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Improper Neutralization of Directives in Statically Saved Code ('Static Code Injection')

Draft Base
Structure: Simple
Description

Static Code Injection occurs when an application incorporates unvalidated or improperly sanitized user input directly into a static, executable resource like a configuration file, template, or library. Because this input is saved and later executed, it allows an attacker to inject malicious code that becomes a permanent part of the application's logic.

Extended Description

This vulnerability is dangerous because the injected code becomes embedded within a file that the system trusts and executes automatically. Unlike attacks that only affect a single transaction, a successful static code injection can persistently compromise the application, leading to ongoing data theft, system takeover, or service disruption every time the compromised resource is used. To prevent it, developers must treat all data destined for static files as untrusted. Implement strict input validation using allowlists for expected values and context-specific output encoding or sanitization before writing data to configuration files, templates, or scripts. Never construct executable code by simply concatenating user input.
Common Consequences 5
Scope: Confidentiality

Impact: Read Files or DirectoriesRead Application Data

The injected code could access restricted data / files.

Scope: Access Control

Impact: Bypass Protection Mechanism

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

Scope: Access Control

Impact: Gain Privileges or Assume Identity

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

Scope: IntegrityConfidentialityAvailabilityOther

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.

Scope: Non-Repudiation

Impact: Hide Activities

Often the actions performed by injected control code are unlogged.
Potential Mitigations 2
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: Implementation

Strategy: Output Encoding

Perform proper output validation and escaping to neutralize all code syntax from data written to code files.
Demonstrative Examples 1

ID : DX-32

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

Code Example:

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

Code Example:

Attack
bash
which will decode to the following:

Code Example:

Attack
bash
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 (Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')) is also possible in this situation.
Observed Examples 5
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.
Applicable Platforms
Languages:
PHP : UndeterminedPerl : UndeterminedInterpreted : Undetermined
Modes of Introduction
Implementation
Implementation
Related Attack Patterns
Affected Resources
  1. File or Directory
Related Weaknesses
ChildOf: Improper Control of Generation of Code ('Code Injection') (CWE-94)
Taxonomy Mapping
  • PLOVER
  • Software Fault Patterns
Notes
Relationship"HTML injection" (see Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting'): XSS) could be thought of as an example of this, but the code is injected and executed on the client side, not the server side. Server-Side Includes (SSI) are an example of direct static code injection.