Summary

Attack 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.

   Attack Step Techniques

   ID	Attack Step Technique Description	Environments
   1	Port mapping. Identify ports that the system is listening on, and attempt to identify inputs and protocol types on those ports.	env-Local env-CommProtocol env-Peer2Peer env-ClientServer
   2	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, he attempts to guess the actual operating system.	env-Embedded env-ClientServer env-Peer2Peer env-CommProtocol env-Web
   3	Induce errors to find informative error messages	env-All

   Indicators

   ID	type	Indicator Description	Environments
   1	Positive	The target software accepts connections via the network.	env-Web env-CommProtocol env-Peer2Peer env-Embedded env-ClientServer

   Outcomes

   ID	type	Outcome Description
   1	Success	Operating environment (operating system, language, and/or middleware) is correctly identified.
   2	Inconclusive	Multiple candidate operating environments are suggested.

   Security Controls

   ID	type	Security Control Description
   1	Preventative	Provide misleading information on TCIP/IP fingerprints (some operating systems can be configured to send signatures that match other operating systems).
   2	Preventative	Provide misleading information at the server level (e.g., Apache, IIS, WebLogic, etc.) to announce a different server software.
   3	Detective	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

   ID	Attack Step Technique Description	Environments
   1	Spidering web sites for all available links	env-Web
   2	Inventory all application inputs	env-All

   Indicators

   ID	type	Indicator Description	Environments
   1	Positive	Attacker develops a list of valid inputs	env-All

   Outcomes

   ID	type	Outcome Description
   1	Success	The attacker develops a list of likely command delimiters.

   Security Controls

   ID	type	Security Control Description
   1	Detective	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).
   2	Detective	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.
   3	Preventative	Actively monitor the application and either deny or redirect requests from origins that appear to be automated.
   4	Detective	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. 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

   Attack Step Techniques

   ID	Attack Step Technique Description	Environments
   1	Inject command delimiters using network packet injection tools (netcat, nemesis, etc.)	env-CommProtocol env-Web env-Peer2Peer env-ClientServer
   2	Inject command delimiters using web test frameworks (proxies, TamperData, custom programs, etc.)	env-Web

   Indicators

   ID	type	Indicator Description	Environments
   1	Positive	Inventorying in prior step is successful.	env-All

   Outcomes

   ID	type	Outcome Description
   1	Success	One or more injections that are appropriate to the platform provokes an unexpected response from the software, which can be varied by the attacker based on the input.

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.

   Attack Step Techniques

   ID	Attack Step Technique Description	Environments
   1	The attacker executes a command that stores sensitive information into a location where he can retrieve it later (perhaps using a different command injection).	env-All
   2	The attacker executes a command that stores sensitive information into a location where he can retrieve it later (perhaps using a different command injection).	env-All
   3	The attacker executes a command that stores sensitive information into a location where he can retrieve it later (perhaps using a different command injection).	env-All

   Outcomes

   ID	type	Outcome Description
   1	Success	The software performs an action the attacker desires. This might be displaying information, storing a program, executing a command, or some other malicious activity.

   Security Controls

   ID	type	Security Control Description
   1	Preventative	Make commonly exploited administrative tools log their execution.
   2	Preventative	Make commonly exploited administrative tools non-executable, except when the system is in specific maintenance periods. (i.e., require administrators to specifically enable certain administrative commands prior to performing system maintenance.)

Likelihood: High

There is high motivation for the attacker to seek out and discover opportunities for this attack due to the power it yields.

Description

Related Vulnerabilities

Skill or Knowledge 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.

Use language APIs rather than relying on passing data to the oeprating 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.

Secunia Advisory SA16869: Firefox Command Line URL Shell Command Injection