[Snort-sigs] SID 1883

Anton Chuvakin anton at ...1177...
Wed Feb 12 20:07:09 EST 2003

# This is a template for submitting snort signature descriptions to
# the snort.org website
# Ensure that your descriptions are your own
# and not the work of others.  References in the rules themselves
# should be used for linking to other's work.
# If you are unsure of some part of a rule, use that as a commentary
# and someone else perhaps will be able to fix it.
# $Id: snort-sid-template.txt,v 1.1 2002/10/09 13:06:31 cazz Exp $


RESPONSES id check returned nobody"; flow:from_server,established;
content:"uid="; content:"(nobody)"; classtype:bad-unknown; sid:1883;

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.

Detailed Information:

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>

Additional References:

More information about the Snort-sigs mailing list