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CAPEC-88: OS Command Injection

Attack Pattern ID: 88
Abstraction: Standard
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+ Description
In this type of an attack, an adversary injects operating system commands into existing application functions. An application that uses untrusted input to build command strings is vulnerable. An adversary can leverage OS command injection in an application to elevate privileges, execute arbitrary commands and compromise the underlying operating system.
+ Likelihood Of Attack


+ Typical Severity


+ Relationships
Section HelpThis table shows the other attack patterns and high level categories that are related to this attack pattern. These relationships are defined as ChildOf and ParentOf, and give insight to similar items that may exist at higher and lower levels of abstraction. In addition, relationships such as CanFollow, PeerOf, and CanAlsoBe are defined to show similar attack patterns that the user may want to explore.
ChildOfMeta Attack PatternMeta Attack Pattern - A meta level attack pattern in CAPEC is a decidedly abstract characterization of a specific methodology or technique used in an attack. A meta attack pattern is often void of a specific technology or implementation and is meant to provide an understanding of a high level approach. A meta level attack pattern is a generalization of related group of standard level attack patterns. Meta level attack patterns are particularly useful for architecture and design level threat modeling exercises.248Command Injection
Section HelpThis table shows the views that this attack pattern belongs to and top level categories within that view.
+ Execution Flow
  1. Identify inputs for OS commands: The attacker determines user controllable input that gets passed as part of a command to the underlying operating system.

    Port mapping. Identify ports that the system is listening on, and attempt to identify inputs and protocol types on those ports.
    TCP/IP Fingerprinting. The attacker uses various software to make connections or partial connections and observe idiosyncratic responses from the operating system. Using those responses, they attempt to guess the actual operating system.
    Induce errors to find informative error messages
  2. Survey the Application: The attacker surveys the target application, possibly as a valid and authenticated user

    Spidering web sites for all available links
    Inventory all application inputs
  1. Vary inputs, looking for malicious results.: Depending on whether the application being exploited is a remote or local one the attacker crafts the appropriate malicious input, containing OS commands, to be passed to the application

    Inject command delimiters using network packet injection tools (netcat, nemesis, etc.)
    Inject command delimiters using web test frameworks (proxies, TamperData, custom programs, etc.)
  1. Execute malicious commands: The attacker may steal information, install a back door access mechanism, elevate privileges or compromise the system in some other way.

    The attacker executes a command that stores sensitive information into a location where they can retrieve it later (perhaps using a different command injection).
+ Prerequisites
User controllable input used as part of commands to the underlying operating system.
+ Skills Required
[Level: High]
The attacker needs to have knowledge of not only the application to exploit but also the exact nature of commands that pertain to the target operating system. This may involve, though not always, knowledge of specific assembly commands for the platform.
+ Consequences
Section HelpThis table specifies different individual consequences associated with the attack pattern. The Scope identifies the security property that is violated, while the Impact describes the negative technical impact that arises if an adversary succeeds in their attack. The Likelihood provides information about how likely the specific consequence is expected to be seen relative to the other consequences in the list. For example, there may be high likelihood that a pattern will be used to achieve a certain impact, but a low likelihood that it will be exploited to achieve a different impact.
Execute Unauthorized Commands
Access Control
Gain Privileges
Bypass Protection Mechanism
Read Data
+ Mitigations
Use language APIs rather than relying on passing data to the operating system shell or command line. Doing so ensures that the available protection mechanisms in the language are intact and applicable.
Filter all incoming data to escape or remove characters or strings that can be potentially misinterpreted as operating system or shell commands
All application processes should be run with the minimal privileges required. Also, processes must shed privileges as soon as they no longer require them.
+ Example Instances

A transaction processing system relies on code written in a number of languages. To access this functionality, the system passes transaction information on the system command line.

An attacker can gain access to the system command line and execute malicious commands by injecting these commands in the transaction data. If successful, the attacker can steal information, install backdoors and perform other nefarious activities that can compromise the system and its data.

See also: A vulnerability in Mozilla Firefox 1.x browser allows an attacker to execute arbitrary commands on the UNIX/Linux operating system. The vulnerability is caused due to the shell script used to launch Firefox parsing shell commands that are enclosed within back-ticks in the URL provided via the command line. This can be exploited to execute arbitrary shell commands by tricking a user into following a malicious link in an external application which uses Firefox as the default browser (e.g. the mail client Evolution on Red Hat Enterprise Linux 4).
+ Taxonomy Mappings
Relevant to the WASC taxonomy mapping
Entry IDEntry Name
31OS Commanding
+ References
[REF-543] "Secunia Advisory SA16869: Firefox Command Line URL Shell Command Injection". Secunia Advisories. Secunia. 2005-09-20. <>.
+ Content History
Submission DateSubmitterOrganization
(Version 2.6)
CAPEC Content TeamThe MITRE Corporation
Modification DateModifierOrganization
(Version 3.3)
CAPEC Content TeamThe MITRE Corporation
Updated Execution_Flow
(Version 3.4)
CAPEC Content TeamThe MITRE Corporation
Updated Taxonomy_Mappings
(Version 3.5)
CAPEC Content TeamThe MITRE Corporation
Updated Execution_Flow, Related_Weaknesses
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Page Last Updated or Reviewed: July 31, 2018