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CWE-96: Improper Neutralization of Directives in Statically Saved Code ('Static Code Injection')

 
Improper Neutralization of Directives in Statically Saved Code ('Static Code Injection')
Weakness ID: 96 (Weakness Base)Status: Draft
+ Description

Description Summary

The software receives input from an upstream component, but it does not neutralize or incorrectly neutralizes code syntax before inserting the input into an executable resource, such as a library, configuration file, or template.
+ Time of Introduction
  • Architecture and Design
  • Implementation
+ Applicable Platforms

Languages

PHP

Perl

All Interpreted Languages

+ Common Consequences
ScopeEffect
Confidentiality

Technical Impact: Read files or directories; Read application data

The injected code could access restricted data / files.

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 / assume identity

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

Integrity
Confidentiality
Availability
Other

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.

+ 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 
$MessageFile = "cwe-94/messages.out";
if ($_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:

(Attack)
 
name=h4x0r
message=%3C?php%20system(%22/bin/ls%20-l%22);?%3E

which will decode to the following:

(Attack)
 
<?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.

+ Observed Examples
ReferenceDescription
CVE-2002-0495Perl code directly injected into CGI library file from parameters to another CGI program.
CVE-2005-1876Direct PHP code injection into supporting template file.
CVE-2005-1894Direct code injection into PHP script that can be accessed by attacker.
CVE-2003-0395PHP code from User-Agent HTTP header directly inserted into log file implemented as PHP script.
CVE-2007-6652chain: execution after redirect allows non-administrator to perform static code injection.
+ Potential Mitigations

Phase: Implementation

Strategy: Input Validation

Assume all input is malicious. Use an "accept known good" input validation strategy, i.e., use a whitelist 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 (i.e., do not rely on a blacklist). A blacklist 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, blacklists can be useful for detecting potential attacks or determining which inputs are so malformed that they should be rejected outright.

Phase: Implementation

Strategy: Output Encoding

Perform proper output validation and escaping to neutralize all code syntax from data written to code files.

+ Other Notes

"HTML injection" (see XSS) could be thought of as an example of this, but it is executed on the client side, not the server side. Server-Side Includes (SSI) are an example of direct static code injection.

This issue is most frequently found in PHP applications that allow users to set configuration variables that are stored within executable php files. Technically, this could also be performed in some compiled code (e.g. by byte-patching an executable), although it is highly unlikely.

+ Weakness Ordinalities
OrdinalityDescription
Primary
(where the weakness exists independent of other weaknesses)
+ Relationships
NatureTypeIDNameView(s) this relationship pertains toView(s)
ChildOfWeakness ClassWeakness Class94Improper Control of Generation of Code ('Code Injection')
Development Concepts (primary)699
Research Concepts (primary)1000
ChildOfCategoryCategory632Weaknesses that Affect Files or Directories
Resource-specific Weaknesses (primary)631
ChildOfCategoryCategory896SFP Cluster: Tainted Input
Software Fault Pattern (SFP) Clusters (primary)888
ParentOfWeakness VariantWeakness Variant97Improper Neutralization of Server-Side Includes (SSI) Within a Web Page
Development Concepts (primary)699
Research Concepts (primary)1000
MemberOfViewView884CWE Cross-section
CWE Cross-section (primary)884
+ Affected Resources
  • File/Directory
+ Causal Nature

Explicit

+ Taxonomy Mappings
Mapped Taxonomy NameNode IDFitMapped Node Name
PLOVERDirect Static Code Injection
+ Content History
Submissions
Submission DateSubmitterOrganizationSource
PLOVERExternally Mined
Modifications
Modification DateModifierOrganizationSource
2008-07-01Eric DalciCigitalExternal
updated Potential_Mitigations, Time_of_Introduction
2008-09-08CWE Content TeamMITREInternal
updated Applicable_Platforms, Relationships, Other_Notes, Taxonomy_Mappings, Weakness_Ordinalities
2009-05-27CWE Content TeamMITREInternal
updated Description, Name
2010-04-05CWE Content TeamMITREInternal
updated Description, Name
2010-06-21CWE Content TeamMITREInternal
updated Potential_Mitigations
2011-06-01CWE Content TeamMITREInternal
updated Common_Consequences
2012-05-11CWE Content TeamMITREInternal
updated Common_Consequences, Demonstrative_Examples, Relationships
2012-10-30CWE Content TeamMITREInternal
updated Potential_Mitigations
2013-02-21CWE Content TeamMITREInternal
updated Observed_Examples
Previous Entry Names
Change DatePrevious Entry Name
2008-04-11Direct Static Code Injection
2009-05-27Insufficient Control of Directives in Statically Saved Code (Static Code Injection)
2010-04-05Improper Sanitization of Directives in Statically Saved Code ('Static Code Injection')
Page Last Updated: February 18, 2014