Manipulating Writeable Terminal Devices
Attack Pattern ID: 40 (Detailed Attack Pattern Completeness: Complete)Typical Severity: Very HighStatus: Draft
+ Description


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


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.

+ Related Weaknesses
CWE-IDWeakness NameWeakness Relationship Type
306Missing Authentication for Critical FunctionTargeted
74Failure to Sanitize Data into a Different Plane ('Injection')Targeted
+ Related Attack Patterns
NatureTypeIDNameDescriptionView(s) this relationship pertains toView\(s\)
ChildOfAttack PatternAttack Pattern249Character Injection 
Mechanism of Attack (primary)1000
+ Purposes
  • Exploitation
+ CIA Impact
Confidentiality Impact: HighIntegrity Impact: HighAvailability Impact: Low
+ Technical Context
Architectural Paradigms
+ References
G. Hoglund and G. McGraw. "Exploiting Software: How to Break Code". Addison-Wesley. February 2004.
+ Content History
G. Hoglund and G. McGraw. Exploiting Software: How to Break Code. Addison-Wesley, February 2004.Cigital, Inc2007-01-01
Gunnar PetersonCigital, Inc2007-02-28Fleshed out content to CAPEC schema from the original descriptions in "Exploiting Software"
Sean BarnumCigital, Inc2007-03-09Review and revise
Richard StruseVOXEM, Inc2007-03-26Review and feedback leading to changes in Name, Description and Examples
Sean BarnumCigital, Inc2007-04-13Modified pattern content according to review and feedback