OSSIM Agent的主要职责是收集网络上存在的各种设备发送的所有数据，然后按照一种标准方式有序发给OSSIM Server，Agent收集到数据后在发送给Server之前要对这些数据进行归一化处理，本文主要就如何有序发送数据与如何完成归一化进行讨论。
OSSIM传感器在通过GET框架实现OSSIM代理和OSSIM服务器之间通信协议和数据格式的之间转换。下面我们先简要看一下ossim-agent脚本：
#!/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()
这里需要GET作为OSSIM代理向OSSIM服务器输送数据。实现紧密整合所需的两个主要操作是“生成”(或)OSSIM兼容事件的“映射Mapping”)和此类数据向OSSIM的“传输”服务器。它负责此类操作的GET框架的两个组件是EventHandler和Sender Agent，如图1所示。
图1 将Get框架内容集成到OSSIM
Event Handler的主要任务是映射数据源插件采集的事件到SIEM实例警报的OSSIM标准化事件格式。为了执行这样的过程，原始消息经历由RAW LOG转换为现有归一化数据字段格式的一个转变;在上图中我们将这些机制表示为“归一化Normalization”和“OSSIM消息”。部分日志归一化代码：
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":
# 以秒为单位
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 + " "
# 返回内部哈希值
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"
]
日志编码代码：
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:
# 失败并添加到缓存
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):
# 从配置文件中获取默认参数
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) 传感器
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) 网络接口
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) 时区
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
# 检测日志的类型
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
#对于一些空属性使用默认值。
event = self._plugin_defaults(event)
# 合并之前检查
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
#在子类中重写
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()
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从上可以看出，传感器的归一化主要负责对每个LOG内数据字段进行重新编码，使其生成一个全新的可能用于发送到OSSIM服务器的完整事件。为达成这种目的GET框架中包含了一些特定的功能，以便将所有的功能转换需要BASE64转换的字段。“OSSIM消息”负责填充GET生成的原始事件中不存在的字段。所以上面讲的plugin_id、plugin_sid是用来表示日志消息来源类型和子类型，这也是生成SIEM事件的必填字段。为事件格式完整性考虑，有些时候在无法确认源或目标IP时，系统默认会采用0.0.0.0来填充该字段。
注意：这种必填字段我们可利用phpmyadmin工具查看OSSIM的MySQL数据库。
Sender Agent负责完成下面两个任务：
发送由GET收集并由事件格式化的事件发送到OSSIM服务器，这项任务由Event Hander创建的消息组成消息队列发送到消息中间件实现，时序图如图2所示。
图2 序列图： 从安全探测器的日志转换到OSSIM服务器事件
2)管理GET框架和OSSIM服务器之间的通信，通信端口为TCP 40001通过双向握手实现。归一化原始日志是规范化过程的一个重要环节，OSSIM在归一化处理日志的同时保留了原始日志，可用于日志归档，提供了一种从规范化事件中提取原始日志的手段。
经过归一化处理的EVENTS，存储到MySQL数据库中，如图3所示。接着就由关联引擎根据规则、优先级、可靠性等参数进行交叉关联分析，得出风险值并发出各种报警提示信息。
图3 OSSIM平台日志存储机制
接下来我们再看个实例，下面是一段Apache、CiscoASA以及SSH的原始日志，如图4、图5、图6所示。
Apache插件中的正则表达式：
[0001 - apache-access] 访问日志
event_type=event
regexp=((?Pd{1,3}.d{1,3}.d{1,3}.d{1,3})(:(?Pd{1,5}))? )?(?PS+) (?PS+) (?PS+) [(?Pd{2}/w{3}/d{4}:d{2}:d{2}:d{2})s+[+-]d{4}] "(?P[^"]*)" (?Pd{3}) ((?Pd+)|-)( "(?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={$id}
[0002 - apache-error] 错误日志
event_type=event
regexp=[(?Pw{3} w{3} d{2} d{2}:d{2}:d{2} d{4})] [(?P(emerg|alert|crit|error|warn|notice|info|debug))] ([client (?PS+)] )?(?P.*)
date={normalize_date($date)}
plugin_sid={translate($type)}
src_ip={resolv($src)}
userdata1={$data}
图4 Apache原始日志