常見問題

    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 =
    

    重啟服務試試

    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編輯區段

    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編輯區段

    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 從阻擋清單移除編輯區段
    # 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"

    NOTE:

    • 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,詳細資訊可以參考本篇其他章節。

    Ans:

    1. 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 
    

    套用新設定

    asterisk -rx "dialplan reload"
    

    2. 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

    套用新設定

    service fail2ban restart
    
    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

    123.123.123.123 is my external IP of PBX

    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]+")?$
    

     

    教學連結:

    1. http://highsecurity.blogspot.tw/2013...l2ban-088.html
    2. http://issues.freepbx.org/browse/FREEPBX-7573

    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。

    教學連結:https://bugs.debian.org/cgi-bin/bugr...cgi?bug=706739

    TIP:

    在舊版的 Asterisk 還有一個方法,不用修改 chan_sip.c 原始檔,詳細資訊請參閱本篇其他章節。

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