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Bug #191

closed

False Negative when matching on negated uricontent.

Added by Will Metcalf over 14 years ago. Updated over 14 years ago.

Status:
Closed
Priority:
Normal
Assignee:
Pablo Rincon
Target version:
1.0.1
Affected Versions:
Effort:
Difficulty:
Label:

Description

The attached signature should fire when processing the attached pcap. It is a bad rule, but it should fire none the less ;-).

alert tcp $HOME_NET any -> $EXTERNAL_NET $HTTP_PORTS (msg:"ET USER_AGENTS Suspicious Mozilla User-Agent - Likely Fake (Mozilla/5.0)"; flow:to_server,established; content:"|0d 0a|User-Agent\: Mozilla/5.0|0d 0a|"; nocase; uricontent:!"|0d 0a|Host\: download.releasenotes.nokia.com"; content:!"Mozilla/5.0|0d 0a|Connection\: Close|0d 0a 0d 0a|"; classtype:trojan-activity; reference:url,doc.emergingthreats.net/2009295; reference:url,www.emergingthreats.net/cgi-bin/cvsweb.cgi/sigs/USER_AGENTS/USER_Agents_Suspicious; sid:2009295; rev:6;)

modifying uricontent:!"|0d 0a|Host\: download.releasenotes.nokia.com"; to be content:!"|0d 0a|Host\: download.releasenotes.nokia.com"; causes the sig to fire but it should fire with uricontent as well.

src/suricata c suricata.yaml -s 2009295.rule -r 2009295.pcap -l ./
...
[686] 28/6/2010 - 13:56:01 - (alert-fastlog.c:255) <Info> (AlertFastLogExitPrintStats) -- (Outputs) Alerts 0
[686] 28/6/2010 -- 13:56:01 - (alert-unified2-alert.c:581) <Info> (Unified2AlertThreadDeinit) -- Alert unified2 module wrote 0 alerts
[686] 28/6/2010 -- 13:56:01 - (log-httplog.c:396) <Info> (LogHttpLogExitPrintStats) -- (Outputs) HTTP requests 1

Files

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2009295.rule (1.05 KB) 2009295.rule fn negated uricontent rule Will Metcalf, 06/28/2010 12:51 PM
2009295.pcap (974 Bytes) 2009295.pcap fn negated uricontent pcap Will Metcalf, 06/28/2010 12:51 PM
0001-Don-t-avoid-inspecting-uricontents-if-we-get-no-matc.patch (3 KB) 0001-Don-t-avoid-inspecting-uricontents-if-we-get-no-matc.patch The problem was that we were skipping the checks of uricontent/urilen and pcre on uris if we got no match on uricontents, but also without checking if they were negated. Now what we do is that we call the inspection with or without mpm matches, but if it Pablo Rincon, 07/02/2010 11:22 AM
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