[Snort-sigs] SID 1883
anton at ...1177...
Wed Feb 12 20:07:09 EST 2003
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# $Id: snort-sid-template.txt,v 1.1 2002/10/09 13:06:31 cazz Exp $
alert tcp $HTTP_SERVERS $HTTP_PORTS -> $EXTERNAL_NET any (msg:"ATTACK
RESPONSES id check returned nobody"; flow:from_server,established;
content:"uid="; content:"(nobody)"; classtype:bad-unknown; sid:1883;
Summary: A post-compromise behavior indicating the use of a UNIX "id"
Impact: attacker might have gained an ability to execute commands
remotely on the system.
This signature triggers when a UNIX "id" command is used to confirm
the user name of the currently logged in user over any unencrypted
connection. Such connection can be either a legitimate telnet
connection or a result of spawning a shell on FTP, POP3, SMTP or other
port as a consequence of network exploit. The string "uid=" and
"(nobody)" is an output of an "id" command indicating that the user
has "nobody" account privileges, typically used by the web server
process. Seeing such a response indicates that some user connected
over the network to a target web server and likely exploited the web
server to launch a shell.
Attack Scenarios: a buffer overflow exploit against the WWW server
results in "/bin/sh" being executed. An automated script performing an
attack, checks for the success of the exploit via an "id" command.
Ease of Attack: this post-attack behavior can accompany different
False Positives: the signature will trigger if a legitimate system
administrator executes the "id" command over the telnet connection
which uses one of the web ports, as defined in snort.conf
False Negatives: not known
Corrective Action: investigate the server for signs of compromise, run
the integrity checking software, look for other IDS alerts involving
the same IP addresses.
Contributors: Anton Chuvakin <http://www.chuvakin.org>
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