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FTP / Telnet normalization and anomaly detection
From: "Frank Kirschner" <frank () celebrate de>
Date: Fri, 6 Dec 2013 16:17:33 +0100

Hello snort-users,
 
the FileZilla FTP client uses the "MFMT" command during a FTP session. Snort
blocks this host because "MFMT" is an unknown command.
I have add "MFMT" in my snort.conf as followed:

# FTP / Telnet normalization and anomaly detection.  For more information,
see README.ftptelnet
preprocessor ftp_telnet: global inspection_type stateful encrypted_traffic
no check_encrypted
preprocessor ftp_telnet_protocol: telnet \
    ayt_attack_thresh 20 \
    normalize ports { 23 } \
    detect_anomalies
preprocessor ftp_telnet_protocol: ftp server default \
    def_max_param_len 100 \
    ports { 21 2100 3535 } \
    telnet_cmds yes \
    ignore_telnet_erase_cmds yes \
    ftp_cmds { ABOR ACCT ADAT ALLO APPE AUTH CCC CDUP } \
    ftp_cmds { CEL CLNT CMD CONF CWD DELE ENC EPRT } \
    ftp_cmds { EPSV ESTA ESTP FEAT HELP LANG LIST LPRT } \
    ftp_cmds { LPSV MACB MAIL MDTM MIC MKD MLSD MLST } \
    ftp_cmds { MODE NLST NOOP OPTS PASS PASV PBSZ PORT } \
    ftp_cmds { PROT PWD QUIT REIN REST RETR RMD RNFR } \
    ftp_cmds { RNTO SDUP SITE SIZE SMNT STAT STOR STOU } \
    ftp_cmds { STRU SYST TEST TYPE USER XCUP XCRC XCWD } \
    ftp_cmds { XMAS XMD5 XMKD XPWD XRCP XRMD XRSQ XSEM } \
    ftp_cmds { XSEN XSHA1 XSHA256 MFMT } \
    alt_max_param_len 0 { ABOR CCC CDUP ESTA FEAT LPSV NOOP PASV PWD QUIT
REIN STOU SYST XCUP XPWD } \
    alt_max_param_len 512 { ALLO APPE CMD HELP NLST RETR RNFR STOR STOU XMKD
} \
    alt_max_param_len 256 { CWD RNTO } \
    alt_max_param_len 400 { PORT } \
    alt_max_param_len 512 { SIZE MFMT } \
    chk_str_fmt { ACCT ADAT ALLO APPE AUTH CEL CLNT CMD } \
    chk_str_fmt { CONF CWD DELE ENC EPRT EPSV ESTP HELP } \
    chk_str_fmt { LANG LIST LPRT MACB MAIL MDTM MIC MKD } \
    chk_str_fmt { MLSD MLST MODE NLST OPTS PASS PBSZ PORT } \
    chk_str_fmt { PROT REST RETR RMD RNFR RNTO SDUP SITE } \
    chk_str_fmt { SIZE SMNT STAT STOR STRU TEST TYPE USER } \
    chk_str_fmt { XCRC XCWD XMAS XMD5 XMKD XRCP XRMD XRSQ } \ 
    chk_str_fmt { XSEM XSEN XSHA1 XSHA256 MFMT } \
    cmd_validity ALLO < int [ char R int ] > \    
    cmd_validity EPSV < [ { char 12 | char A char L char L } ] > \
    cmd_validity MACB < string > \
    cmd_validity MDTM < [ date nnnnnnnnnnnnnn[.n[n[n]]] ] string > \
    cmd_validity MODE < char ASBCZ > \
    cmd_validity PORT < host_port > \
    cmd_validity PROT < char CSEP > \
    cmd_validity STRU < char FRPO [ string ] > \    
    cmd_validity TYPE < { char AE [ char NTC ] | char I | char L [ number ]
} >
preprocessor ftp_telnet_protocol: ftp client default \
    max_resp_len 256 \
    bounce yes \
    ignore_telnet_erase_cmds yes \
    telnet_cmds yes

Now I have the result, some clients are blocked and some not. But why?

best regards
Frank


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