OSSIM傳感器Agent傳送機制初探

OSSIM Agent的主要職責是收集網絡上存在的各種設備發送的所有數據，然後按照一種標準方式有序發給OSSIM Server，Agent收集到數據後在發送給Server之前要對這些數據進行歸一化處理，本文主要就如何有序發送數據與如何完成歸一化進行討論。
OSSIM傳感器在通過GET框架實現OSSIM代理和OSSIM服務器之間通信協議和數據格式的之間轉換。下面我們先簡要看一下ossim-agent腳本：
#!/usr/bin/python -OOt
import sys
sys.path.append('/usr/share/ossim-agent/')
sys.path.append('/usr/local/share/ossim-agent/')
from ossim_agent.Agent import Agent
agent = Agent()
agent.main()
這裏需要GET作爲OSSIM代理向OSSIM服務器輸送數據。實現緊密整合所需的兩個主要操作是“生成”（或）OSSIM兼容事件的“映射Mapping”）和此類數據向OSSIM的“傳輸”服務器。它負責此類操作的GET框架的兩個組件是EventHandler和Sender Agent，如圖1所示。

圖1 將Get框架內容集成到OSSIM

Event Handler的主要任務是映射數據源插件採集的事件到SIEM實例警報的OSSIM標準化事件格式。爲了執行這樣的過程，原始消息經歷由RAW LOG轉換爲現有歸一化數據字段格式的一個轉變；在上圖中我們將這些機制表示爲“歸一化Normalization”和“OSSIM消息”。部分日誌歸一化代碼：

from Logger import Logger
from time import mktime, strptime
logger = Logger.logger
class Event:
    EVENT_TYPE = 'event'
    EVENT_ATTRS = [
        "type",
        "date",
        "sensor",
        "interface",
        "plugin_id",
        "plugin_sid",
        "priority",
        "protocol",
        "src_ip",
        "src_port",
        "dst_ip",
        "dst_port",
        "username",
        "password",
        "filename",
        "userdata1",
        "userdata2",
        "userdata3",
        "userdata4",
        "userdata5",
        "userdata6",
        "userdata7",
        "userdata8",
        "userdata9",
        "occurrences",
        "log",
        "data",
        "snort_sid",    # snort specific
        "snort_cid",    # snort specific
        "fdate",
        "tzone"
    ]

    def __init__(self):
        self.event = {}
        self.event["event_type"] = self.EVENT_TYPE

    def __setitem__(self, key, value):

        if key in self.EVENT_ATTRS:
            self.event[key] = self.sanitize_value(value)
            if key == "date":
                # 以秒爲單位
                self.event["fdate"]=self.event[key]
                try:
                    self.event["date"]=int(mktime(strptime(self.event[key],"%Y-%m-%d %H:%M:%S")))
                except:
                    logger.warning("There was an error parsing date (%s)" %\
                        (self.event[key]))
        elif key != 'event_type':
            logger.warning("Bad event attribute: %s" % (key))

    def __getitem__(self, key):
        return self.event.get(key, None)
    # 事件表示
    def __repr__(self):
        event = self.EVENT_TYPE
        for attr in self.EVENT_ATTRS:
            if self[attr]:
                event += ' %s="%s"' % (attr, self[attr])
        return event + "\n"
    # 返回內部哈希值
    def dict(self):
        return self.event

    def sanitize_value(self, string):
        return str(string).strip().replace("\"", "\\\"").replace("'", "")

class EventOS(Event):
    EVENT_TYPE = 'host-os-event'
    EVENT_ATTRS = [
        "host",
        "os",
        "sensor",
        "interface",
        "date",
        "plugin_id",
        "plugin_sid",
        "occurrences",
        "log",
        "fdate",
    ]

class EventMac(Event):
    EVENT_TYPE = 'host-mac-event'
    EVENT_ATTRS = [
        "host",
        "mac",
        "vendor",
        "sensor",
        "interface",
        "date",
        "plugin_id",
        "plugin_sid",
        "occurrences",
        "log",
        "fdate",
    ]

class EventService(Event):
    EVENT_TYPE = 'host-service-event'
    EVENT_ATTRS = [
        "host",
        "sensor",
        "interface",
        "port",
        "protocol",
        "service",
        "application",
        "date",
        "plugin_id",
        "plugin_sid",
        "occurrences",
        "log",
        "fdate",
    ]

class EventHids(Event):
    EVENT_TYPE = 'host-ids-event'
    EVENT_ATTRS = [
        "host",
        "hostname",
        "hids_event_type",
        "target",
        "what",
        "extra_data",
        "sensor",
        "date",
        "plugin_id",
        "plugin_sid",
        "username",
        "password",
        "filename",
        "userdata1",
        "userdata2",
        "userdata3",
        "userdata4",
        "userdata5",
        "userdata6",
        "userdata7",
        "userdata8",
        "userdata9",
        "occurrences",
        "log",
        "fdate",
    ]

class WatchRule(Event):

    EVENT_TYPE = 'event'
    EVENT_ATTRS = [
        "type",
    "date",
    "fdate",
    "sensor",
    "interface",
    "src_ip",
    "dst_ip",
    "protocol",
        "plugin_id",
        "plugin_sid",
        "condition",
        "value",
        "port_from",
        "src_port",
        "port_to",
        "dst_port",
        "interval",
        "from",
        "to",
        "absolute",
    "log",
        "userdata1",
        "userdata2",
        "userdata3",
        "userdata4",
        "userdata5",
        "userdata6",
        "userdata7",
        "userdata8",
        "userdata9",
        "filename",
        "username",
    ]
class Snort(Event):
    EVENT_TYPE = 'snort-event'
    EVENT_ATTRS = [
        "sensor",
        "interface",
        "gzipdata",
        "unziplen",
        "event_type",
        "plugin_id",
        "type",
        "occurrences"
    ]

日誌編碼代碼：

import threading, time
from Logger import Logger
logger = Logger.logger
from Output import Output
import Config
import Event
from Threshold import EventConsolidation
from Stats import Stats
from ConnPro import ServerConnPro
class Detector(threading.Thread):
    def __init__(self, conf, plugin, conn):

        self._conf = conf
        self._plugin = plugin
        self.os_hash = {}
        self.conn = conn
        self.consolidation = EventConsolidation(self._conf)
        logger.info("Starting detector %s (%s).." % \
                    (self._plugin.get("config", "name"),
                     self._plugin.get("config", "plugin_id")))
        threading.Thread.__init__(self)
    def _event_os_cached(self, event):
        if isinstance(event, Event.EventOS):
            import string
            current_os = string.join(string.split(event["os"]), ' ')
            previous_os = self.os_hash.get(event["host"], '')
            if current_os == previous_os:
                return True
            else:
                # 失敗並添加到緩存
                self.os_hash[event["host"]] = \
                    string.join(string.split(event["os"]), ' ')
        return False
    def _exclude_event(self, event):

        if self._plugin.has_option("config", "exclude_sids"):
            exclude_sids = self._plugin.get("config", "exclude_sids")
            if event["plugin_sid"] in Config.split_sids(exclude_sids):
                logger.debug("Excluding event with " +\
                    "plugin_id=%s and plugin_sid=%s" %\
                    (event["plugin_id"], event["plugin_sid"]))
                return True
        return False

    def _thresholding(self):
        self.consolidation.process()
    def _plugin_defaults(self, event):
        # 從配置文件中獲取默認參數
        if self._conf.has_section("plugin-defaults"):

        # 1) 日期
            default_date_format = self._conf.get("plugin-defaults",
                                                 "date_format")
            if event["date"] is None and default_date_format and \
               'date' in event.EVENT_ATTRS:
                event["date"] = time.strftime(default_date_format, 
                                              time.localtime(time.time()))
        # 2) 傳感器
            default_sensor = self._conf.get("plugin-defaults", "sensor")
            if event["sensor"] is None and default_sensor and \
               'sensor' in event.EVENT_ATTRS:
                event["sensor"] = default_sensor
        # 3) 網絡接口
            default_iface = self._conf.get("plugin-defaults", "interface")
            if event["interface"] is None and default_iface and \
               'interface' in event.EVENT_ATTRS:
                event["interface"] = default_iface
        # 4) 源IP
            if event["src_ip"] is None and 'src_ip' in event.EVENT_ATTRS:
                event["src_ip"] = event["sensor"]
        # 5) 時區
            default_tzone = self._conf.get("plugin-defaults", "tzone")
            if event["tzone"] is None and 'tzone' in event.EVENT_ATTRS:
                event["tzone"] = default_tzone

        # 6) sensor,source ip and dest != localhost
            if event["sensor"] in ('127.0.0.1', '127.0.1.1'):
                event["sensor"] = default_sensor

            if event["dst_ip"] in ('127.0.0.1', '127.0.1.1'):
                event["dst_ip"] = default_sensor

            if event["src_ip"] in ('127.0.0.1', '127.0.1.1'):
                event["src_ip"] = default_sensor
        # 檢測日誌的類型
        if event["type"] is None and 'type' in event.EVENT_ATTRS:
            event["type"] = 'detector'
        return event
    def send_message(self, event):
        if self._event_os_cached(event):
            return

        if self._exclude_event(event):
            return
        #對於一些空屬性使用默認值。
        event = self._plugin_defaults(event)

        # 合併之前檢查
        if self.conn is not None:
            try:
                self.conn.send(str(event))
            except:
                id = self._plugin.get("config", "plugin_id")
                c = ServerConnPro(self._conf, id)
                self.conn = c.connect(0, 10)
                try:
                    self.conn.send(str(event))
                except:
                    return
            logger.info(str(event).rstrip())
        elif not self.consolidation.insert(event):
            Output.event(event)
        Stats.new_event(event)
    def stop(self):
        #self.consolidation.clear()
        pass
#在子類中重寫
    def process(self):
        pass
    def run(self):
        self.process()
class ParserSocket(Detector):
    def process(self):
        self.process()
class ParserDatabase(Detector):
    def process(self):
        self.process()

… …

從上可以看出，傳感器的歸一化主要負責對每個LOG內數據字段進行重新編碼，使其生成一個全新的可能用於發送到OSSIM服務器的完整事件。爲達成這種目的GET框架中包含了一些特定的功能，以便將所有的功能轉換需要BASE64轉換的字段。“OSSIM消息”負責填充GET生成的原始事件中不存在的字段。所以上面講的plugin_id、plugin_sid是用來表示日誌消息來源類型和子類型，這也是生成SIEM事件的必填字段。爲事件格式完整性考慮，有些時候在無法確認源或目標IP時，系統默認會採用0.0.0.0來填充該字段。

注意：這種必填字段我們可利用phpmyadmin工具查看OSSIM的MySQL數據庫。
Sender Agent負責完成下面兩個任務：
發送由GET收集並由事件格式化的事件發送到OSSIM服務器，這項任務由Event Hander創建的消息組成消息隊列發送到消息中間件實現，時序圖如圖2所示。

圖2 序列圖：從安全探測器的日誌轉換到OSSIM服務器事件

2）管理GET框架和OSSIM服務器之間的通信，通信端口爲TCP 40001通過雙向握手實現。歸一化原始日誌是規範化過程的一個重要環節，OSSIM在歸一化處理日誌的同時保留了原始日誌，可用於日誌歸檔，提供了一種從規範化事件中提取原始日誌的手段。
經過歸一化處理的EVENTS，存儲到MySQL數據庫中，如圖3所示。接着就由關聯引擎根據規則、優先級、可靠性等參數進行交叉關聯分析，得出風險值併發出各種報警提示信息。

圖3 日誌存儲機制
接下來我們再看個實例，下面是一段Apache、CiscoASA以及SSH的原始日誌，如圖4、圖5、圖6所示。

Apache插件中的正則表達式：
[0001 - apache-access] 訪問日誌

event_type=event
regexp=((?P\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3})(:(?P\d{1,5}))? )?(?P\S+) (?P\S+) (?P\S+) \[(?P\d{2}\/\w{3}\/\d{4}:\d{2}:\d{2}:\d{2})\s+[+-]\d{4}\] \"(?P[^\"]*)\" (?P\d{3}) ((?P\d+)|-)( \"(?P[^\"]*)\" \"(?P[^\"]*)\")?$
src_ip={resolv($src)}
dst_ip={resolv($dst)}
dst_port={$port}
date={normalize_date($date)}
plugin_sid={$code}
username={$user}
userdata1={$request}
userdata2={$size}
userdata3={$referer_uri}
userdata4={$useragent}
filename={$id}

[0002 - apache-error] 錯誤日誌

event_type=event
regexp=\[(?P\w{3} \w{3} \d{2} \d{2}:\d{2}:\d{2} \d{4})\] \[(?P(emerg|alert|crit|error|warn|notice|info|debug))\] (\[client (?P\S+)\] )?(?P.*)
date={normalize_date($date)}
plugin_sid={translate($type)}
src_ip={resolv($src)}
userdata1={$data}

圖4 Apache原始日誌

圖5 一條Cisco ASA 原始日誌

圖6 Cisco ASA 事件分類

通過過OSSIM歸一化處理後的實際再通過Web前端展現給大家方便閱讀的格式。歸一化處理後的事件和原始日誌的對比方法我們在《開源安全運維平臺OSSIM疑難解析：入門篇》一書中還會講解。而在圖7所示的例子當中，僅使用了Userdata1和Userdata2，並沒有用到Userdata3～Userdata9這些是擴展位，主要是爲了預留給其他設備或服務使用，這裏目標地址會標記成IP地址的形式，例如：Host192.168.11.160。實際上歸一化處理這種操作發生在系統採集和存儲事件之後，關聯和數據分析之前，在SIEM工具中把採集過程中把數據轉換成易讀懂的格式，採用格式化的數據，能更容易理解。

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