The product receives input from an upstream component, but it does not neutralize or incorrectly neutralizes code syntax before using the input in a dynamic evaluation call (e.g. "eval").

Primary

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

Implementation
This weakness is prevalent in handler/dispatch procedures that might want to invoke a large number of functions, or set a large number of variables.

Medium

Confidentiality
Read Files or Directories
Read Application Data
The injected code could access restricted data / files.

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
Other
Execute Unauthorized Code or Commands
Code injection attacks can lead to loss of data integrity in nearly all cases as the control-plane data injected is always incidental to data recall or writing. Additionally, code injection can often result in the execution of arbitrary code or at least modify what code can be executed.

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
Implementation
If possible, refactor your code so that it does not need to use eval() at all.

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.

Implementation

Inputs should be decoded and canonicalized to the application's current internal representation before being validated (CWE-180, CWE-181). Make sure that your application does not inadvertently decode the same input twice (CWE-174). Such errors could be used to bypass allowlist schemes by introducing dangerous inputs after they have been checked. Use libraries such as the OWASP ESAPI Canonicalization control.
Consider performing repeated canonicalization until your input does not change any more. This will avoid double-decoding and similar scenarios, but it might inadvertently modify inputs that are allowed to contain properly-encoded dangerous content.

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

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].

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-2021-22205
Chain: backslash followed by a newline can bypass a validation step (CWE-20), leading to eval injection (CWE-95), as exploited in the wild per CISA KEV.
https://www.cve.org/CVERecord?id=CVE-2021-22205

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-2007-2713
Chain: Execution after redirect triggers eval injection.
https://www.cve.org/CVERecord?id=CVE-2007-2713

Direct Dynamic Code Evaluation ('Eval Injection')

A3
Malicious File Execution
CWE More Specific

A6
Injection Flaws
CWE More Specific

SFP24
Tainted input to command

IDS35-PL
Do not invoke the eval form with a string argument
Exact

Allowed
This CWE entry is at the Variant level of abstraction, which is a preferred level of abstraction for mapping to the root causes of vulnerabilities.
Carefully read both the name and description to ensure that this mapping is an appropriate fit. Do not try to 'force' a mapping to a lower-level Base/Variant simply to comply with this preferred level of abstraction.

Factors: special character errors can play a role in increasing the variety of code that can be injected, although some vulnerabilities do not require special characters at all, e.g. when a single function without arguments can be referenced and a terminator character is not necessary.

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

Eric Dalci
Cigital
2008-07-01
updated Time_of_Introduction

Veracode
2008-08-15
Suggested OWASP Top Ten 2004 mapping

CWE Content Team
MITRE
2008-09-08
updated Applicable_Platforms, Description, Modes_of_Introduction, Relationships, Other_Notes, Taxonomy_Mappings, Weakness_Ordinalities

CWE Content Team
MITRE
2009-01-12
updated Description, Observed_Examples, Other_Notes, Research_Gaps

CWE Content Team
MITRE
2009-05-27
updated Alternate_Terms, Applicable_Platforms, Demonstrative_Examples, Description, Name, References

CWE Content Team
MITRE
2010-02-16
updated Potential_Mitigations

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

CWE Content Team
MITRE
2011-06-01
updated Common_Consequences

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

CWE Content Team
MITRE
2012-10-30
updated Potential_Mitigations

CWE Content Team
MITRE
2013-02-21
updated Observed_Examples

CWE Content Team
MITRE
2014-07-30
updated Relationships, Taxonomy_Mappings

CWE Content Team
MITRE
2017-11-08
updated Causal_Nature, Modes_of_Introduction, References, Relationships, Taxonomy_Mappings

CWE Content Team
MITRE
2019-01-03
updated Taxonomy_Mappings

CWE Content Team
MITRE
2019-06-20
updated Type

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
2021-03-15
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

CWE Content Team
MITRE
2022-10-13
updated Observed_Examples

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

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

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
2025-04-03
4.17
2025-04-03
updated Common_Consequences, Description, Diagram

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

Direct Dynamic Code Evaluation ('Eval Injection')
Insufficient Control of Directives in Dynamically Evaluated Code (aka 'Eval Injection')
Improper Sanitization of Directives in Dynamically Evaluated Code ('Eval Injection')