Command Delimiters
Attack Pattern ID: 15 (Standard Attack Pattern Completeness: Complete)Typical Severity: HighStatus: Draft
+ Description


An attack of this type exploits a programs' vulnerabilities that allows an attacker's commands to be concatenated onto a legitimate command with the intent of targeting other resources such as the file system or database. The system that uses a filter or a blacklist input validation, as opposed to whitelist validation is vulnerable to an attacker who predicts delimiters (or combinations of delimiters) not present in the filter or blacklist. As with other injection attacks, the attacker uses the command delimiter payload as an entry point to tunnel through the application and activate additional attacks through SQL queries, shell commands, network scanning, and so on.

Attack Execution Flow

  1. Assess Target Runtime Environment:

    In situations where the runtime environment is not implicitly known, the attacker makes connections to the target system and tries to determine the system's runtime environment. Knowing the environment is vital to choosing the correct delimiters.

    Attack Step Techniques

    IDAttack Step Technique DescriptionEnvironments

    Port mapping using network connection-based software (e.g., nmap, nessus, etc.)

    env-ClientServer env-Embedded env-CommProtocol env-Peer2Peer env-Web

    Port mapping by exploring the operating system (netstat, sockstat, etc.)


    TCP/IP Fingerprinting


    Induce errors to find informative error messages



    IDtypeIndicator DescriptionEnvironments

    The target software accepts connections via the network.

    env-Web env-CommProtocol env-Peer2Peer env-Embedded


    IDtypeOutcome Description
    Operating environment (operating system, language, and/or middleware) is correctly identified.
    Multiple candidate operating environments are suggested.

    Security Controls

    IDtypeSecurity Control Description
    Provide misleading information on TCIP/IP fingerprints (some operating systems can be configured to send signatures that match other operating systems).
    Provide misleading information at the server level (e.g., Apache, IIS, WebLogic, etc.) to announce a different server software.
    Some fingerprinting techniques can be detected by operating systems or by network IDS systems because they leave the network connection half-open, or they do not belong to a valid, open connection.
  2. Survey the Application:

    The attacker surveys the target application, possibly as a valid and authenticated user

    Attack Step Techniques

    IDAttack Step Technique DescriptionEnvironments

    Spidering web sites for all available links


    Inventory all application inputs



    IDtypeIndicator DescriptionEnvironments

    Attacker develops a list of valid inputs

    env-Web env-ClientServer


    IDtypeOutcome Description
    The attacker develops a list of likely command delimiters.

    Security Controls

    IDtypeSecurity Control Description
    Monitor velocity of page fetching in web logs. Humans who view a page and select a link from it will click far slower and far less regularly than tools. Tools make requests very quickly and the requests are typically spaced apart regularly (e.g. 0.8 seconds between them).
    Create links on some pages that are visually hidden from web browsers. Using IFRAMES, images, or other HTML techniques, the links can be hidden from web browsing humans, but visible to spiders and programs. A request for the page, then, becomes a good predictor of an automated tool probing the application.
    Actively monitor the application and either deny or redirect requests from origins that appear to be automated.
    Monitor velocity of feature activations (non-web software). Humans who activate features (click buttons, request actions, invoke APIs, etc.) will do so far slower and far less regularly than tools. Tools make requests very quickly and the requests are typically spaced apart regularly (e.g. 0.8 seconds between them).
  1. Attempt delimiters in inputs:

    The attacker systematically attempts variations of delimiters on known inputs, observing the application's response each time.

    Attack Step Techniques

    IDAttack Step Technique DescriptionEnvironments

    SecurityDatabase\Alert\Inject command delimiters using network packet injection tools (netcat, nemesis, etc.)

    env-CommProtocol env-Web env-Peer2Peer env-ClientServer

    SecurityDatabase\Alert\Inject command delimiters using web test frameworks (proxies, TamperData, custom programs, etc.)


    Enter command delimiters directly in input fields.

    env-Embedded env-Local env-ClientServer


    IDtypeIndicator DescriptionEnvironments

    Attack step 2 is successful.



    IDtypeOutcome Description
    One or more command delimiters for the platform provokes an unexpected response from the software, which can be varied by the attacker based on the input.
  1. Use malicious command delimiters:

    The attacker uses combinations of payload and carefully placed command delimiters to attack the software.


    IDtypeOutcome Description
    The software performs as expected by the attacker.

    Security Controls

    IDtypeSecurity Control Description
+ Attack Prerequisites

Software's input validation or filtering must not detect and block presence of additional malicious command.

+ Typical Likelihood of Exploit

Likelihood: High

+ Methods of Attack
  • Injection
+ Examples-Instances


By appending special characters, such as a semicolon or other commands that are executed by the target process, the attacker is able to execute a wide variety of malicious commands in the target process space, utilizing the target's inherited permissions, against any resource the host has access to. The possibilities are vast including injection attacks against RDBMS (SQL Injection), directory servers (LDAP Injection), XML documents (XPath and XQuery Injection), and command line shells. In many injection attacks, the results are converted back to strings and displayed to the client process such as a web browser without tripping any security alarms, so the network firewall does not log any out of the ordinary behavior.

LDAP servers house critical identity assets such as user, profile, password, and group information that is used to authenticate and authorize users. An attacker that can query the directory at will and execute custom commands against the directory server is literally working with the keys to the kingdom in many enterprises. When user, organizational units, and other directory objects are queried by building the query string directly from user input with no validation, or other conversion, then the attacker has the ability to use any LDAP commands to query, filter, list, and crawl against the LDAP server directly in the same manner as SQL injection gives the ability to the attacker to run SQL commands on the database.

+ Attacker Skills or Knowledge Required

Skill or Knowledge Level: Medium

The attacker has to identify injection vector, identify the specific commands, and optionally collect the output, i.e. from an interactive session.

+ Resources Required

Ability to communicate synchronously or asynchronously with server. Optionally, ability to capture output directly through synchronous communication or other method such as FTP.

+ Solutions and Mitigations

Design: Perform whitelist validation against a positive specification for command length, type, and parameters.

Design: Limit program privileges, so if commands circumvent program input validation or filter routines then commands do not running under a privileged account

Implementation: Perform input validation for all remote content.

Implementation: Use type conversions such as JDBC prepared statements.

+ Attack Motivation-Consequences
  • Run Arbitrary Code
  • Information Leakage
+ Injection Vector

Malicious input delivered through appending delimiters to standard input

+ Payload

Command(s) appended to valid parameters to enable attacker to execute commands on host

+ Activation Zone

Client machine and client network

+ 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
146Improper Neutralization of Expression/Command DelimitersTargeted
77Improper Sanitization of Special Elements used in a Command ('Command Injection')Targeted
184Incomplete BlacklistTargeted
78Improper Sanitization of Special Elements used in an OS Command ('OS Command Injection')Targeted
185Incorrect Regular ExpressionTargeted
93Failure to Sanitize CRLF Sequences ('CRLF Injection')Targeted
140Failure to Sanitize DelimitersTargeted
157Failure to Sanitize Paired DelimitersTargeted
138Improper Neutralization of Special ElementsTargeted
154Improper Neutralization of Variable Name DelimitersTargeted
697Insufficient ComparisonTargeted
713OWASP Top Ten 2007 Category A2 - Injection FlawsTargeted
+ Related Attack Patterns
NatureTypeIDNameDescriptionView(s) this relationship pertains toView\(s\)
ChildOfAttack PatternAttack Pattern6Argument Injection 
Mechanism of Attack1000
ChildOfAttack PatternAttack Pattern248Command Injection 
Mechanism of Attack (primary)1000
ParentOfAttack PatternAttack Pattern88OS Command Injection 
Mechanism of Attack (primary)1000
+ Purposes
  • Penetration
+ CIA Impact
Confidentiality Impact: HighIntegrity Impact: HighAvailability Impact: High
+ 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
Paco HopeCigital, Inc.2007-10-20Added extended Attack Execution Flow