Merge pull request #902 from mozilla/proxy_drop_exfil_domain

Create an alert on attempts to use known exfil domains

alerts/proxy_drop_exfil_domains.conf

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+[options]
+exfil_domains = pastebin.com,www.sendspace.com

alerts/proxy_drop_exfil_domains.py

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+#!/usr/bin/env python
+
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+# Copyright (c) 2014 Mozilla Corporation
+
+
+from lib.alerttask import AlertTask
+from mozdef_util.query_models import SearchQuery, TermMatch, QueryStringMatch, ExistsMatch, PhraseMatch, WildcardMatch
+
+
+class AlertProxyDropExfilDomains(AlertTask):
+    def main(self):
+        self.parse_config('proxy_drop_exfil_domains.conf', ['exfil_domains'])
+
+        search_query = SearchQuery(minutes=20)
+
+        search_query.add_must([
+            TermMatch('category', 'squid'),
+            TermMatch('tags', 'squid'),
+            TermMatch('details.proxyaction', "TCP_DENIED/-")
+        ])
+
+        # Only notify on certain domains listed in the config
+        domain_regex = "/({0}).*/".format(
+            self.config.exfil_domains.replace(',', '|'))
+        search_query.add_must([
+            QueryStringMatch('details.destination: {}'.format(domain_regex))
+        ])
+
+        self.filtersManual(search_query)
+
+        # Search aggregations on field 'hostname', keep X samples of
+        # events at most
+        self.searchEventsAggregated('details.sourceipaddress', samplesLimit=10)
+        # alert when >= X matching events in an aggregation
+        # I think it makes sense to alert every time here
+        self.walkAggregations(threshold=1)
+
+    # Set alert properties
+    def onAggregation(self, aggreg):
+        # aggreg['count']: number of items in the aggregation, ex: number of failed login attempts
+        # aggreg['value']: value of the aggregation field, ex: toto@example.com
+        # aggreg['events']: list of events in the aggregation
+        category = 'squid'
+        tags = ['squid', 'proxy']
+        severity = 'WARNING'
+
+        exfil_domains = set()
+        for event in aggreg['allevents']:
+            domain = event['_source']['details']['destination'].split(':')
+            exfil_domains.add(domain[0])
+
+        summary = 'Suspicious Proxy DROP event(s) detected from {0} to the following exfil domain(s): {1}'.format(
+            aggreg['value'],
+            ",".join(sorted(exfil_domains))
+        )
+
+        # Create the alert object based on these properties
+        return self.createAlertDict(summary, category, tags, aggreg['events'], severity)

tests/alerts/test_proxy_drop_exfil_domains.py

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+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+# Copyright (c) 2017 Mozilla Corporation
+from positive_alert_test_case import PositiveAlertTestCase
+from negative_alert_test_case import NegativeAlertTestCase
+from alert_test_suite import AlertTestSuite
+
+
+class TestProxyDropExfilDomains(AlertTestSuite):
+    alert_filename = "proxy_drop_exfil_domains"
+    alert_classname = "AlertProxyDropExfilDomains"
+
+    # This event is the default positive event that will cause the
+    # alert to trigger
+    default_event = {
+        "_type": "event",
+        "_source": {
+            "category": "squid",
+            "tags": ["squid"],
+            "details": {
+                "sourceipaddress": "1.2.3.4",
+                "destination": "pastebin.com",
+                "proxyaction": "TCP_DENIED/-",
+            }
+        }
+    }
+
+    # This event is an alternate destination that we'd want to aggregate
+    default_event2 = AlertTestSuite.copy(default_event)
+    default_event2["_source"]["details"]["destination"] = "www.sendspace.com"
+
+    # This event is the default negative event that will not cause the
+    # alert to trigger
+    default_negative_event = AlertTestSuite.copy(default_event)
+    default_negative_event["_source"]["details"]["destination"] = "foo.mozilla.com"
+
+    # This alert is the expected result from running this task
+    default_alert = {
+        "category": "squid",
+        "tags": ['squid', 'proxy'],
+        "severity": "WARNING",
+        "summary": 'Suspicious Proxy DROP event(s) detected from 1.2.3.4 to the following exfil domain(s): pastebin.com',
+    }
+
+    # This alert is the expected result from this task against multiple matching events
+    default_alert_aggregated = AlertTestSuite.copy(default_alert)
+    default_alert_aggregated[
+        "summary"] = 'Suspicious Proxy DROP event(s) detected from 1.2.3.4 to the following exfil domain(s): pastebin.com,www.sendspace.com'
+
+    test_cases = []
+
+    test_cases.append(
+        PositiveAlertTestCase(
+            description="Positive test with default events and default alert expected",
+            events=AlertTestSuite.create_events(default_event, 1),
+            expected_alert=default_alert
+        )
+    )
+
+    test_cases.append(
+        PositiveAlertTestCase(
+            description="Positive test with default events and default alert expected - dedup",
+            events=AlertTestSuite.create_events(default_event, 2),
+            expected_alert=default_alert
+        )
+    )
+
+    events1 = AlertTestSuite.create_events(default_event, 1)
+    events2 = AlertTestSuite.create_events(default_event2, 1)
+    test_cases.append(
+        PositiveAlertTestCase(
+            description="Positive test with default events and default alert expected - different destinations",
+            events=events1 + events2,
+            expected_alert=default_alert_aggregated
+        )
+    )
+
+    test_cases.append(
+        NegativeAlertTestCase(
+            description="Negative test with default negative event",
+            events=AlertTestSuite.create_events(default_negative_event, 1),
+        )
+    )
+
+    events = AlertTestSuite.create_events(default_event, 10)
+    for event in events:
+        event['_source']['category'] = 'bad'
+    test_cases.append(
+        NegativeAlertTestCase(
+            description="Negative test case with events with incorrect category",
+            events=events,
+        )
+    )
+
+    events = AlertTestSuite.create_events(default_event, 10)
+    for event in events:
+        event['_source']['tags'] = 'bad tag example'
+    test_cases.append(
+        NegativeAlertTestCase(
+            description="Negative test case with events with incorrect tags",
+            events=events,
+        )
+    )
+    events = AlertTestSuite.create_events(default_event, 10)
+    for event in events:
+        event['_source']['utctimestamp'] = AlertTestSuite.subtract_from_timestamp_lambda({
+                                                                                         'minutes': 241})
+        event['_source']['receivedtimestamp'] = AlertTestSuite.subtract_from_timestamp_lambda({
+                                                                                              'minutes': 241})
+    test_cases.append(
+        NegativeAlertTestCase(
+            description="Negative test case with old timestamp",
+            events=events,
+        )
+    )