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Network Security Snort-Signatures
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[Snort-sigs] False positives on FTP command 100 character limit

Subject: [Snort-sigs] False positives on FTP command 100 character limit
Date: Thu, 2 Sep 2004 23:49:42 +0200
Hi,

I'm getting a lot of false positives on the FTP command size checks, like rule 1748. They are (mostly) caused FTP clients that retrieve a file using the complete path in the RETR command. Is there a reason the limit is at 100 characters, or is it safe to raise that limit to reduce the number of false positives?

Rule 2546 is triggered a lot by the WS-FTP Pro synchronisation tool. It is a tool to synchronise a local directory with a directory on an FTP server. It uses a lot of MDTM commands with the full pathname to compare the local and remote files.

Examples:

length = 109

000 : 4D 44 54 4D 20 32 30 30 34 30 36 32 35 31 38 33   MDTM 20040625183
010 : 33 34 34 20 2F 77 65 62 73 69 74 65 2F 70 65 72   344 /website/per
020 : 73 6F 6E 65 65 6C 2F 70 65 72 73 6F 6E 65 65 6C   soneel/personeel
030 : 73 76 65 72 65 6E 69 67 69 6E 67 2F 66 6F 74 6F   svereniging/foto
040 : 27 73 20 32 35 20 6A 75 6E 69 20 32 30 30 34 2F   's 25 juni 2004/
050 : 44 61 67 6A 65 20 75 69 74 20 70 76 20 32 35 30   Dagje uit pv 250
060 : 36 30 34 20 30 34 39 2E 6A 70 67 0D 0A            604 049.jpg..

length = 130

000 : 4D 44 54 4D 20 32 30 30 31 30 35 31 31 31 30 32   MDTM 20010511102
010 : 30 30 34 20 2F 77 65 62 73 69 74 65 2F 69 6E 68   004 /website/inh
020 : 6F 75 64 2F 6C 65 65 72 6C 69 6E 67 65 6E 7A 6F   oud/leerlingenzo
030 : 72 67 2F 68 61 6E 73 20 76 65 72 62 72 75 67 67   rg/hans verbrugg
040 : 65 6E 2F 69 6E 66 6F 72 6D 61 74 69 65 20 6D 61   en/informatie ma
050 : 74 65 72 69 61 61 6C 2F 76 6F 6F 72 6C 69 63 68   teriaal/voorlich
060 : 74 69 6E 67 20 68 61 6E 73 2F 76 69 73 75 65 6C   ting hans/visuel
070 : 65 20 77 61 61 72 6E 65 6D 69 6E 67 2E 64 6F 63   e waarneming.doc
080 : 0D 0A                                             ..

Thanks,
Sander Steffann.



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