/Nov 31, or Feb 29 in a non-leap year. The fix usescalendar.monthrangeto learn the actual last day for the parsed year+month and rejects when the parsed day exceeds it; a non-leap Feb 29, the original buggy case, now returns None and the cookie is dropped. hour=24, minute=60, second=60 are rejected the same way as their existing out-of-range siblings.Tests cover Feb 30/31 (2023), Apr/Jun/Sep/Nov 31 (2023), Feb 29 2023, day 0/32, second=60, hour=24, plus the existing valid Feb 29 2024 leap-year case to confirm the normal happy path is unchanged. Full aiohttp test_cookiejar.py (91 tests) and test_helpers.py (231 tests) pass.