CWE - CWE-77: Improper Neutralization of Special Elements used in a Command ('Command Injection') (4.10)

Weakness ID: 77

Abstraction: Class
Structure: Simple

View customized information:

Description

The product constructs all or part of a command using externally-influenced input from an upstream component, but it does not neutralize or incorrectly neutralizes special elements that could modify the intended command when it is sent to a downstream component.

Extended Description

Command injection vulnerabilities typically occur when:

1. Data enters the application from an untrusted source.

2. The data is part of a string that is executed as a command by the application.

3. By executing the command, the application gives an attacker a privilege or capability that the attacker would not otherwise have.

Many protocols and products have their own custom command language. While OS or shell command strings are frequently discovered and targeted, developers may not realize that these other command languages might also be vulnerable to attacks.

Command injection is a common problem with wrapper programs.

Relationships

This table shows the weaknesses and high level categories that are related to this weakness. These relationships are defined as ChildOf, ParentOf, MemberOf and give insight to similar items that may exist at higher and lower levels of abstraction. In addition, relationships such as PeerOf and CanAlsoBe are defined to show similar weaknesses that the user may want to explore.

Relevant to the view "Research Concepts" (CWE-1000)

Nature	Type	ID	Name
ChildOf	Class - a weakness that is described in a very abstract fashion, typically independent of any specific language or technology. More specific than a Pillar Weakness, but more general than a Base Weakness. Class level weaknesses typically describe issues in terms of 1 or 2 of the following dimensions: behavior, property, and resource.	74	Improper Neutralization of Special Elements in Output Used by a Downstream Component ('Injection')
ParentOf	Base - a weakness that is still mostly independent of a resource or technology, but with sufficient details to provide specific methods for detection and prevention. Base level weaknesses typically describe issues in terms of 2 or 3 of the following dimensions: behavior, property, technology, language, and resource.	78	Improper Neutralization of Special Elements used in an OS Command ('OS Command Injection')
ParentOf	Base - a weakness that is still mostly independent of a resource or technology, but with sufficient details to provide specific methods for detection and prevention. Base level weaknesses typically describe issues in terms of 2 or 3 of the following dimensions: behavior, property, technology, language, and resource.	88	Improper Neutralization of Argument Delimiters in a Command ('Argument Injection')
ParentOf	Base - a weakness that is still mostly independent of a resource or technology, but with sufficient details to provide specific methods for detection and prevention. Base level weaknesses typically describe issues in terms of 2 or 3 of the following dimensions: behavior, property, technology, language, and resource.	624	Executable Regular Expression Error
ParentOf	Base - a weakness that is still mostly independent of a resource or technology, but with sufficient details to provide specific methods for detection and prevention. Base level weaknesses typically describe issues in terms of 2 or 3 of the following dimensions: behavior, property, technology, language, and resource.	917	Improper Neutralization of Special Elements used in an Expression Language Statement ('Expression Language Injection')

Relevant to the view "Weaknesses for Simplified Mapping of Published Vulnerabilities" (CWE-1003)

Nature	Type	ID	Name
ChildOf	Class - a weakness that is described in a very abstract fashion, typically independent of any specific language or technology. More specific than a Pillar Weakness, but more general than a Base Weakness. Class level weaknesses typically describe issues in terms of 1 or 2 of the following dimensions: behavior, property, and resource.	74	Improper Neutralization of Special Elements in Output Used by a Downstream Component ('Injection')

Relevant to the view "Architectural Concepts" (CWE-1008)

Nature	Type	ID	Name
MemberOf	Category - a CWE entry that contains a set of other entries that share a common characteristic.	1019	Validate Inputs

Relevant to the view "CISQ Quality Measures (2020)" (CWE-1305)

Nature	Type	ID	Name
ParentOf	Base - a weakness that is still mostly independent of a resource or technology, but with sufficient details to provide specific methods for detection and prevention. Base level weaknesses typically describe issues in terms of 2 or 3 of the following dimensions: behavior, property, technology, language, and resource.	78	Improper Neutralization of Special Elements used in an OS Command ('OS Command Injection')
ParentOf	Base - a weakness that is still mostly independent of a resource or technology, but with sufficient details to provide specific methods for detection and prevention. Base level weaknesses typically describe issues in terms of 2 or 3 of the following dimensions: behavior, property, technology, language, and resource.	88	Improper Neutralization of Argument Delimiters in a Command ('Argument Injection')
ParentOf	Base - a weakness that is still mostly independent of a resource or technology, but with sufficient details to provide specific methods for detection and prevention. Base level weaknesses typically describe issues in terms of 2 or 3 of the following dimensions: behavior, property, technology, language, and resource.	624	Executable Regular Expression Error
ParentOf	Base - a weakness that is still mostly independent of a resource or technology, but with sufficient details to provide specific methods for detection and prevention. Base level weaknesses typically describe issues in terms of 2 or 3 of the following dimensions: behavior, property, technology, language, and resource.	917	Improper Neutralization of Special Elements used in an Expression Language Statement ('Expression Language Injection')

Relevant to the view "CISQ Data Protection Measures" (CWE-1340)

Nature	Type	ID	Name
ParentOf	Base - a weakness that is still mostly independent of a resource or technology, but with sufficient details to provide specific methods for detection and prevention. Base level weaknesses typically describe issues in terms of 2 or 3 of the following dimensions: behavior, property, technology, language, and resource.	78	Improper Neutralization of Special Elements used in an OS Command ('OS Command Injection')
ParentOf	Base - a weakness that is still mostly independent of a resource or technology, but with sufficient details to provide specific methods for detection and prevention. Base level weaknesses typically describe issues in terms of 2 or 3 of the following dimensions: behavior, property, technology, language, and resource.	88	Improper Neutralization of Argument Delimiters in a Command ('Argument Injection')
ParentOf	Base - a weakness that is still mostly independent of a resource or technology, but with sufficient details to provide specific methods for detection and prevention. Base level weaknesses typically describe issues in terms of 2 or 3 of the following dimensions: behavior, property, technology, language, and resource.	624	Executable Regular Expression Error
ParentOf	Base - a weakness that is still mostly independent of a resource or technology, but with sufficient details to provide specific methods for detection and prevention. Base level weaknesses typically describe issues in terms of 2 or 3 of the following dimensions: behavior, property, technology, language, and resource.	917	Improper Neutralization of Special Elements used in an Expression Language Statement ('Expression Language Injection')

Modes Of Introduction

The different Modes of Introduction provide information about how and when this weakness may be introduced. The Phase identifies a point in the life cycle at which introduction may occur, while the Note provides a typical scenario related to introduction during the given phase.

Phase	Note
Architecture and Design
Implementation	REALIZATION: This weakness is caused during implementation of an architectural security tactic.

Applicable Platforms

This listing shows possible areas for which the given weakness could appear. These may be for specific named Languages, Operating Systems, Architectures, Paradigms, Technologies, or a class of such platforms. The platform is listed along with how frequently the given weakness appears for that instance.

Languages

Class: Not Language-Specific (Undetermined Prevalence)

Common Consequences

This table specifies different individual consequences associated with the weakness. The Scope identifies the application security area that is violated, while the Impact describes the negative technical impact that arises if an adversary succeeds in exploiting this weakness. 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 weakness will be exploited to achieve a certain impact, but a low likelihood that it will be exploited to achieve a different impact.

Scope	Impact	Likelihood
Integrity Confidentiality Availability	Technical Impact: Execute Unauthorized Code or Commands If a malicious user injects a character (such as a semi-colon) that delimits the end of one command and the beginning of another, it may be possible to then insert an entirely new and unrelated command that was not intended to be executed.

Likelihood Of Exploit

High

Demonstrative Examples

Example 1

The following simple program accepts a filename as a command line argument and displays the contents of the file back to the user. The program is installed setuid root because it is intended for use as a learning tool to allow system administrators in-training to inspect privileged system files without giving them the ability to modify them or damage the system.

(bad code)

Example Language: C

int main(int argc, char** argv) {

char cmd[CMD_MAX] = "/usr/bin/cat ";
strcat(cmd, argv[1]);
system(cmd);

}

Because the program runs with root privileges, the call to system() also executes with root privileges. If a user specifies a standard filename, the call works as expected. However, if an attacker passes a string of the form ";rm -rf /", then the call to system() fails to execute cat due to a lack of arguments and then plows on to recursively delete the contents of the root partition.

Note that if argv[1] is a very long argument, then this issue might also be subject to a buffer overflow (CWE-120).

Example 2

The following code is from an administrative web application designed to allow users to kick off a backup of an Oracle database using a batch-file wrapper around the rman utility and then run a cleanup.bat script to delete some temporary files. The script rmanDB.bat accepts a single command line parameter, which specifies what type of backup to perform. Because access to the database is restricted, the application runs the backup as a privileged user.

(bad code)

Example Language: Java

...
String btype = request.getParameter("backuptype");
String cmd = new String("cmd.exe /K \"

c:\\util\\rmanDB.bat "
+btype+
"&&c:\\utl\\cleanup.bat\"")

System.Runtime.getRuntime().exec(cmd);
...

The problem here is that the program does not do any validation on the backuptype parameter read from the user. Typically the Runtime.exec() function will not execute multiple commands, but in this case the program first runs the cmd.exe shell in order to run multiple commands with a single call to Runtime.exec(). Once the shell is invoked, it will happily execute multiple commands separated by two ampersands. If an attacker passes a string of the form "& del c:\\dbms\\*.*", then the application will execute this command along with the others specified by the program. Because of the nature of the application, it runs with the privileges necessary to interact with the database, which means whatever command the attacker injects will run with those privileges as well.

Example 3

The following code from a system utility uses the system property APPHOME to determine the directory in which it is installed and then executes an initialization script based on a relative path from the specified directory.

(bad code)

Example Language: Java

...
String home = System.getProperty("APPHOME");
String cmd = home + INITCMD;
java.lang.Runtime.getRuntime().exec(cmd);
...

The code above allows an attacker to execute arbitrary commands with the elevated privilege of the application by modifying the system property APPHOME to point to a different path containing a malicious version of INITCMD. Because the program does not validate the value read from the environment, if an attacker can control the value of the system property APPHOME, then they can fool the application into running malicious code and take control of the system.

Example 4

The following code is a wrapper around the UNIX command cat which prints the contents of a file to standard out. It is also injectable:

(bad code)

Example Language: C

#include <stdio.h>
#include <unistd.h>

int main(int argc, char **argv) {

char cat[] = "cat ";
char *command;
size_t commandLength;

commandLength = strlen(cat) + strlen(argv[1]) + 1;
command = (char *) malloc(commandLength);
strncpy(command, cat, commandLength);
strncat(command, argv[1], (commandLength - strlen(cat)) );

system(command);
return (0);

}

Used normally, the output is simply the contents of the file requested:

(informative)

$ ./catWrapper Story.txt
When last we left our heroes...

However, if we add a semicolon and another command to the end of this line, the command is executed by catWrapper with no complaint:

(attack code)

$ ./catWrapper Story.txt; ls
When last we left our heroes...
Story.txt
SensitiveFile.txt
PrivateData.db
a.out*

If catWrapper had been set to have a higher privilege level than the standard user, arbitrary commands could be executed with that higher privilege.

Observed Examples

Reference	Description
CVE-2022-36069	Python-based dependency management tool avoids OS command injection when generating Git commands but allows injection of optional arguments with input beginning with a dash, potentially allowing for code execution.
CVE-1999-0067	Canonical example of OS command injection. CGI program does not neutralize "\|" metacharacter when invoking a phonebook program.
CVE-2020-9054	Chain: improper input validation (CWE-20) in username parameter, leading to OS command injection (CWE-78), as exploited in the wild per CISA KEV.
CVE-2022-1509	injection of sed script syntax ("sed injection")
CVE-2021-41282	injection of sed script syntax ("sed injection")
CVE-2019-13398	injection of sed script syntax ("sed injection")
CVE-2019-12921	image program allows injection of commands in "Magick Vector Graphics (MVG)" language.
CVE-2020-11698	anti-spam product allows injection of SNMP commands into confiuration file

Potential Mitigations

Phase: Architecture and Design

If at all possible, use library calls rather than external processes to recreate the desired functionality.

Phase: Implementation

If possible, ensure that all external commands called from the program are statically created.

Phase: Implementation

Strategy: Input Validation

Assume all input is malicious. Use an "accept known good" input validation strategy, i.e., use a list of acceptable inputs that strictly conform to specifications. Reject any input that does not strictly conform to specifications, or transform it into something that does.

When performing input validation, consider all potentially relevant properties, including length, type of input, the full range of acceptable values, missing or extra inputs, syntax, consistency across related fields, and conformance to business rules. As an example of business rule logic, "boat" may be syntactically valid because it only contains alphanumeric characters, but it is not valid if the input is only expected to contain colors such as "red" or "blue."

Do not rely exclusively on looking for malicious or malformed inputs. This is likely to miss at least one undesirable input, especially if the code's environment changes. This can give attackers enough room to bypass the intended validation. However, denylists can be useful for detecting potential attacks or determining which inputs are so malformed that they should be rejected outright.

Phase: Operation

Run time: Run time policy enforcement may be used in an allowlist fashion to prevent use of any non-sanctioned commands.

Phase: System Configuration

Assign permissions that prevent the user from accessing/opening privileged files.

Weakness Ordinalities

Ordinality	Description
Primary	(where the weakness exists independent of other weaknesses)

Memberships

This MemberOf Relationships table shows additional CWE Categories and Views that reference this weakness as a member. This information is often useful in understanding where a weakness fits within the context of external information sources.

Nature	Type	ID	Name
MemberOf	Category - a CWE entry that contains a set of other entries that share a common characteristic.	713	OWASP Top Ten 2007 Category A2 - Injection Flaws
MemberOf	Category - a CWE entry that contains a set of other entries that share a common characteristic.	722	OWASP Top Ten 2004 Category A1 - Unvalidated Input
MemberOf	Category - a CWE entry that contains a set of other entries that share a common characteristic.	727	OWASP Top Ten 2004 Category A6 - Injection Flaws
MemberOf	Category - a CWE entry that contains a set of other entries that share a common characteristic.	929	OWASP Top Ten 2013 Category A1 - Injection
MemberOf	Category - a CWE entry that contains a set of other entries that share a common characteristic.	990	SFP Secondary Cluster: Tainted Input to Command
MemberOf	Category - a CWE entry that contains a set of other entries that share a common characteristic.	1005	7PK - Input Validation and Representation
MemberOf	Category - a CWE entry that contains a set of other entries that share a common characteristic.	1027	OWASP Top Ten 2017 Category A1 - Injection
MemberOf	Category - a CWE entry that contains a set of other entries that share a common characteristic.	1179	SEI CERT Perl Coding Standard - Guidelines 01. Input Validation and Data Sanitization (IDS)
MemberOf	Category - a CWE entry that contains a set of other entries that share a common characteristic.	1308	CISQ Quality Measures - Security
MemberOf	View - a subset of CWE entries that provides a way of examining CWE content. The two main view structures are Slices (flat lists) and Graphs (containing relationships between entries).	1337	Weaknesses in the 2021 CWE Top 25 Most Dangerous Software Weaknesses
MemberOf	View - a subset of CWE entries that provides a way of examining CWE content. The two main view structures are Slices (flat lists) and Graphs (containing relationships between entries).	1340	CISQ Data Protection Measures
MemberOf	Category - a CWE entry that contains a set of other entries that share a common characteristic.	1347	OWASP Top Ten 2021 Category A03:2021 - Injection
MemberOf	View - a subset of CWE entries that provides a way of examining CWE content. The two main view structures are Slices (flat lists) and Graphs (containing relationships between entries).	1387	Weaknesses in the 2022 CWE Top 25 Most Dangerous Software Weaknesses

Notes

Mapping

Use for Mapping: Allowed-with-Review (this CWE ID could be used to map to real-world vulnerabilities in limited situations requiring careful review).

Rationale: CWE-77 is often used when OS command injection (CWE-78) was intended instead [REF-1287].

Comments: if the weakness involves a command language besides OS shell invocation, then CWE-77 could be used.

Terminology

The "command injection" phrase carries different meanings to different people. For some people, it refers to any type of attack that can allow the attacker to execute commands of their own choosing, regardless of how those commands are inserted. The command injection could thus be resultant from another weakness. This usage also includes cases in which the functionality allows the user to specify an entire command, which is then executed; within CWE, this situation might be better regarded as an authorization problem (since an attacker should not be able to specify arbitrary commands.)

Another common usage, which includes CWE-77 and its descendants, involves cases in which the attacker injects separators into the command being constructed.

Taxonomy Mappings

Mapped Taxonomy Name	Node ID	Fit	Mapped Node Name
7 Pernicious Kingdoms			Command Injection
CLASP			Command injection
OWASP Top Ten 2007	A2	CWE More Specific	Injection Flaws
OWASP Top Ten 2004	A1	CWE More Specific	Unvalidated Input
OWASP Top Ten 2004	A6	CWE More Specific	Injection Flaws
Software Fault Patterns	SFP24		Tainted input to command
SEI CERT Perl Coding Standard	IDS34-PL	CWE More Specific	Do not pass untrusted, unsanitized data to a command interpreter

Related Attack Patterns

CAPEC-ID	Attack Pattern Name
CAPEC-136	LDAP Injection
CAPEC-15	Command Delimiters
CAPEC-183	IMAP/SMTP Command Injection
CAPEC-248	Command Injection
CAPEC-40	Manipulating Writeable Terminal Devices
CAPEC-43	Exploiting Multiple Input Interpretation Layers
CAPEC-75	Manipulating Writeable Configuration Files
CAPEC-76	Manipulating Web Input to File System Calls

References

[REF-6] Katrina Tsipenyuk, Brian Chess and Gary McGraw. "Seven Pernicious Kingdoms: A Taxonomy of Software Security Errors". NIST Workshop on Software Security Assurance Tools Techniques and Metrics. NIST. 2005-11-07. <https://samate.nist.gov/SSATTM_Content/papers/Seven%20Pernicious%20Kingdoms%20-%20Taxonomy%20of%20Sw%20Security%20Errors%20-%20Tsipenyuk%20-%20Chess%20-%20McGraw.pdf>.

[REF-140] Greg Hoglund and Gary McGraw. "Exploiting Software: How to Break Code". Addison-Wesley. 2004-02-27. <https://www.amazon.com/Exploiting-Software-How-Break-Code/dp/0201786958>.

[REF-44] Michael Howard, David LeBlanc and John Viega. "24 Deadly Sins of Software Security". "Sin 10: Command Injection." Page 171. McGraw-Hill. 2010.

[REF-1287] MITRE. "Supplemental Details - 2022 CWE Top 25". Details of Problematic Mappings. 2022-06-28. <https://cwe.mitre.org/top25/archive/2022/2022_cwe_top25_supplemental.html#problematicMappingDetails>.

Content History

Submissions
Submission Date	Submitter	Organization
2006-07-19	7 Pernicious Kingdoms
2006-07-19
Contributions
Contribution Date	Contributor	Organization
2022-05-20	Anonymous External Contributor
2022-05-20	reported typo in Terminology note
Modifications
Modification Date	Modifier	Organization
2008-07-01	Eric Dalci	Cigital
2008-07-01	updated Time_of_Introduction
2008-08-15		Veracode
2008-08-15	Suggested OWASP Top Ten 2004 mapping
2008-09-08	CWE Content Team	MITRE
2008-09-08	updated Common_Consequences, Relationships, Other_Notes, Taxonomy_Mappings, Weakness_Ordinalities
2009-05-27	CWE Content Team	MITRE
2009-05-27	updated Demonstrative_Examples, Name
2009-07-27	CWE Content Team	MITRE
2009-07-27	updated Demonstrative_Examples, Description, Name
2009-10-29	CWE Content Team	MITRE
2009-10-29	updated Common_Consequences, Description, Other_Notes, Potential_Mitigations
2010-02-16	CWE Content Team	MITRE
2010-02-16	updated Potential_Mitigations, Relationships
2010-06-21	CWE Content Team	MITRE
2010-06-21	updated Description, Name
2011-03-29	CWE Content Team	MITRE
2011-03-29	updated Demonstrative_Examples
2011-06-01	CWE Content Team	MITRE
2011-06-01	updated Common_Consequences
2012-05-11	CWE Content Team	MITRE
2012-05-11	updated Common_Consequences, Demonstrative_Examples, References, Related_Attack_Patterns, Relationships
2012-10-30	CWE Content Team	MITRE
2012-10-30	updated Potential_Mitigations
2013-02-21	CWE Content Team	MITRE
2013-02-21	updated Relationships
2013-07-17	CWE Content Team	MITRE
2013-07-17	updated Relationships
2014-02-18	CWE Content Team	MITRE
2014-02-18	updated Applicable_Platforms, Demonstrative_Examples, Description, Other_Notes, Terminology_Notes
2014-06-23	CWE Content Team	MITRE
2014-06-23	updated Relationships
2014-07-30	CWE Content Team	MITRE
2014-07-30	updated Relationships, Taxonomy_Mappings
2015-12-07	CWE Content Team	MITRE
2015-12-07	updated Demonstrative_Examples, Relationships
2017-05-03	CWE Content Team	MITRE
2017-05-03	updated Potential_Mitigations, Related_Attack_Patterns, Relationships
2017-11-08	CWE Content Team	MITRE
2017-11-08	updated Causal_Nature, Likelihood_of_Exploit, Modes_of_Introduction, References, Relationships, Taxonomy_Mappings
2018-03-27	CWE Content Team	MITRE
2018-03-27	updated Relationships
2019-01-03	CWE Content Team	MITRE
2019-01-03	updated Taxonomy_Mappings
2019-06-20	CWE Content Team	MITRE
2019-06-20	updated Related_Attack_Patterns, Relationships
2020-02-24	CWE Content Team	MITRE
2020-02-24	updated Potential_Mitigations, References, Relationships
2020-06-25	CWE Content Team	MITRE
2020-06-25	updated Potential_Mitigations
2020-08-20	CWE Content Team	MITRE
2020-08-20	updated Relationships
2020-12-10	CWE Content Team	MITRE
2020-12-10	updated Relationships
2021-03-15	CWE Content Team	MITRE
2021-03-15	updated Relationships
2021-07-20	CWE Content Team	MITRE
2021-07-20	updated Description, Observed_Examples, Relationships
2021-10-28	CWE Content Team	MITRE
2021-10-28	updated Relationships
2022-06-28	CWE Content Team	MITRE
2022-06-28	updated Observed_Examples, Relationships
2022-10-13	CWE Content Team	MITRE
2022-10-13	updated Observed_Examples, References, Terminology_Notes
2023-01-31	CWE Content Team	MITRE
2023-01-31	updated Description, Potential_Mitigations
Previous Entry Names
Change Date	Previous Entry Name
2008-04-11	Command Injection

2009-05-27	Failure to Sanitize Data into a Control Plane (aka 'Command Injection')

2009-07-27	Failure to Sanitize Data into a Control Plane ('Command Injection')

2010-06-21	Improper Sanitization of Special Elements used in a Command ('Command Injection')


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Common Weakness Enumeration

CWE-77: Improper Neutralization of Special Elements used in a Command ('Command Injection')