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Printable Version: RFC1244.PDF
RFC 1244 Site Security Handbook July 1991
snapshot as soon as one suspects that something is wrong. Many
incidents cause a dynamic chain of events to occur, and an initial
system snapshot may do more good in identifying the problem and
any source of attack than most other actions which can be taken at
this stage. Finally, it is important to start a log book.
Recording system events, telephone conversations, time stamps,
etc., can lead to a more rapid and systematic identification of
the problem, and is the basis for subsequent stages of incident
handling.
There are certain indications or "symptoms" of an incident which
deserve special attention:
o System crashes.
o New user accounts (e.g., the account RUMPLESTILTSKIN
has unexplainedly been created), or high activity on
an account that has had virtually no activity for
months.
o New files (usually with novel or strange file names,
such as data.xx or k).
o Accounting discrepancies (e.g., in a UNIX system you
might notice that the accounting file called
/usr/admin/lastlog has shrunk, something that should
make you very suspicious that there may be an
intruder).
o Changes in file lengths or dates (e.g., a user should
be suspicious if he/she observes that the .EXE files in
an MS DOS computer have unexplainedly grown
by over 1800 bytes).
o Attempts to write to system (e.g., a system manager
notices that a privileged user in a VMS system is
attempting to alter RIGHTSLIST.DAT).
o Data modification or deletion (e.g., files start to
disappear).
o Denial of service (e.g., a system manager and all
other users become locked out of a UNIX system, which
has been changed to single user mode).
o Unexplained, poor system performance (e.g., system
response time becomes unusually slow).
o Anomalies (e.g., "GOTCHA" is displayed on a display
terminal or there are frequent unexplained "beeps").
o Suspicious probes (e.g., there are numerous
unsuccessful login attempts from another node).
o Suspicious browsing (e.g., someone becomes a root user
on a UNIX system and accesses file after file in one
user's account, then another's).
None of these indications is absolute "proof" that an incident is
Site Security Policy Handbook Working Group [Page 66]