ElastAlert监控日志告警Web攻击行为

2018-01-20 483400人围观 ,发现 5 个不明物体 WEB安全

*本文作者:shystartree,本文属 FreeBuf 原创奖励计划,未经许可禁止转载。

由于公司需要监控web攻击行为,而因某些原因搭不了waf,才不得不用ElastAlert进行告警,此为前提。

一、ELK安装

Elasticsearch 是一个分布式、可扩展、实时的搜索与数据分析引擎。 它能从项目一开始就赋予你的数据以搜索、分析和探索的能力。

Logstash是一款轻量级的日志搜集处理框架,可以方便的把分散的、多样化的日志搜集起来,并进行自定义的处理,然后传输到指定的位置,

Kibana是一个开源的分析与可视化平台,设计出来用于和Elasticsearch一起使用的。你可以用kibana搜索、查看、交互存放在Elasticsearch索引里的数据,使用各种不同的图表、表格、地图等kibana能够很轻易地展示高级数据分析与可视化。

ELK这一套软件可以当作一个MVC模型,logstash是controller层,Elasticsearch是一个model层,kibana是view层。首先将数据传给logstash,它将数据进行过滤和格式化(转成JSON格式),然后传给Elasticsearch进行存储、建搜索的索引,kibana提供前端的页面再进行搜索和图表可视化,它是调用Elasticsearch的接口返回的数据进行可视化。logstash和Elasticsearch是用Java写的,kibana使用node.js框架。

安装方法网上有好多,此处就不再阐述。在试用了几乎所有的安装方法后,介绍下本人觉得比较快捷有效的安装方法:

1.1 下载安装匹配版本的elk

elastalert目前还不支持elk6.0以上版本,本人就是因为版本问题而折腾了好久,所以在安装elk的时候需要特别注意版本问题。

我的服务器概况:
Distributor ID:   Ubuntu
Description:  Ubuntu 16.04.1 LTS
Release:  16.04
Codename: xenial

在尝试了众多安装方法后,还是发现在官方网站下载deb包直接安装最为有效便捷。 (系统若为centos,下载对应的rpm包)

搜索版本下载

Elasticsearch:5.5.2
Kibana:5.5.2
Logstash:6.0.0
filebeat:6.0.0 (轻量级的logstash,这个下载tar包)

​ 理论上,Elasticsearch及Kibana版本为5.x都可以,而Logstash与elastalert没啥联系,所以Logstash(大于或等于Elasticsearch及Kibana的5.x版本)能向Elasticsearch传递日志信息即可。

下载完elk的deb包后,使用dpkg -i命令很快就能顺利安装。

1.2 elk配置

​ 同样,此处也只介绍本人的简单配置。我这里是只让Logstash对外开放负责收集日志,而Elasticsearch及Kibana仅在内网访问,故Elasticsearch及Kibana并未开启账户认证登陆,有需要开启或其他需求的读者们请自行搜索。

/etc/elasticsearch/elasticsearch.yml:
# Set the bind address to a specific IP (IPv4 or IPv6):
#
network.host: 127.0.0.1
#
# Set a custom port for HTTP:
#
http.port: 9200
/etc/kibana/kibana.yml:
 Kibana is served by a back end server. This setting specifies the port to use.
  server.port: 5601

  # Specifies the address to which the Kibana server will bind. IP addresses and host names are both valid values.
  # The default is 'localhost', which usually means remote machines will not be able to connect.
  # To allow connections from remote users, set this parameter to a non-loopback address.
  server.host: "localhost"

  # The URL of the Elasticsearch instance to use for all your queries.
  elasticsearch.url: "http://localhost:9200"

我这里需要用到自定义的配置文件,故配置文件是自行创建的,放在/usr/share/logstash/bin中,取名为filebeat_log.conf : 

  input {
  beats {
  port => 5044
  client_inactivity_timeout => 90
  codec => json
      }

  }

  filter {
    date {
      match => [ "timestamp", "dd/MMM/yyyy:HH:mm:ss Z" ]
      target => ["datetime"]
    }
    geoip {
      source => "remote_addr"
    }

    mutate {
  remove_field => ["tags", "beat"]
    }
  }

  output {
  elasticsearch {
  hosts => "localhost:9200"
  index => "logstash-%{+YYYY.MM.dd}"
  }
  stdout {
  codec => rubydebug
  }
  

 1.3 启动方法

elasticsearch&kibana启动

扫描新的单元&重新载入systemd:

systemctl daemon-reload

加入开机自启动:

systemctl enable elasticsearch.service

systemctl enable kibana.service

启动:

systemctl start elasticsearch

systemctl start kibana

查看状态:

systemctl status elasticsearch

systemctl status kibana

logstash启动

进入/usr/share/logstash/bin:

nohup ./logstash -f filebeat_log.conf> /dev/null 2>&1 &

二、使用filebeat进行分布式收集

一开始直接使用logstash进行日志收集,发现资源消耗实在太大,无奈寻找解决方法,发现filebeat是一个轻量级的日志传输工具,故使用filebeat作为日志收集,而logstash作为中心过滤器向es传递日志。

所以整体的架构如:   

* A、B、C、D…(这些服务器是准备监控被攻击行为,装上filebeat)
* 主服务器(装上elk和elastalert,负责收集过滤分析filebeat传递的日志和告警)

下面以tomcat为例子,分享我的配置文件filebeat.yml(nginx的话,修改paths的路径):

  filebeat.prospectors:

  # Each - is a prospector. Most options can be set at the prospector level, so
  # you can use different prospectors for various configurations.
  # Below are the prospector specific configurations.

  - type: log

    # Change to true to enable this prospector configuration.
    enabled: true

    # Paths that should be crawled and fetched. Glob based paths.
    paths:
      - /home/qy/apache-tomcat-9.0.1/logs/localhost_access_log.*.txt
      #- c:\programdata\elasticsearch\logs\*
    # Exclude lines. A list of regular expressions to match. It drops the lines that are
    # matching any regular expression from the list.
    #exclude_lines: ['^DBG']
    document_type: tomcat-log
    scan_frequency: 15s
    ignore_older: 20m
    close_inactive: 12m
    clean_inactive: 30m
    close_removed: true
    clean_removed: true
    ....
    #----------------------------- Logstash output --------------------------------

  output.logstash:
    # The Logstash hosts
    hosts: ["188.88.88.88:5044"]

直接解压下载的tar包,进入目录修改配置文件。然后启动filebeat:nohup ./filebeat -e -c filebeat.yml >/dev/null 2>&1 &

三、日志格式转json​

 为方便kibana分析和elastalert的取值,日志的格式要为json格式,上述的logstash配置文件已适配json格式。

公司的应用服务器中均为nginx和tomcat,故本文只介绍tomcat及nginx的json格式配置方法,其他服务器配置方法请自行搜索。

3.1 tomcat的json格式配置

​ 打开config/server.xml,在最后的位置修改log的输出配置为:

    <Valve className="org.apache.catalina.valves.AccessLogValve" directory="logs"
                 prefix="localhost_access_log" suffix=".txt" pattern="{&quot;time&quot;:&quot;%t&quot;,&quot;remote_addr&quot;:&quot;%h&quot;,&quot;remote_user&quot;:&quot;%l&quot;,&quot;request&quot;:&quot;%r&quot;,&quot;status&quot;:&quot;%s&quot;,&quot;body_bytes_sent&quot;:&quot;%b&quot;,&quot;http_referer&quot;:&quot;%{Referer}i&quot;,&quot;http_user_agent&quot;:&quot;%{User-Agent}i&quot;,&quot;http_x_forwarded_for&quot;:&quot; %{X-Forwarded-For}i&quot;,&quot;request_time&quot;:&quot;%T&quot;,&quot;host&quot;:&quot;%v&quot;,&quot;port&quot;:&quot;%p&quot;}"/>

​ 然后重启tomcat,即生效。

3.2 nginx的json格式配置

进入`/etc/nginx`打`nginx.conf`,加入如下配置:
  http {

          ##
          # Basic Settings
          ##

          sendfile on;
          tcp_nopush on;
          tcp_nodelay on;
          keepalive_timeout 65;
          types_hash_max_size 2048;
          # server_tokens off;

          log_format logstash_json '{"time": "$time_local", '
         '"remote_addr": "$remote_addr", '
         '"remote_user": "$remote_user", '
         '"request": "$request", '
         '"status": "$status", '
         '"body_bytes_sent": "$body_bytes_sent", '
         '"http_referer": "$http_referer", '
         '"http_user_agent": "$http_user_agent", '
         '"http_x_forwarded_for": "$http_x_forwarded_for", '
         '"request_time": "$request_time", '
         '"request_length": "$request_length", '
         '"host": "$http_host"}';
       }


最后nginx -s reload即可

四、使用elastalert进行告警

​ 在经过上述的安装及配置后,终于轮到我们的主角–ElastAlert出来了,其他的告警工具还有411 Alert ManagementElasticsearch watch ,请读者们自行确定需要使用哪个。

ElastAlert使用python编写,具有容易上手、文档全等特点,虽然这个工具拥有如此多的优点,在搭建过程还是遇到了很多很多的未知错误,主要原因是网上的资料大多是针对es5.x以前的版本而没什么现成的资料可供参考。

4.1 安装elastalert

  git clone https://github.com/Yelp/elastalert.git 
  cd elastalert
  python setup.py install            //可能需要sudo
  Pip install -r requirements.txt    //可能需要sudo
  cp config.yaml.example config.yaml

​ 具体的功能本文就不一一介绍了,请自行前往官方文档了解

4.2 创建索引

​ 安装完成后会系统中会自带三个命令:

​  elastalert-create-indexelastalert-rule-from-kibana 、elastalert-test-rule

​ 使用elastalert-create-index,根据提示设置es后按回车默认即可。
​ 配置完索引及配置文件后,可以使用elastalert-test-rule进行测试。这里有个bug,如果出现TransportError(400, u'search_phase_execution_exception', u'No mapping found for [alert_time] in order to sort on')之类的错误,在确认没有其他的问题时,可以先删除索引curl -XDELETE http://localhost:9200/*,再使用elastalert-create-index重新生成索引。

4.3 配置config.yaml

  rules_folder: example_rules

  # How often ElastAlert will query Elasticsearch
  # The unit can be anything from weeks to seconds
  run_every:
    seconds: 3   #每三秒向es请求数据
  # ElastAlert will buffer results from the most recent
  # period of time, in case some log sources are not in real time
  buffer_time:
    minutes: 15  
    #日志会延迟进入es,这里是配置query的向前的时间范围,这是15分钟,即查询 time[now-15m, now]

  # The Elasticsearch hostname for metadata writeback
  # Note that every rule can have its own Elasticsearch host
  es_host: 188.88.88.88

  # The Elasticsearch port
  es_port: 9200

  # Optional URL prefix for Elasticsearch
  #es_url_prefix: elasticsearch

  # Connect with TLS to Elasticsearch
  #use_ssl: True

  # Verify TLS certificates
  #verify_certs: True

  # GET request with body is the default option for Elasticsearch.
  # If it fails for some reason, you can pass 'GET', 'POST' or 'source'.
  # See http://elasticsearch-py.readthedocs.io/en/master/connection.html?highlight=send_get_body_as#transport
  # for details
  #es_send_get_body_as: GET

  # Option basic-auth username and password for Elasticsearch
  #es_username: someusername
  #es_password: somepassword

  # The index on es_host which is used for metadata storage
  # This can be a unmapped index, but it is recommended that you run
  # elastalert-create-index to set a mapping
  writeback_index: elastalert_status

  # If an alert fails for some reason, ElastAlert will retry
  # sending the alert until this time period has elapsed
  alert_time_limit:
    days: 1

以上各字段的解释:

Rules_folder:用来加载下一阶段rule的设置,默认是example_rules

Run_every:用来设置定时向elasticsearch发送请求

Buffer_time:用来设置请求里时间字段的范围,默认是45分钟

Es_host:elasticsearch的host地址

Es_port:elasticsearch 对应的端口号

Use_ssl:可选的,选择是否用SSL连接es,true或者false

Verify_certs:可选的,是否验证TLS证书,设置为true或者false,默认为- true

Es_username:es认证的username

Es_password:es认证的password

Es_url_prefix:可选的,es的url前缀(我的理解是https或者http)

Es_send_get_body_as:可选的,查询es的方式,默认的是GET

Writeback_index:elastalert产生的日志在elasticsearch中的创建的索引

Alert_time_limit:失败重试的时间限制

4.4 告警配置介绍

​ 在example_rules目录中新建yaml配置文件 webattack_frequency.yaml,下面分开介绍这个配置文件的内容(下个小节将分享我的配置文件,此小节仅解释其中的必要设置项): 

1、告警规则

ElastAlert支持11种告警规则,本文不一一介绍了,为响应web攻击行为,本文选用的告警规则是frequency。 

name: web attack

# (Required)
# Type of alert.
# the frequency rule type alerts when num_events events occur with timeframe time
type: frequency

# (Required, frequency specific)
# Alert when this many documents matching the query occur within a timeframe
num_events: 10

# (Required, frequency specific)
# num_events must occur within this amount of time to trigger an alert
timeframe:
  minutes: 1
  
# (Required)
# Index to search, wildcard supported
index: logstash-*      #对应logstash的配置文件中output的elasticsearch index前缀

filter:
- query_string:
# sql insert  xss detect
        query: "request: select.+(from|limit) OR request: union(.*?)select OR request: into.+(dump|out)file "

上述配置文件的意图即是:在一分钟内将匹配query里面的sql注入规则,若匹配次数达到10次,即进行报警。

2、使用邮箱进行告警

ElastAlert提供了 10 多种通知的类型,本文选用的是邮箱告警,还有微信告警钉钉告警,若有需要,请自行配置。

smtp_host: smtp.qiye.163.com
smtp_port: 25

smtp_auth_file: /Users/qy/Downloads/work/elastalert/example_rules/smtp_auth_file.yaml
#回复给那个邮箱
email_reply_to: xxx@163.com
#从哪个邮箱发送
from_addr: xxx@163.com



# (Required)
# The alert is use when a match is found
alert:
- "email"

# (required, email specific)
# a list of email addresses to send alerts to
email:
- "shystartree@163.com"

alert_subject: "web attack may be by {} at @{}"
alert_subject_args:
  - remote_addr
  - time

alert_text_type: alert_text_only

alert_text: |
  你好,服务器({})可能正在受到web攻击,请采取手段阻止!!!!
  ### 截止发邮件前匹配到的请求数:{}
  > 发生时间: {}
  > timestamp:{}
  > attacker's ip: {}
  > request: {}
  > status:{}
  > UA头:{}
  >>> 参考来源:{}

alert_text_args:
  - host
  - num_hits
  - time
  - "@timestamp"
  - remote_addr
  - request
  - status
  - http_user_agent
  - source

smtp_auth_file.yaml的配置内容会在下个小节给出,在这个配置中,我自定义了 alert 的内容,更为精确地突出了攻击者ip、受攻击的服务器、攻击事件等信息。

3、减少重复告警的频率

在实际的使用中,若使用上述的配置,受到攻击的时候邮箱将不断地收到邮件,而这些邮件都对应着同一个攻击实例,根本没必要重复收取,于是,我使用了如下的配置:

   # 用来区分报警,跟 realert 配合使用,在这里意味着,
   # 5 分钟内如果有重复报警,那么当 name 不同时,会当做不同的报警处理,可以是数组
   query_key:
     - name

   # 5 分钟内相同的报警不会重复发送
   realert:
     minutes: 5

   # 指数级扩大 realert 时间,中间如果有报警,
   # 则按照 5 -> 10 -> 20 -> 40 -> 60 不断增大报警时间到制定的最大时间,
   # 如果之后报警减少,则会慢慢恢复原始 realert 时间
   exponential_realert:
     hours: 1

在本人实际测试的攻击场景中,发现使用了exponential_realert后,会错过很多告警(这些告警并不是同一个攻击实例),暂时不确定原因,还请读者们自行确定是否开启该设置。

4.5webattack_frequency.yamlsmtp_auth_file.yaml配置文件内容

上述的4.4小节中对每个配置都作了简单的介绍,这里就直接放出web攻击预警的配置文件供各位读者参考。

webattack_frequency.yaml:

# Alert when the rate of events exceeds a threshold

# (Optional)
# Elasticsearch host
#es_host: 188.88.88.88

# (Optional)
# Elasticsearch port
#es_port: 9200

# (OptionaL) Connect with SSL to Elasticsearch
#use_ssl: True

# (Optional) basic-auth username and password for Elasticsearch
#es_username: someusername
#es_password: somepassword

# (Required)
# Rule name, must be unique
name: web attack

realert:
  minutes: 5

# (Required)
# Type of alert.
# the frequency rule type alerts when num_events events occur with timeframe time
type: frequency

# (Required)
# Index to search, wildcard supported
index: logstash-*

# (Required, frequency specific)
# Alert when this many documents matching the query occur within a timeframe
num_events: 10

# (Required, frequency specific)
# num_events must occur within this amount of time to trigger an alert
timeframe:
  #hours: 4
  minutes: 1

# (Required)
# A list of Elasticsearch filters used for find events
# These filters are joined with AND and nested in a filtered query
# For more info: http://www.elasticsearch.org/guide/en/elasticsearch/reference/current/query-dsl.html
#filter:
#- term:
#    some_field: "some_value"

filter:
- query_string:
# sql insert  xss detect
        query: "request: select.+(from|limit) OR request: union(.*?)select OR request: into.+(dump|out)file OR

        request: (base64_decode|sleep|benchmark|and.+1=1|and.+1=2|or%20|exec|information_schema|where%20|union%20|%2ctable_name%20|cmdshell|table_schema) OR

        request: (iframe|script|body|img|layer|div|meta|style|base|object|input|onmouseover|onerror|onload) OR

        request: .+etc.+passwd OR http_user_agent:(HTTrack|harvest|audit|dirbuster|pangolin|nmap|sqln|-scan|hydra|Parser|libwww|BBBike|sqlmap|w3af|owasp|Nikto|fimap|havij|PycURL|zmeu|BabyKrokodil|netsparker|httperf|bench) OR

        status: (400|404|500|501)

        NOT (request:_health.html OR remote_addr:222.222.222.222  )
        "


smtp_host: smtp.qiye.163.com
smtp_port: 25

smtp_auth_file: /Users/qy/Downloads/work/elastalert/example_rules/smtp_auth_file.yaml
#回复给那个邮箱
email_reply_to: xxx@163.com
#从哪个邮箱发送
from_addr: xxx@163.com



# (Required)
# The alert is use when a match is found
alert:
- "email"

# (required, email specific)
# a list of email addresses to send alerts to
email:
- "shystartree@163.com"

alert_subject: "web attack may be by {} at @{}"
alert_subject_args:
  - remote_addr
  - time

alert_text_type: alert_text_only

alert_text: |
  你好,服务器({})可能正在受到web攻击,请采取手段阻止!!!!
  ### 截止发邮件前匹配到的请求数:{}
  > 发生时间: {}
  > timestamp:{}
  > attacker's ip: {}
  > request: {}
  > status:{}
  > UA头:{}
  >>> 参考来源:{}

alert_text_args:
  - host
  - num_hits
  - time
  - "@timestamp"
  - remote_addr
  - request
  - status
  - http_user_agent
  - source

smtp_auth_file.yaml:

user: xxx@163.com
password: password

4.6 运行elastalert

在成功配置完ElastAlert后将生成三个配置文件:

config.yaml、webattack_frequency.yaml、smtp_auth_file.yaml

  • 启动elastalert服务,监听elasticsearch:

nohup python -m elastalert.elastalert --verbose --rule webattack_frequency.yaml >/dev/null 2>&1 &

  • 为实现守护进程的作用,可以配合supervisor进行使用,本文不再阐述。

4.7 运行效果:

当匹配到自定义攻击规则的时候,ElastAlert将会以邮件方式发送告警信息:

web attack may be by 104.38.13.21 at @[13/Jan/2018:16:06:58 +0800]
xxx 发给 shystartree   
你好,服务器(199.222.36.31)可能正在受到web攻击,请采取手段阻止!!!!
### 截止发邮件前匹配到的请求数:20
> 发生时间: [13/Jan/2018:16:06:58 +0800]
> timestamp:2018-01-13T08:07:04.930Z
> attacker's ip: 184.233.9.121
> request: GET /dbadmin/scripts/setup.php HTTP/1.0
> status:200
> UA头:ZmEu
>>> 参考来源:/log/localhost_access_log.2018-01-13.txt

五、总结

ElastAlert除了本文介绍的告警web攻击行为外,还能进行异常告警等。使用了frequency的规则后,基本能达到识别web攻击的目的。在实际的使用中,elastalert能稳定运行,且能根据自定义配置文件精确告警,缺点是告警的格式不够美观和需要频繁地修改配置文件。

参考链接:

ElastAlert:『Hi,咱服务挂了』:https://xizhibei.github.io/2017/11/19/alerting-with-elastalert/
[ElastAlert]介绍和安装:https://segmentfault.com/a/1190000008227486
被elastalert虐了:http://blog.csdn.net/vbaspdelphi/article/details/54291066

*本文作者:shystartree,本文属 FreeBuf 原创奖励计划,未经许可禁止转载。

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