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OSSEC是一款開源的多平臺的入侵檢測系統(tǒng),可以運(yùn)行于Windows, Linux, OpenBSD/FreeBSD, 以及 MacOS等操作系統(tǒng)中。包括了日志分析,全面檢測,root-kit檢測。

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1. 測試和驗(yàn)證OSSEC泛化及告警規(guī)則
OSSEC默認(rèn)具有一個ossec-logtest工具用于測試OSSEC的泛化及告警規(guī)則。該工具一般默認(rèn)安裝于目錄 /var/ossec/bin 中。
使用示例:
- /var/ossec/bin/ossec-logtest
- 2014/06/1113:15:36 ossec-testrule: INFO: Reading local decoder file.
- 2014/06/11 13:15:36 ossec-testrule: INFO: Started (pid: 26740).
- ossec-testrule: Type one log per line.
- Jun 10 21:29:33 172.16.25.122/172.16.24.32 sshd[24668]: Accepted publickey for root from 172.16.24.121 port 38720 ssh2
- **Phase 1: Completed pre-decoding.
- full event: 'Jun 10 21:29:33 172.16.25.122/172.16.24.32 sshd[24668]: Accepted publickey for root from 172.16.24.121 port 38720 ssh2'
- hostname: '172.16.25.122/172.16.24.32'
- program_name: 'sshd'
- log: 'Accepted publickey for root from 172.16.24.121 port 38720 ssh2'
- **Phase 2: Completed decoding.
- decoder: 'sshd'
- dstuser: 'root'
- srcip: '172.16.24.121'
- **Phase 3: Completed filtering (rules).
- Rule id: '10100'
- Level: '4'
- Description: 'First time user logged in.'
- **Alert to be generated.
如上文所示,當(dāng)輸入日志內(nèi)容:
Jun 1021:29:33 172.16.25.122/172.16.24.32 sshd[24668]: Accepted publickey for rootfrom 172.16.24.121 port 38720 ssh2
該條日志經(jīng)過三步處理,生成了一條4級告警,規(guī)則ID為10100,內(nèi)容為“First time user logged in.”
使用ossec-logtest–v命令,可獲取更詳細(xì)的日志分析邏輯。
- /var/ossec/bin/ossec-logtest -v
- 2014/06/11 13:44:52 ossec-testrule: INFO: Reading local decoder file.
- 2014/06/11 13:44:52 ossec-testrule: INFO: Started (pid: 27091).
- ossec-testrule: Type one log per line.
- Jun 11 21:44:41 172.16.25.122/172.16.24.32 sshd[27743]: Did not receive identification string from 172.16.24.121
- **Phase 1: Completed pre-decoding.
- full event: 'Jun 11 21:44:41 172.16.25.122/172.16.24.32 sshd[27743]: Did not receive identification string from 172.16.24.121'
- hostname: '172.16.25.122/172.16.24.32'
- program_name: 'sshd'
- log: 'Did not receive identification string from 172.16.24.121'
- **Phase 2: Completed decoding.
- decoder: 'sshd'
- srcip: '172.16.24.121'
- **Rule debugging:
- Trying rule: 1 - Generic template for all syslog rules.
- *Rule 1 matched.
- *Trying child rules.
- Trying rule: 5500 - Grouping of the pam_unix rules.
- Trying rule: 5700 - SSHD messages grouped.
- *Rule 5700 matched.
- *Trying child rules.
- Trying rule: 5709 - Useless SSHD message without an user/ip and context.
- Trying rule: 5711 - Useless/Duplicated SSHD message without a user/ip.
- Trying rule: 5721 - System disconnected from sshd.
- Trying rule: 5722 - ssh connection closed.
- Trying rule: 5723 - SSHD key error.
- Trying rule: 5724 - SSHD key error.
- Trying rule: 5725 - Host ungracefully disconnected.
- Trying rule: 5727 - Attempt to start sshd when something already bound to the port.
- Trying rule: 5729 - Debug message.
- Trying rule: 5732 - Possible port forwarding failure.
- Trying rule: 5733 - User entered incorrect password.
- Trying rule: 5734 - sshd could not load one or more host keys.
- Trying rule: 5735 - Failed write due to one host disappearing.
- Trying rule: 5736 - Connection reset or aborted.
- Trying rule: 5707 - OpenSSH challenge-response exploit.
- Trying rule: 5701 - Possible attack on the ssh server (or version gathering).
- Trying rule: 5706 - SSH insecure connection attempt (scan).
- *Rule 5706 matched.
- **Phase 3: Completed filtering (rules).
- Rule id: '5706'
- Level: '6'
- Description: 'SSH insecure connection attempt (scan).'
- **Alert to be generated.
2. 自定義日志泛化規(guī)則
2.1 添加日志源
添加日志源的方式很簡單,通過修改/var/ossec/etc/ossec.conf 即可實(shí)現(xiàn)。
如果日志源是本地文件,可通過添加如下配置實(shí)現(xiàn)。
syslog /path/to/log/file
如果日志源是遠(yuǎn)程syslog,可通過添加如下配置實(shí)現(xiàn)。
syslog udp 2514 172.16.24.0/24
2.2 創(chuàng)建自定義的日志泛化規(guī)則
假如有兩條日志如下文:
Jun 11 22:06:30172.17.153.38/172.16.24.32 /usr/bin/auditServerd[25649]:
User blackrat loginSUCEESS from 172.17.153.36 to 172.17.153.38 distport 3333 .
Jun 11 22:06:30172.17.153.38/172.16.24.32 /usr/bin/auditServerd[25649]:
User blackrat login PWD_ERRORfrom 172.17.153.36 to 172.17.153.38 distport 3333 .
該日志使用ossec-logtest分析之后結(jié)果如下:
Jun 11 22:06:30 172.17.153.38/172.16.24.32 /usr/bin/auditServerd[25649]: User blackrat login SUCEESS from 172.17.153.36 to 172.17.153.38 distport 3333 .
**Phase 1: Completed pre-decoding.
full event: 'Jun 11 22:06:30 172.16.25.130/172.16.24.32 /usr/bin/auditServerd[25649]: User blackrat login SUCEESS from 172.17.153.36 to 172.17.153.38 distport 3333 .'
hostname: '172.17.153.38/172.16.24.32'
program_name: '/usr/bin/auditServerd'
log: 'User blackrat login SUCEESS from 172.17.153.36 to 172.17.153.38 distport 3333 .'**Phase 2: Completed decoding.
No decoder matched
由此可知OSSEC在分析日志的時(shí)候,經(jīng)過了兩個泛化過程:pre-decoding和 decoding。
pre-decoding過程是ossec內(nèi)置的,只要是標(biāo)準(zhǔn)的syslog日志,都可以解析出如下4個基本信息。
Timestamp:Jun 11 22:06:30
Hostname: 172.17.153.38/172.16.24.32
Programe_name: /usr/bin/auditServerd
Log: User blackrat login SUCEESS from 172.17.153.36 to 172.17.153.38 distport 3333.
在decoding過程,用戶可以通過修改/var/ossec/etc/decoder.xml,實(shí)現(xiàn)自定義的泛化。例如在該文件中添加如下規(guī)則:
/usr/bin/auditServerd
再次執(zhí)行/var/ossec/bin/ossec-logtest
- **Phase 1: Completed pre-decoding.
- full event: 'Jun 11 22:06:30 172.17.153.38/172.16.24.32 /usr/bin/auditServerd[25649]: User blackrat login SUCEESS from 172.17.153.36 to 172.17.153.38 distport 3333 .'
- hostname: '172.17.153.38/172.16.24.32'
- program_name: '/usr/bin/auditServerd'
- log: 'User blackrat login SUCEESS from 172.17.153.36 to 172.17.153.38 distport 3333 .'
- **Phase 2: Completed decoding.
- decoder: 'auditServerd'
發(fā)現(xiàn),該條日志成功命中了名為auditServerd的規(guī)則,該條規(guī)則可以準(zhǔn)確的將日志定位為是程序auditServerd所發(fā)出的。
除此之外,基于auditServerd這條規(guī)則,我們還可以添加更多的子規(guī)則,來識別出更多的信息。如:
/usr/bin/auditServerd auditServerd ^User (\S+) login (\S+) from (\S+) to (\S+) distport (\S+) \.$ user,status,srcip,dstip,dstport
再次執(zhí)行/var/ossec/bin/ossec-logtest,可獲取更多的信息,如下:
- **Phase 1: Completed pre-decoding.
- full event: 'Jun 11 22:06:30 172.17.153.38/172.16.24.32/usr/bin/auditServerd[25649]: User blackrat login SUCEESS from 172.17.153.36 to172.17.153.38 distport 3333 .'
- hostname: '172.17.153.38/172.16.24.32'
- program_name: '/usr/bin/auditServerd'
- log: 'User blackrat login SUCEESS from 172.17.153.36 to 172.17.153.38distport 3333 .'
- **Phase 2: Completed decoding.
- decoder: 'auditServerd'
- dstuser: 'blackrat'
- status:'SUCEESS'
- srcip: '172.17.153.36'
- dstip: '172.17.153.
用戶通過配置上述正則表達(dá)式,獲取特定字段,用于后續(xù)的關(guān)聯(lián)分析。OSSEC一共內(nèi)置了14個用戶可解析的字段:
- location – where the log came from (only on FTS)
- srcuser - extracts the source username
- dstuser - extracts the destination (target) username
- user – an alias to dstuser (only one of the two can be used)
- srcip - source ip
- dstip - dst ip
- srcport - source port
- dstport - destination port
- protocol – protocol
- id – event id
- url - url of the event
- action – event action (deny, drop, accept, etc)
- status – event status (success, failure, etc)
- extra_data – Any extra data
3. 自定義日志告警規(guī)則
3.1 規(guī)則文件路徑配置
OSSEC的規(guī)則配置文件默認(rèn)路徑為/var/ossec/rules/,要加載規(guī)則文件,需要在/var/ossec/etc/ossec.conf 中配置,默認(rèn)的配置如下:
rules_config.xml pam_rules.xml sshd_rules.xml telnetd_rules.xml syslog_rules.xml arpwatch_rules.xml - ......
clam_av_rules.xml bro-ids_rules.xml dropbear_rules.xml local_rules.xml
其實(shí)通過下列配置,可以實(shí)現(xiàn)加載/var/ossec/rules 下的所有規(guī)則文件:
rules
于泛化規(guī)則,也可以通過配置decoder_dir域來實(shí)現(xiàn),如:
rules/plugins/decoders
上述配置可將/var/ossec/rules/plugins/plugins/decoders目錄下所有的xml文件都添加為OSSEC日志泛化規(guī)則。
對于更詳細(xì)的配置及語法,可參考下列文檔:
http://ossec-docs.readthedocs.org/en/latest/syntax/head_ossec_config.rules.html#element-rule_dir
3.2 OSSEC告警規(guī)則配置
例如,我們需要增加對程序auditServerd的告警規(guī)則,我們需要針對auditServerd程序新建一個規(guī)則文件,對于OSSEC中已經(jīng)存在的規(guī)則文件如sshd, openbsd, vsftpd等,我們只需要在對應(yīng)的文件中進(jìn)行新增或修改。
首先我們新建文件
/var/ossec/rules/auditServerd_rules.xml
添加如下內(nèi)容:
auditServerd Grouping for the auditServerd rules. 80000 blackrat 172.17.153.36 User blackrat is not allowed login from 172.17.153.36!
上述規(guī)則中,規(guī)則id 80000 用于對日志進(jìn)行分組計(jì)數(shù),假如日志中出現(xiàn)了泛化為auditServerd的日志,則對該日志分組為auditServer,且狀態(tài)機(jī)計(jì)數(shù)加1.
規(guī)則80001描述了假如user為blackrat,srcip為172.17.153.36 則命中,并發(fā)出“User blackrat is not allowed login from 172.17.153.36!”的告警。
將該文件路徑加入到文件/var/ossec/etc/ossec.conf中
- …
dropbear_rules.xml local_rules.xml auditServerd_rules.xml
執(zhí)行/var/ossec/bin/ossec-logtest,結(jié)果如下:
- **Phase 1: Completed pre-decoding.
- full event: 'Jun 11 22:06:30 172.17.153.38/172.16.24.32 /usr/bin/auditServerd[25649]: User blackrat login SUCEESS from 172.17.153.36 to 172.17.153.38 distport 3333 .'
- hostname: '172.17.153.38/172.16.24.32'
- program_name: '/usr/bin/auditServerd'
- log: 'User blackrat login SUCEESS from 172.17.153.36 to 172.17.153.38 distport 3333 .'
- **Phase 2: Completed decoding.
- decoder: 'auditServerd'
- dstuser: 'blackrat'
- status: 'SUCEESS'
- srcip: '172.17.153.36'
- dstip: '172.17.153.38'
- dstport: '3333'
- **Phase 3: Completed filtering (rules).
- Rule id: '80001'
- Level: '10'
- Description: 'User blackrat is not allowed login from 172.17.153.36!'
- **Alert to be generated.
3.3 關(guān)聯(lián)分析告警規(guī)則
OSSEC可以實(shí)現(xiàn)基于因果關(guān)系、事件頻次的關(guān)聯(lián)分析告警,具體實(shí)現(xiàn)方式如下。
假如我們想要實(shí)現(xiàn)當(dāng)來自同一IP的用戶登陸auditServerd,在1分鐘內(nèi)達(dá)到5次登錄失敗時(shí),進(jìn)行告警,我們可以配置規(guī)則如下:
auditServerd Grouping for the auditServerd rules. 80000 SUCEESS blackrat 172.17.153.36 User blackrat is not allowed login from 172.17.153.36! 80000 PWD_ERROR authServer_login_failures, login auditServerd password error. authServer_login_failures auditServerd brute force trying to get access to the audit system. authentication_failures,
執(zhí)行/var/ossec/bin/ossec-logtest,連續(xù)五次輸入日志:
結(jié)果如下:
- **Phase 1: Completed pre-decoding.
- full event: 'Jun 11 22:06:30 172.17.153.38/172.16.24.32 /usr/bin/auditServerd[25649]: User blackrat login PWD_ERROR from 172.17.153.36 to 172.17.153.38 distport 3333 .'
- hostname: '172.17.153.38/172.16.24.32'
- program_name: '/usr/bin/auditServerd'
- log: 'User blackrat login PWD_ERROR from 172.17.153.36 to 172.17.153.38 distport 3333 .'
- **Phase 2: Completed decoding.
- decoder: 'auditServerd'
- dstuser: 'blackrat'
- status: 'PWD_ERROR'
- srcip: '172.17.153.36'
- dstip: '172.17.153.38'
- dstport: '3333'
- **Phase 3: Completed filtering (rules).
- Rule id: '80003'
- Level: '15'
- Description: 'auditServerd brute force trying to get access to the audit system.'
- **Alert to be generated.
對于OSSEC日志告警規(guī)則更詳細(xì)的語法,參見:
http://ossec-docs.readthedocs.org/en/latest/syntax/head_rules.html
對于OSSEC中正則表達(dá)式的語法,參加:
http://ossec-docs.readthedocs.org/en/latest/syntax/regex.html
標(biāo)題名稱:OSSEC日志泛化及告警規(guī)則配置
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