Fail2Ban

Fail2Ban 是一個入侵檢測系統框架,它可以保護電腦伺服器免受蠻力攻擊。以Python程式設計語言編寫,並能夠在類Unix系統上運行,這些系統具有本地安裝的封包控制系統或防火牆的介面,例如Iptables或TCP Wrapper。

Install Fail2Ban on Debian

Installation

Download: https://www.fail2ban.org/wiki/index.php/Downloads

# Debian 7.x
tar xzf 0.9.2.tar.gz
cd fail2ban-0.9.2/
python setup.py install

Verify

fail2ban-client -h
Configuration for Asterisk

On Asterisk)

 /etc/asterisk/logger.conf:

...
[logfiles]
...
fail2ban => notice,warning,security

Restart the logger on Asterisk

asterisk -rx "logger reload"
asterisk -rx "logger show channels"

On Fail2Ban)

/etc/fail2ban/jail.d/asterisk.conf

[asterisk]
enabled = true
logpath = /var/log/asterisk/fail2ban
maxretry = 5
bantime = 259200
Configuration for SSH

/etc/fail2ban/jail.d/sshd.conf

[sshd]
enabled = true
bantime = 7200
findtime = 900
maxretry = 4
Auto startup
cd fail2ban-0.9.2/
cp files/debian-initd /etc/init.d/fail2ban
chmod 0755 /etc/init.d/fail2ban 
update-rc.d fail2ban defaults

Service start

service fail2ban start
Setup Logrotate

/etc/logrotate.d/fail2ban

/var/log/fail2ban.log {
	missingok
	notifempty
	size 30k
	create 0600 root root
	postrotate
		/usr/bin/fail2ban-client set logtarget /var/log/fail2ban.log 1>/dev/null || true
		#/usr/bin/fail2ban-client reload 2> /dev/null || true
	endscript
}
FAQ

Q:以下 Call Log 無法被偵測到

Call from '' (195.154.134.116:5071) to extension '8011441295298642' rejected because extension not found in context 'public'.

Ans:設定 Asterisk 的 allowguest=no

編輯 sip.conf

allowguest=no

Apply the changes

#> asterisk -rx "sip reload"
#> asterisk -rx "sip show settings" | grep -i "Allow unknown access"
  Allow unknown access:   No 

 

Learning Fail2Ban

Fail2ban 是一套以 Python 語言所撰寫的 GPLv2 授權軟體,藉由分析系統紀錄檔,並透過設定過濾條件 (filter) 及動作 (action),當符合我們所設定的過濾條件時,將觸發相對動作來達到自動化反應的效果 (如封鎖來源 IP、寄信通知管理者、查詢來源 IP 資訊等)。因其架構相當彈性,我們可以針對自己的需求,設計不同的過濾條件與動作來達到伺服器防護的功能,或是及時的反應某些異常資訊。常見應用有:

常見的像是 SSH 服務,當使用者嘗試輸入帳號密碼進行登入時,如發生驗證錯誤,系統將紀錄事件於記錄檔中。藉由即時的分析系統紀錄檔,我們可以過濾出一些有用的資訊,再加以判斷此類事件是否對伺服器服務有害。

GitHub: https://github.com/fail2ban/fail2ban

Configuration

Fail2Ban FAQ

Q:服務啟動後出現錯誤

WARNING Determined IP using DNS Lookup:

Ans: 編輯 /etc/fail2ban/jail.conf

usedns = no
Q:[v0.10.0] 啟動後出現錯誤

iptables v1.4.14: unknown option "-w"

Ans:如果你的 iptables 版本不是 v1.4.20 以上,可能發生啟動錯誤,解決方式如下:

新增 /etc/fail2ban/action.d/iptables-common.local

[Init]
lockingopt =
Q:[Asterisk] 以下 Call Log 無法被偵測到

Call from '' (195.154.134.116:5071) to extension '8011441295298642' rejected because extension not found in context 'public'.

Ans:設定 Asterisk 的 allowguest=no

編輯 sip.conf

allowguest=no

套用新設定

#> asterisk -rx "sip reload"
#> asterisk -rx "sip show settings" | grep -i "Allow unknown access"
  Allow unknown access:   No
Q:[Asterisk] 如何驗證一條新規則

Ans: 對於特定的 log 內容,要增加一條新規則,該如何驗證是否有效。

需要過濾的 log 內容:

[2015-01-28 05:40:16] NOTICE[-1] Ext. 9015448702956577: Incoming SIP connection from unknown peer failed for 31.3.244.234 - Unknown connection from peer

在 /etc/fail2ban/filter.d/asterisk.conf 增加一條新規則

NOTICE.* .*: Incoming SIP connection from unknown peer failed for <HOST> - Unknown connection from peer

要驗證此規則是否有效,可以使用以下指令

fail2ban-regex /var/log/asterisk/fail2ban "NOTICE.* .*: Incoming SIP connection from unknown peer failed for <HOST> - Unknown connection from peer"

Tips: fail2ban-regex <path/to/log> <failregex or /etc/fail2ban/filter.s/XXX.conf>

Q:為何沒有 /var/log/fail2ban.log

Ans: 檢查 /etc/fail2ban/fail2ban.conf

#logtarget = SYSLOG
logtarget = /var/log/fail2ban.log

重啟 fail2ban 服務

Q:[Asterisk] 在 Elastix/CentOS 5.3 始終無法 ban IP

使用 fail2ban-client 檢查,明明 log 內有異常連線,但卻無法 ban IP

# fail2ban-client status
Status
|- Number of jail:      1
`- Jail list:           asterisk-iptables

# fail2ban-client status asterisk-iptables
|- filter
|  |- File list:        /var/log/asterisk/fail2ban
|  |- Currently failed: 0
|  `- Total failed:     0
`- action
   |- Currently banned: 0
   |  `- IP list:       
   `- Total banned:     0

解決方法:

編輯 /etc/asterisk/logger.conf

;syslog keyword : This special keyword logs to syslog facility
;將下行註解拿掉
syslog.local0 => notice,warning,error

Reload Asterisk

Q:如何將 IP 從阻擋清單移除
# iptables -D fail2ban-ASTERISK -s 123.123.123.123 -j DROP
或
# iptables -L fail2ban-ASTERISK -nv --line-number
Chain fail2ban-ASTERISK (1 references)
num   pkts bytes target     prot opt in     out     source               destination
1        0     0 DROP       all  --  *      *       134.213.134.172      0.0.0.0/0
2        0     0 DROP       all  --  *      *       46.105.127.222       0.0.0.0/0
3        0     0 DROP       all  --  *      *       116.255.152.101      0.0.0.0/0
4     1364  363K RETURN     all  --  *      *       0.0.0.0/0            0.0.0.0/0

# iptables -D fail2ban-ASTERISK 2     ;刪除第 2 規則
Q:[Asterisk] 如何阻擋不會紀錄來源 IP 的 DDoS 攻擊 Received incoming SIP connection

CLI Log:

Received incoming SIP connection from unknown peer to 003333002972597886748"

以上訊息只有在 sip_general.conf 的 allowguest=yes (by default),才會出現。
此篇也適合解決 Sending fake auth rejection for device 100<sip:100@123.123.123.123> ,這類的攻擊手法。

方法是先 註解 allowguest=no,然後完成下面的步驟。
注意:比較安全的做法應該是將 allowguest=no,然後在 Asterisk 11 以後版本,Log 就可以紀錄到惡意的來源 IP,然後就可以用 Fail2ban 來將其阻擋。

Ans: 編輯 /etc/asterisk/extensions.conf

[from-sip-external]
; 註解原有內容,加上以下內容
exten => _.,1,NoOp(Received incoming SIP connection from unknown peer to ${EXTEN})
exten => _.,n,Set(DID=${IF($["${EXTEN:1:2}"=""]?s:${EXTEN})})
exten => _.,n,Set(foo=${SIPCHANINFO(recvip)})
exten => _.,n,Log(NOTICE,Incoming SIP connection from unknown peer failed for ${foo} - Unknown connection from peer)
exten => _.,n,Hangup
exten => h,1,Hangup
exten => i,1,Hangup
exten => t,1,Hangup 

編輯 /etc/fail2ban/filter.d/asterisk.conf

...
failregex = NOTICE.* .*: Registration from '.*' failed for '<HOST>' - Wrong password
            ...
            ...
            NOTICE.* .*: Incoming SIP connection from unknown peer failed for <HOST> - Unknown connection from peer
Q:[Asterisk] 如何阻擋 Sending fake auth rejection

在 Asterisk 1.11+)

Failed to authenticate device 1005<sip:1005@123.123.123.123>;tag=2071f8ca

在 Asterisk 1.8)

Sending fake auth rejection for device 100<sip:100@123.123.123.123>;tag=99fdd5d7

Ans:不同 Asterisk 版本的解決方法

Asterisk 11)
此版新增一個 Security Log Level 的功能,透過啟用這個,可以記錄攻擊者的來源 IP,然後再透過 fail2ban 去阻擋。

編輯 /etc/fail2ban/filter.d/asterisk.conf

# 加上 SECURITY 那行
failregex = Registration from '.*' failed for '<HOST>:.*' - Wrong password
...
...
            SECURITY.* .*: SecurityEvent="(FailedACL|InvalidAccountID|ChallengeResponseFailed|InvalidPassword)",EventTV="[\d-]+",Severity="[\w]+",Service="[\w]+",EventVersion="\d+",AccountID="\d+",SessionID="0x[\da-f]+",LocalAddress="IPV[46]/(UD|TC)P/[\da-fA-F:.]+/\d+",RemoteAddress="IPV[46]/(UD|TC)P/<HOST>/\d+"(,Challenge="\w+",ReceivedChallenge="\w+")?(,ReceivedHash="[\da-f]+")?$

Asterisk 1.8/1.6)
舊版的 Asterisk 要阻擋這類行為,只能修改原始檔 channels/chan_sip.c,使系統可以記錄攻擊者的來源 IP,修改後必須重新編譯 Asterisk 才能被套用,再設定 fail2abn 去阻擋。

 

Fail2ban Setup

內建白名單

方法一: 編輯 /etc/fail2an/jail.conf

# "ignoreip" can be a list of IP addresses, CIDR masks or DNS hosts. Fail2ban
# will not ban a host which matches an address in this list. Several addresses
# can be defined using space (and/or comma) separator.
ignoreip = 127.0.0.1/8 ::1 192.168.9.0/24 192.168.31.0/24

方法二: 指令 fail2ban-client

# set <JAIL> addignoreip <IP>
# set <JAIL> delignoreip <IP>
fail2ban-client set sshd addignoreip 123.123.123.123
fail2ban-client set sshd delignoreip 123.123.123.123

驗證結果

fail2ban-client get <JAIL> ignoreip
fail2ban-client get asterisk ignoreip
fail2ban-client get sshd ignoreip
黑名單功能客製



fail2ban command

常用指令表
Cmd Description

service fail2ban restart

systemctl restart fail2ban

restart fail2ban service (after edit configuration)
fail2ban-client reload restart fail2ban client
fail2ban-client status get list activated jail
fail2ban-client status <JAIL>
example: fail2ban-client status wplogin
example: fail2ban-client status sshd
get <JAIL> status (the number of unsuccessful attempts and the list of banned IPs)
fail2ban-regex /var/lib/docker/containers/<CONTAINERID>/<CONTAINERID>-json.log /etc/fail2ban/filter.d/wplogin.conf test regex wplogin
fail2ban-regex /var/log/auth.log /etc/fail2ban/filter.d/sshd.conf test regex sshd
fail2ban-regex "line" "failregex" test regex
fail2ban-client set <JAIL-NAME> unbanip <IP-ADDRESS> manually unban IP
fail2ban-client  set <JAIL-NAME> banip <IP-ADDRESS> manually Ban IP
tail -f /var/log/fail2ban.log view fail2ban logs
iptables -L –line-numbers list IP blocked with line numbers
iptables -D <Jail-Name> -s <IP-ADDRESS> -j DROP
Example: Jail-Name =f2b-wplogin
Jail-Name =f2b-sshd
Unban IP
fail2ban-server -b start fail2ban server
docker inspect –format='{{.LogPath}}' $INSTANCE_ID return instance log file path
fail2ban-client get <JAIL-NAME> ignoreip
Test ignoreip for JAIL

Check the version

fail2ban-client version

Check the Help

fail2ban-client -h