CVE-2022-34625: CWE-94: Improper Control of Generation of Code ('Code Injection') (4.8)

Weakness ID: 94

Abstraction: Base
Structure: Simple

Description

The software 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.

Extended Description

When software 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 software. Such an alteration could lead to arbitrary code execution.

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 which 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.

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

Pillar - a weakness that is the most abstract type of weakness and represents a theme for all class/base/variant weaknesses related to it. A Pillar is different from a Category as a Pillar is still technically a type of weakness that describes a mistake, while a Category represents a common characteristic used to group related things.

691

Insufficient Control Flow Management

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.

913

Improper Control of Dynamically-Managed Code Resources

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

Variant - a weakness that is linked to a certain type of product, typically involving a specific language or technology. More specific than a Base weakness. Variant level weaknesses typically describe issues in terms of 3 to 5 of the following dimensions: behavior, property, technology, language, and resource.

95

Improper Neutralization of Directives in Dynamically Evaluated Code (‘Eval 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.

96

Improper Neutralization of Directives in Statically Saved Code (‘Static Code 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.

1336

Improper Neutralization of Special Elements Used in a Template Engine

CanFollow

Variant - a weakness that is linked to a certain type of product, typically involving a specific language or technology. More specific than a Base weakness. Variant level weaknesses typically describe issues in terms of 3 to 5 of the following dimensions: behavior, property, technology, language, and resource.

98

Improper Control of Filename for Include/Require Statement in PHP Program (‘PHP Remote File Inclusion’)

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 “Software Development” (CWE-699)

Nature

Type

ID

Name

MemberOf

Category - a CWE entry that contains a set of other entries that share a common characteristic.

137

Data Neutralization Issues

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 “Weaknesses for Simplified Mapping of Published Vulnerabilities” (CWE-1003)

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 “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

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: Interpreted (Sometimes Prevalent)

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

Access Control

Technical Impact: Bypass Protection Mechanism

In some cases, injectable code controls authentication; this may lead to a remote vulnerability.

Access Control

Technical Impact: Gain Privileges or Assume Identity

Injected code can access resources that the attacker is directly prevented from accessing.

Integrity
Confidentiality
Availability

Technical Impact: 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.

Non-Repudiation

Technical Impact: Hide Activities

Often the actions performed by injected control code are unlogged.

Likelihood Of Exploit

Demonstrative Examples

Example 1

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

(bad code)

Example Language: PHP

$MessageFile = "messages.out";
if ($_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=h4x0r
message=%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.

Example 2

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

(bad code)

Example Language: Perl

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.

Observed Examples

Reference

Description

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.

CVE-2020-8218

“Code injection” in VPN product, as exploited in the wild per CISA KEV.

CVE-2008-5071

Eval injection in PHP program.

CVE-2002-1750

Eval injection in Perl program.

CVE-2008-5305

Eval injection in Perl program using an ID that should only contain hyphens and numbers.

CVE-2002-1752

Direct code injection into Perl eval function.

CVE-2002-1753

Eval injection in Perl program.

CVE-2005-1527

Direct code injection into Perl eval function.

CVE-2005-2837

Direct code injection into Perl eval function.

CVE-2005-1921

MFV. code injection into PHP eval statement using nested constructs that should not be nested.

CVE-2005-2498

MFV. code injection into PHP eval statement using nested constructs that should not be nested.

CVE-2005-3302

Code injection into Python eval statement from a field in a formatted file.

CVE-2007-1253

Eval injection in Python program.

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.

CVE-2002-0495

Perl code directly injected into CGI library file from parameters to another CGI program.

CVE-2005-1876

Direct PHP code injection into supporting template file.

CVE-2005-1894

Direct code injection into PHP script that can be accessed by attacker.

CVE-2003-0395

PHP code from User-Agent HTTP header directly inserted into log file implemented as PHP script.

Potential Mitigations

Phase: Architecture and Design

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

Phase: 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 software.

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.

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.

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().

Phase: 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.

Phase: Testing

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

Phase: Operation

Strategy: 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).

Phase: Operation

Strategy: 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).

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.

Taxonomy Mappings

Mapped Taxonomy Name

Node ID

Fit

Mapped Node Name

PLOVER

CODE

Code Evaluation and Injection

References

[REF-44] Michael Howard, David LeBlanc and John Viega. "24 Deadly Sins of Software Security". “Sin 3: Web-Client Related Vulnerabilities (XSS).” Page 63. McGraw-Hill. 2010.

Content History

Submissions

Submission Date

Submitter

Organization

2006-07-19

PLOVER

Modifications

Modification Date

Modifier

Organization

2008-07-01

Eric Dalci

Cigital

updated Time_of_Introduction

2008-09-08

CWE Content Team

MITRE

updated Applicable_Platforms, Relationships, Research_Gaps, Taxonomy_Mappings

2009-01-12

CWE Content Team

MITRE

updated Common_Consequences, Demonstrative_Examples, Description, Likelihood_of_Exploit, Name, Potential_Mitigations, Relationships

2009-03-10

CWE Content Team

MITRE

updated Potential_Mitigations

2009-05-27

CWE Content Team

MITRE

updated Demonstrative_Examples, Name

2010-02-16

CWE Content Team

MITRE

updated Potential_Mitigations

2010-06-21

CWE Content Team

MITRE

updated Description, Potential_Mitigations

2011-03-29

CWE Content Team

MITRE

updated Name

2011-06-01

CWE Content Team

MITRE

updated Common_Consequences

2012-05-11

CWE Content Team

MITRE

updated Common_Consequences, Demonstrative_Examples, Observed_Examples, References, Relationships

2012-10-30

CWE Content Team

MITRE

updated Potential_Mitigations

2013-02-21

CWE Content Team

MITRE

updated Relationships

2014-07-30

CWE Content Team

MITRE

updated Relationships

2015-12-07

CWE Content Team

MITRE

updated Relationships

2017-11-08

CWE Content Team

MITRE

updated Demonstrative_Examples, Modes_of_Introduction, Relationships

2019-06-20

CWE Content Team

MITRE

updated Related_Attack_Patterns, Type

2019-09-19

CWE Content Team

MITRE

updated Relationships

2020-02-24

CWE Content Team

MITRE

updated Potential_Mitigations, Relationships

2020-06-25

CWE Content Team

MITRE

updated Potential_Mitigations

2020-08-20

CWE Content Team

MITRE

updated Relationships

2021-03-15

CWE Content Team

MITRE

updated Demonstrative_Examples

2021-07-20

CWE Content Team

MITRE

updated Relationships

2021-10-28

CWE Content Team

MITRE

updated Relationships

2022-04-28

CWE Content Team

MITRE

updated Research_Gaps

2022-06-28

CWE Content Team

MITRE

updated Observed_Examples, Relationships

Previous Entry Names

Change Date

Previous Entry Name

2009-01-12

Code Injection

2009-05-27

Failure to Control Generation of Code (aka ‘Code Injection’)

2011-03-29

Failure to Control Generation of Code (‘Code Injection’)

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