This attack exploits terminal devices that allow themselves to be written
to by other users. The attacker sends command strings to the target terminal
device hoping that the target user will hit enter and thereby execute the
malicious command with their privileges. The attacker can send the results
(such as copying /etc/passwd) to a known directory and collect once the
attack has succeeded.
Attack Prerequisites
User terminals must have a permissive access control such as world
writeable that allows normal users to control data on other user's
terminals.
Typical Likelihood of Exploit
Likelihood: High
Methods of Attack
Injection
Examples-Instances
Description
Any system that allows other peers to write directly to its terminal
process is vulnerable to this type of attack. If the terminals are
available through being overprivileged (i.e. world-writable) or the
attacker is an administrator, then a series of commands in this format
can be used to echo commands out to victim terminals.
"$echo -e "\033[30m\033\132" > /dev/ttyXX
where XX is the tty number of the user under attack. This will paste
the characters to another terminal (tty). Note this technique works only
if the victim's tty is world writable (which it may not be). That is one
reason why programs like write(1) and talk(1) in UNIX systems need to
run setuid." [Hoglund and McGraw 04]
If the victim continues to hit "enter" and execute the commands, there
are an endless supply of vectors available to the attacker, copying
files, open up network connections, ftp out to servers, and so
on.
Attacker Skills or Knowledge Required
Skill or Knowledge Level: Low
Resources Required
Access to a terminal on the target network
Solutions and Mitigations
Design: Ensure that terminals are only writeable by named owner user
and/or administrator
Design: Enforce principle of least privilege
Attack Motivation-Consequences
Privilege Escalation
Information Leakage
Run Arbitrary Code
Injection Vector
Payload delivered through standard user terminal.
Payload
Command(s) executed directly on host, in other victim's terminal
Activation Zone
Multi-user host
Payload Activation Impact
Enables attacker to execute server side code with any commands that the
program owner has privileges to.
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