The product constructs all or part of a code segment using externally-influenced input from an upstream component, but it does not neutralize or incorrectly neutralizes special elements that could modify the syntax or behavior of the intended code segment.

Primary

Resultant

Code Injection

Implementation
REALIZATION: This weakness is caused during implementation of an architectural security tactic.

Medium

Access Control
Bypass Protection Mechanism
In some cases, injectable code controls authentication; this may lead to a remote vulnerability.

Access Control
Gain Privileges or Assume Identity
Injected code can access resources that the attacker is directly prevented from accessing.

Integrity
Confidentiality
Availability
Execute Unauthorized Code or Commands
When a product allows a user's input to contain code syntax, it might be possible for an attacker to craft the code in such a way that it will alter the intended control flow of the product. As a result, code injection can often result in the execution of arbitrary code. Code injection attacks can also lead to loss of data integrity in nearly all cases, since the control-plane data injected is always incidental to data recall or writing.

Non-Repudiation
Hide Activities
Often the actions performed by injected control code are unlogged.

Automated Static Analysis
Automated static analysis, commonly referred to as Static Application Security Testing (SAST), can find some instances of this weakness by analyzing source code (or binary/compiled code) without having to execute it. Typically, this is done by building a model of data flow and control flow, then searching for potentially-vulnerable patterns that connect "sources" (origins of input) with "sinks" (destinations where the data interacts with external components, a lower layer such as the OS, etc.)
High

Architecture and Design
Refactor your program so that you do not have to dynamically generate code.

Architecture and Design

Run your code in a "jail" or similar sandbox environment that enforces strict boundaries between the process and the operating system. This may effectively restrict which code can be executed by your product.
Examples include the Unix chroot jail and AppArmor. In general, managed code may provide some protection.
This may not be a feasible solution, and it only limits the impact to the operating system; the rest of your application may still be subject to compromise.
Be careful to avoid CWE-243 and other weaknesses related to jails.

Implementation
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.
To reduce the likelihood of code injection, use stringent allowlists that limit which constructs are allowed. If you are dynamically constructing code that invokes a function, then verifying that the input is alphanumeric might be insufficient. An attacker might still be able to reference a dangerous function that you did not intend to allow, such as system(), exec(), or exit().

Testing
Use automated static analysis tools that target this type of weakness. Many modern techniques use data flow analysis to minimize the number of false positives. This is not a perfect solution, since 100% accuracy and coverage are not feasible.

Testing
Use dynamic tools and techniques that interact with the product using large test suites with many diverse inputs, such as fuzz testing (fuzzing), robustness testing, and fault injection. The product's operation may slow down, but it should not become unstable, crash, or generate incorrect results.

Operation
Compilation or Build Hardening
Run the code in an environment that performs automatic taint propagation and prevents any command execution that uses tainted variables, such as Perl's "-T" switch. This will force the program to perform validation steps that remove the taint, although you must be careful to correctly validate your inputs so that you do not accidentally mark dangerous inputs as untainted (see CWE-183 and CWE-184).

Operation
Environment Hardening
Run the code in an environment that performs automatic taint propagation and prevents any command execution that uses tainted variables, such as Perl's "-T" switch. This will force the program to perform validation steps that remove the taint, although you must be careful to correctly validate your inputs so that you do not accidentally mark dangerous inputs as untainted (see CWE-183 and CWE-184).

Implementation

For Python programs, it is frequently encouraged to use the ast.literal_eval() function instead of eval, since it is intentionally designed to avoid executing code. However, an adversary could still cause excessive memory or stack consumption via deeply nested structures [REF-1372], so the python documentation discourages use of ast.literal_eval() on untrusted data [REF-1373].

Discouraged Common Practice

This example attempts to write user messages to a message file and allow users to view them.

$MessageFile = "messages.out";if ($_GET["action"] == "NewMessage") {$name = $_GET["name"];$message = $_GET["message"];$handle = fopen($MessageFile, "a+");fwrite($handle, "<b>$name</b> says '$message'<hr>\n");fclose($handle);echo "Message Saved!<p>\n";}else if ($_GET["action"] == "ViewMessages") {include($MessageFile);}

While the programmer intends for the MessageFile to only include data, an attacker can provide a message such as:

name=h4x0rmessage=%3C?php%20system(%22/bin/ls%20-l%22);?%3E

which will decode to the following:

<?php system("/bin/ls -l");?>

The programmer thought they were just including the contents of a regular data file, but PHP parsed it and executed the code. Now, this code is executed any time people view messages.
Notice that XSS (CWE-79) is also possible in this situation.

edit-config.pl: This CGI script is used to modify settings in a configuration file.

use CGI qw(:standard);
sub config_file_add_key {
my ($fname, $key, $arg) = @_;

# code to add a field/key to a file goes here

}
sub config_file_set_key {
my ($fname, $key, $arg) = @_;

# code to set key to a particular file goes here

}
sub config_file_delete_key {
my ($fname, $key, $arg) = @_;

# code to delete key from a particular file goes here

}
sub handleConfigAction {
my ($fname, $action) = @_;my $key = param('key');my $val = param('val');

# this is super-efficient code, especially if you have to invoke

# any one of dozens of different functions!

my $code = "config_file_$action_key(\$fname, \$key, \$val);";eval($code);
}
$configfile = "/home/cwe/config.txt";print header;if (defined(param('action'))) {handleConfigAction($configfile, param('action'));}else {print "No action specified!\n";}

The script intends to take the 'action' parameter and invoke one of a variety of functions based on the value of that parameter - config_file_add_key(), config_file_set_key(), or config_file_delete_key(). It could set up a conditional to invoke each function separately, but eval() is a powerful way of doing the same thing in fewer lines of code, especially when a large number of functions or variables are involved. Unfortunately, in this case, the attacker can provide other values in the action parameter, such as:

add_key(",","); system("/bin/ls");

This would produce the following string in handleConfigAction():

config_file_add_key(",","); system("/bin/ls");

Any arbitrary Perl code could be added after the attacker has "closed off" the construction of the original function call, in order to prevent parsing errors from causing the malicious eval() to fail before the attacker's payload is activated. This particular manipulation would fail after the system() call, because the "_key(\$fname, \$key, \$val)" portion of the string would cause an error, but this is irrelevant to the attack because the payload has already been activated.

This simple python3 script asks a user to supply a comma-separated list of numbers as input and adds them together.

def main():

sum = 0
try:

numbers = eval(input("Enter a comma-separated list of numbers: "))

except SyntaxError:

print("Error: invalid input")
return

for num in numbers:

sum = sum + num

print(f"Sum of {numbers} = {sum}")

main()

The eval() function can take the user-supplied list and convert it into a Python list object, therefore allowing the programmer to use list comprehension methods to work with the data. However, if code is supplied to the eval() function, it will execute that code. For example, a malicious user could supply the following string:

__import__('subprocess').getoutput('rm -r *')

This would delete all the files in the current directory. For this reason, it is not recommended to use eval() with untrusted input.
A way to accomplish this without the use of eval() is to apply an integer conversion on the input within a try/except block. If the user-supplied input is not numeric, this will raise a ValueError. By avoiding eval(), there is no opportunity for the input string to be executed as code.

def main():

sum = 0
numbers = input("Enter a comma-separated list of numbers: ").split(",")
try:

for num in numbers:

sum = sum + int(num)

print(f"Sum of {numbers} = {sum}")

except ValueError:

print("Error: invalid input")

main()

An alternative, commonly-cited mitigation for this kind of weakness is to use the ast.literal_eval() function, since it is intentionally designed to avoid executing code. However, an adversary could still cause excessive memory or stack consumption via deeply nested structures [REF-1372], so the python documentation discourages use of ast.literal_eval() on untrusted data [REF-1373].

The following code is a workflow job written
using YAML. The code attempts to download pull request
artifacts, unzip from the artifact called pr.zip and
extract the value of the file NR into a variable
"pr_number" that will be used later in another job. It
attempts to create a github workflow environment
variable, writing to $GITHUB_ENV. The environment
variable value is retrieved from an external
resource.

name: Deploy Preview
jobs:

deploy:

runs-on: ubuntu-latest
steps:

- name: 'Download artifact'
uses: actions/github-script
with:

script: |

var artifacts = await github.actions.listWorkflowRunArtifacts({

owner: context.repo.owner,
repo: context.repo.repo,
run_id: ${{ github.event.workflow_run.id }},

});
var matchPrArtifact = artifacts.data.artifacts.filter((artifact) => {

return artifact.name == "pr"

})[0];
var downloadPr = await github.actions.downloadArtifact({

owner: context.repo.owner,
repo: context.repo.repo,
artifact_id: matchPrArtifact.id,
archive_format: 'zip',

});
var fs = require('fs');
fs.writeFileSync('${{github.workspace}}/pr.zip', Buffer.from(downloadPr.data));

- run: |

unzip pr.zip
echo "pr_number=$(cat NR)" >> $GITHUB_ENV

The code does not neutralize the value of the
file NR, e.g. by validating that NR only contains a
number (CWE-1284). The NR file is attacker controlled
because it originates from a pull request that produced
pr.zip.
The attacker could escape the existing
pr_number and create a new variable using a "\n"
(CWE-93) followed by any environment variable to be
added such as:

\nNODE_OPTIONS="--experimental-modules --experiments-loader=data:text/javascript,console.log('injected code');//"

This would result in injecting and running
javascript code (CWE-94) on the workflow runner with
elevated privileges.

The code could be modified to validate that the NR
file only contains a numeric value, or the code could
retrieve the PR number from a more trusted source.

CVE-2023-29374
Math component in an LLM framework translates user input into a Python
expression that is input into the Python exec() method, allowing code
execution - one variant of a "prompt injection" attack.
https://www.cve.org/CVERecord?id=CVE-2023-29374

CVE-2024-5565
Python-based library uses an LLM prompt containing user input to
dynamically generate code that is then fed as input into the Python
exec() method, allowing code execution - one variant of a "prompt
injection" attack.
https://www.cve.org/CVERecord?id=CVE-2024-5565

CVE-2024-4181
Framework for LLM applications allows eval injection via a crafted response from a hosting provider.
https://www.cve.org/CVERecord?id=CVE-2024-4181

CVE-2022-2054
Python compiler uses eval() to execute malicious strings as Python code.
https://www.cve.org/CVERecord?id=CVE-2022-2054

CVE-2021-22204
Chain: regex in EXIF processor code does not correctly determine where a string ends (CWE-625), enabling eval injection (CWE-95), as exploited in the wild per CISA KEV.
https://www.cve.org/CVERecord?id=CVE-2021-22204

CVE-2020-8218
"Code injection" in VPN product, as exploited in the wild per CISA KEV.
https://www.cve.org/CVERecord?id=CVE-2020-8218

CVE-2008-5071
Eval injection in PHP program.
https://www.cve.org/CVERecord?id=CVE-2008-5071

CVE-2002-1750
Eval injection in Perl program.
https://www.cve.org/CVERecord?id=CVE-2002-1750

CVE-2008-5305
Eval injection in Perl program using an ID that should only contain hyphens and numbers.
https://www.cve.org/CVERecord?id=CVE-2008-5305

CVE-2002-1752
Direct code injection into Perl eval function.
https://www.cve.org/CVERecord?id=CVE-2002-1752

CVE-2002-1753
Eval injection in Perl program.
https://www.cve.org/CVERecord?id=CVE-2002-1753

CVE-2005-1527
Direct code injection into Perl eval function.
https://www.cve.org/CVERecord?id=CVE-2005-1527

CVE-2005-2837
Direct code injection into Perl eval function.
https://www.cve.org/CVERecord?id=CVE-2005-2837

CVE-2005-1921
MFV. code injection into PHP eval statement using nested constructs that should not be nested.
https://www.cve.org/CVERecord?id=CVE-2005-1921

CVE-2005-2498
MFV. code injection into PHP eval statement using nested constructs that should not be nested.
https://www.cve.org/CVERecord?id=CVE-2005-2498

CVE-2005-3302
Code injection into Python eval statement from a field in a formatted file.
https://www.cve.org/CVERecord?id=CVE-2005-3302

CVE-2007-1253
Eval injection in Python program.
https://www.cve.org/CVERecord?id=CVE-2007-1253

CVE-2001-1471
chain: Resultant eval injection. An invalid value prevents initialization of variables, which can be modified by attacker and later injected into PHP eval statement.
https://www.cve.org/CVERecord?id=CVE-2001-1471

CVE-2002-0495
Perl code directly injected into CGI library file from parameters to another CGI program.
https://www.cve.org/CVERecord?id=CVE-2002-0495

CVE-2005-1876
Direct PHP code injection into supporting template file.
https://www.cve.org/CVERecord?id=CVE-2005-1876

CVE-2005-1894
Direct code injection into PHP script that can be accessed by attacker.
https://www.cve.org/CVERecord?id=CVE-2005-1894

CVE-2003-0395
PHP code from User-Agent HTTP header directly inserted into log file implemented as PHP script.
https://www.cve.org/CVERecord?id=CVE-2003-0395

CODE
Code Evaluation and Injection

Part 4-2
Req CR 3.5

Part 3-3
Req SR 3.5

Part 4-1
Req SVV-1

Part 4-1
Req SVV-3

Allowed-with-Review
This entry is frequently misused for vulnerabilities with a technical impact of "code execution," which does not by itself indicate a root cause weakness, since dozens of weaknesses can enable code execution.
This weakness only applies when the product's functionality intentionally constructs all or part of a code segment. It could be that executing code could be the result of other weaknesses that do not involve the construction of code segments.

Injection problems encompass a wide variety of issues -- all mitigated in very different ways. For this reason, the most effective way to discuss these weaknesses is to note the distinct features that classify them as injection weaknesses. The most important issue to note is that all injection problems share one thing in common -- i.e., they allow for the injection of control plane data into the user-controlled data plane. This means that the execution of the process may be altered by sending code in through legitimate data channels, using no other mechanism. While buffer overflows, and many other flaws, involve the use of some further issue to gain execution, injection problems need only for the data to be parsed. The most classic instantiations of this category of weakness are SQL injection and format string vulnerabilities.

PLOVER
2006-07-19
Draft 3
2006-07-19

Eric Dalci
Cigital
2008-07-01
updated Time_of_Introduction

CWE Content Team
MITRE
2008-09-08
updated Applicable_Platforms, Relationships, Research_Gaps, Taxonomy_Mappings

CWE Content Team
MITRE
2009-01-12
updated Common_Consequences, Demonstrative_Examples, Description, Likelihood_of_Exploit, Name, Potential_Mitigations, Relationships

CWE Content Team
MITRE
2009-03-10
updated Potential_Mitigations

CWE Content Team
MITRE
2009-05-27
updated Demonstrative_Examples, Name

CWE Content Team
MITRE
2010-02-16
updated Potential_Mitigations

CWE Content Team
MITRE
2010-06-21
updated Description, Potential_Mitigations

CWE Content Team
MITRE
2011-03-29
updated Name

CWE Content Team
MITRE
2011-06-01
updated Common_Consequences

CWE Content Team
MITRE
2012-05-11
updated Common_Consequences, Demonstrative_Examples, Observed_Examples, References, Relationships

CWE Content Team
MITRE
2012-10-30
updated Potential_Mitigations

CWE Content Team
MITRE
2013-02-21
updated Relationships

CWE Content Team
MITRE
2014-07-30
updated Relationships

CWE Content Team
MITRE
2015-12-07
updated Relationships

CWE Content Team
MITRE
2017-11-08
updated Demonstrative_Examples, Modes_of_Introduction, Relationships

CWE Content Team
MITRE
2019-06-20
updated Related_Attack_Patterns, Type

CWE Content Team
MITRE
2019-09-19
updated Relationships

CWE Content Team
MITRE
2020-02-24
updated Potential_Mitigations, Relationships

CWE Content Team
MITRE
2020-06-25
updated Potential_Mitigations

CWE Content Team
MITRE
2020-08-20
updated Relationships

CWE Content Team
MITRE
2021-03-15
updated Demonstrative_Examples

CWE Content Team
MITRE
2021-07-20
updated Relationships

CWE Content Team
MITRE
2021-10-28
updated Relationships

CWE Content Team
MITRE
2022-04-28
updated Research_Gaps

CWE Content Team
MITRE
2022-06-28
updated Observed_Examples, Relationships

CWE Content Team
MITRE
2022-10-13
updated Observed_Examples

CWE Content Team
MITRE
2023-01-31
updated Demonstrative_Examples, Description, Potential_Mitigations, Relationships

CWE Content Team
MITRE
2023-04-27
updated Demonstrative_Examples, Detection_Factors, Relationships, Time_of_Introduction

CWE Content Team
MITRE
2023-06-29
updated Mapping_Notes, Relationships, Taxonomy_Mappings

CWE Content Team
MITRE
2024-02-29
4.14
2024-02-29
updated Demonstrative_Examples, Potential_Mitigations, References

CWE Content Team
MITRE
2024-07-16
4.15
2024-07-16
updated Applicable_Platforms, Observed_Examples

CWE Content Team
MITRE
2024-11-19
4.16
2024-11-19
updated Mapping_Notes, Relationships

CWE Content Team
MITRE
2025-04-03
4.17
2025-04-03
updated Alternate_Terms, Common_Consequences, Description, Diagram, Theoretical_Notes

CWE Content Team
MITRE
2025-12-11
4.19
2025-12-11
updated Demonstrative_Examples, Relationships, Weakness_Ordinalities

"Mapping CWE to 62443" Sub-Working Group
CWE-CAPEC ICS/OT SIG
2023-06-29
4.12
2023-06-29
Suggested mappings to ISA/IEC 62443.

Abhi Balakrishnan
2024-02-29
4.17
2025-04-03
Contributed usability diagram concepts used by the CWE team.

Matthew A. Pagan
Spectrum
2025-08-22
4.19
2025-12-11
Discovered a syntax issue in the Python3 demox (DX-156) and suggested a fix

Code Injection
Failure to Control Generation of Code (aka 'Code Injection')
Failure to Control Generation of Code ('Code Injection')