Command Injection Defense Cheat Sheet - Revision history

Jmanico: rename

2017-11-13T18:22:13Z

rename

Jmanico: Added TODO

2017-11-13T18:17:23Z

Added TODO

Jmanico: /* Primary Defenses */

2017-11-13T18:16:47Z

‎Primary Defenses

Jmanico: Adding Katy Antons work

2017-11-13T18:15:01Z

Adding Katy Antons work

Jmanico: removed work in progress

2017-11-13T18:13:53Z

removed work in progress

Jmanico: /* Introduction */

2017-03-09T03:22:27Z

‎Introduction

Skawtus: /* WORK IN PROGRESS */

2016-08-09T23:41:46Z

‎WORK IN PROGRESS

Skawtus: /* Introduction */

2016-08-09T23:41:15Z

‎Introduction

Skawtus: /* Introduction */

2016-08-09T23:39:00Z

‎Introduction

Skawtus: /* Authors and Primary Editors */

2016-08-09T23:29:49Z

‎Authors and Primary Editors

← Older revision		Revision as of 18:22, 13 November 2017
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−	~~__NOTOC__~~	+	#REDIRECT [[OS_Command_Injection_Defense_Cheat_Sheet]]
−	~~<div style="width:100%;height:160px;border:0,margin:0;overflow: hidden;">[[File:Cheatsheets-header.jpg\|link=]]</div>~~
−
−	~~{\| style="padding: 0;margin:0;margin-top:10px;text-align:left;" \|-~~
−	~~\| valign="top" style="border-right: 1px dotted gray;padding-right:25px;" \|~~
−	~~Last revision (08/09/16): '''{{REVISIONMONTH}}/{{REVISIONDAY}}/{{REVISIONYEAR}}'''~~
−
−	~~== Introduction ==~~
−
−	Command injection (or OS Command Injection) is a type of injection where the software, that constructs a system command using externally influenced input, does not correctly neutralizes the input from special elements that can modify the initially intended command.
−
−	~~For example, if the supplied value is:~~
−	~~<pre>~~
−	~~calc~~
−	~~</pre>~~
−	~~when typed in a Windows command prompt, the application “Calculator” is displayed.~~
−
−	~~However, if the supplied value has been tempered with, and now it is:~~
−	~~<pre>~~
−	~~calc & echo “test”~~
−	~~</pre>~~
−	~~when execute, it changes the meaning of the initial intended value. Now, both the “Calculator” application and the value “test” are displayed.~~
−	~~[[File:Comand-Injection.png\|center\|thumb]]~~
−
−	The problem is exacerbated if the compromised process does not follow the principle of least privilege principle and attacker-controlled commands end up running with special system privileges that increases the amount of damage.
−
−
−	~~== Primary Defenses ==~~
−
−	~~=== Defense Option 1: Avoid calling OS commands directly ===~~
−	The primary defense is to avoid calling OS commands directly. Built-in library functions are a very good alternative to OS Commands, and they cannot be manipulated to perform tasks other than those it is intended to do.
−
−	~~For example use “mkdir()” instead of system(“mkdir /dir_name”).~~
−
−	~~If there are available libraries or APIs for the language you used, this is the preferred method.~~
−
−	~~=== Defense option 2: Escape values added to OS commands specific to each OS ===~~
−
−	~~<b>TODO</b>~~
−	* For examples, see escapeshellarg() or escapeshellcmd() in PHP.
−
−	~~=== Defense option 3: Parametrization in conjunction with Input Validation ===~~
−
−	~~If it is considered unavoidable the call to a system command incorporated with user-supplied, the following two layers of defense should be used within software in order to prevent attacks~~
−	# '''Parametrization''' - If available, use structured mechanisms that automatically enforce the separation between data and command. These mechanisms can help to provide the relevant quoting, encoding.
−	~~# '''Input validation''' - the values for commands and the relevant arguments should be both validated. There are different degrees of validation for the actual command and its arguments:~~
−	#* When it comes to the '''commands''' used, these must be validated against a whitelist of allowed commands.
−	~~#* In regards to the '''arguments''' used for these commands, they should be validated using the following options:~~
−	~~#** Positive or “whitelist” input validation - where are the arguments allowed explicitly defined~~
−	#** White list Regular Expression - where is explicitly defined a whitelist of good characters allowed and the maximum length of the string. Ensure that metacharacters like & \| ; $ > < ` \ ! and white-spaces are not part of the Regular Expression. For example, the following regular expression only allows lowercase letters and numbers, and does not contain metacharacters. The length is also being limited to 3-10 characters:
−	~~<pre>~~
−	~~^[a-z0-9]{3,10}$~~
−	~~</pre>~~
−
−	~~== Additional Defenses ==~~
−
−	~~=== Least privilege ===~~
−	~~On top of primary defences, parameterizations and input validation, we also recommend adopting all of these additional defenses in order to provide defense in depth.~~
−
−	~~These additional defenses are:~~
−	*Applications should run using the lowest privileges that are required to accomplish the necessary tasks.
−	*If possible, create isolated accounts with limited privileges that are only used for a single task.
−
−	~~== Code examples ==~~
−
−	~~=== C/C++ ===~~
−	~~Use function from exec() family ( execl(), execve(), etc., instead of system().~~
−
−	~~The exec family of functions does not use a full shell interpreter, so it is not vulnerable to command-injection attacks.~~
−
−	~~=== Java ===~~
−	~~In Java, use ProcessBuilder and the command must be separated from its arguments.~~
−
−	~~'''''Incorrect Usage'''''<pre>~~
−	~~ProcessBuilder b = new ProcessBuilder("C:\DoStuff.exe -arg1 -arg2");~~
−	~~</pre>~~
−	~~In this example, the command together with the arguments are passed as a one string, making easy to manipulate that expression and inject malicious strings.~~
−
−	~~'''''Correct Usage'''''~~
−
−	Here is an example that starts a process with a modified working directory. The command and each of the arguments are passed separately. This make it easy to validated each term and reduces the risk to insert malicious strings.
−
−	~~<pre>~~
−	~~ProcessBuilder pb = new ProcessBuilder("TrustedCmd", "TrustedArg1", "TrustedArg2");~~
−	~~Map<String, String> env = pb.environment();~~
−
−	~~pb.directory(new File("TrustedDir"));~~
−
−	~~Process p = pb.start();~~
−	~~</pre>~~
−
−	~~=== PHP ===~~
−	~~In PHP use escapeshellarg() or escapeshellcmd() rather than exec(), system(), passthru().~~
−
−	~~== Related articles ==~~
−	~~'''Description of Command Injection Vulnerability'''~~
−	* [[Command Injection\|OWASP Command Injection]]
−
−	~~'''How to Avoid Vulnerabilities'''~~
−	* C Coding: [https://www.securecoding.cert.org/confluence/pages/viewpage.action?pageId=2130132 Do not call system()]
−	~~'''How to Review Code'''~~
−	* OWASP - [[Reviewing Code for OS Injection]]
−
−	~~'''How to Test'''~~
−	* [[OWASP Testing Guide]] article on [[Testing for Command Injection]]
−
−	~~'''External References'''~~
−	* [https://cwe.mitre.org/data/definitions/77.html CWE Entry 77 on Command Injection]
−
−	~~== Other Cheatsheets ==~~
−
−	~~{{Cheatsheet_Navigation_Body}}~~
−
−	\|}
−
−	[[~~Category:Cheatsheets~~]]

← Older revision		Revision as of 18:17, 13 November 2017
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	<b>TODO</b>		<b>TODO</b>
		+	* For examples, see escapeshellarg() or escapeshellcmd() in PHP.

	=== Defense option 3: Parametrization in conjunction with Input Validation ===		=== Defense option 3: Parametrization in conjunction with Input Validation ===

@@ Line 35: / Line 35: @@
 If there are available libraries or APIs for the language you used, this is the preferred method.
-=== Defense option 2: Parametrization  in conjunction with Input Validation ===
+=== Defense option 2: Escape values added to OS commands specific to each OS  ===
 If it is considered unavoidable the call to a system command incorporated with user-supplied, the following two layers of defense should be used within software in order to prevent attacks
@@ Line 47: / Line 51: @@
   ^[a-z0-9]{3,10}$
 </pre>
 == Additional Defenses ==

@@ Line 6: / Line 6: @@
 Last revision (08/09/16): '''{{REVISIONMONTH}}/{{REVISIONDAY}}/{{REVISIONYEAR}}'''
-= Introduction  =
+== Introduction ==
-  __TOC__{{TOC hidden}}
-This cheat sheet provides some best practice for developers to follow to avoid the risk of [[Command Injection]]<br>
+For example, if the supplied value is:
-= Introduction =
+However, if the supplied value has been tempered with, and now it is:
-) What is Command Injection?
+The problem is exacerbated if the compromised process does not follow the principle of least privilege principle and attacker-controlled commands end up running with special system privileges that increases the amount of damage.
-) Safe design for features where OS interaction is intentional
+== Primary Defenses  ==
-b)  TBD codegen example?
+=== Defense Option 1: Avoid calling OS commands directly ===
-c) TBD example
+For example use “mkdir()” instead of system(“mkdir /dir_name”).
-) Summary
+If there are available libraries or APIs for the language you used, this is the preferred method.
-TBD takeaway language agnostic approaches list
+=== Defense option 2: Parametrization  in conjunction with Input Validation ===
-= Details =
+If it is considered unavoidable the call to a system command incorporated with user-supplied, the following two layers of defense should be used within software in order to prevent attacks
-TBD
+=== Least privilege ===
-= Authors and Primary Editors  =
+These additional defenses are:
-Jim Manico - jim[at]owasp.org
+== Code examples ==
-Scott Davis - scott_davis[at]rapid7.com
+=== C/C++ ===
 == Other Cheatsheets ==
@@ Line 53: / Line 107: @@
 |}
 [[Category:Cheatsheets]]

← Older revision		Revision as of 18:13, 13 November 2017
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−	~~= WORK IN PROGRESS =~~
−
	__NOTOC__		__NOTOC__
	<div style="width:100%;height:160px;border:0,margin:0;overflow: hidden;">[[File:Cheatsheets-header.jpg\|link=]]</div>		<div style="width:100%;height:160px;border:0,margin:0;overflow: hidden;">[[File:Cheatsheets-header.jpg\|link=]]</div>

@@ Line 29: / Line 29: @@
 a) Like safely calling ImageMagik to do image manipulation, etc
-b)  TBD example
+b)  TBD codegen example?
 c) TBD example

← Older revision		Revision as of 23:29, 9 August 2016
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	Jim Manico - jim[at]owasp.org		Jim Manico - jim[at]owasp.org
		+
	Scott Davis - scott_davis[at]rapid7.com		Scott Davis - scott_davis[at]rapid7.com