CAPEC-13 - Subverting Environment Variable Values

The attacker directly or indirectly modifies environment variables used by or controlling the target software. The attacker's goal is to cause the target software to deviate from its expected operation in a manner that benefits the attacker.






  • Attack Methods 3
  • Injection
  • Modification of Resources
  • Protocol Manipulation
  • Purposes 1
  • Penetration
  • Sec Principles 1
  • Reluctance to trust
  • Scopes 4
  • Execute unauthorized code or commands
  • Availability
  • Integrity
  • Confidentiality
  • Bypass protection mechanism
  • Authorization
  • Access_Control
  • Confidentiality
  • Unexpected State
  • Availability
  • Read application data
  • Confidentiality

Low level: In a web based scenario, the client controls the data that it submitted to the server. So anybody can try to send malicious data and try to bypass the authentication mechanism.

Medium level: Some more advanced attacks may require knowledge about protocols and probing technique which help controlling a variable. The malicious user may try to understand the authentication mechanism in order to defeat it.

An environment variable is accessible to the user.

An environment variable used by the application can be tainted with user supplied data.

Input data used in an environment variable is not validated properly.

The variables encapsulation is not done properly. For instance setting a variable as public in a class makes it visible and an attacker may attempt to manipulate that variable.

An attacker can intentionally modify the client side parameter and monitor how the server behaves in response to that modification. For instance an attacker will look at the cookie data, the URL parameters, the hidden variables in forms, variables used in system calls, etc.

If the client uses a program in binary format to connect to the server, disassembler can be used to identify parameter within the binary code, and then the attacker would try to simulate the client application and change some of the parameters sent to the server. For instance the attacker may find that a secret key or a path is hard coded in the binary client application.

Environment variables are frequently stored in cleartext configuration files. If the attacker can modify those configuration files, he can control the environment variables. Even a read access can potentially be dangerous since this may give sensitive information to perform this type of attack. Indeed knowing which environment variables the application uses is a prerequisite to this type of attack.

Always perform wise data validation. Do not accept tainted data without validation. Do not simply base authentication on the client controlled parameter.

Avoid relying on client side validation only.

Step 1 -

The attacker probes the application for information. Which version of the application is running? Are there known environment variables? etc..

Step 1 -

The attacker gains control of an environment variable and ties to find out what process(es) the environment variable controls..

Step 1 -

The attacker modifies the environment variable to abuse the normal flow of processes or to gain access to privileged resources..

Protect environment variables against unauthorized read and write access.

Protect the configuration files which contain environment variables against illegitimate read and write access.

Assume all input is malicious. Create a white list that defines all valid input to the software system based on the requirements specifications. Input that does not match against the white list should not be permitted to enter into the system.

Apply the least privilege principles. If a process has no legitimate reason to read an environment variable do not give that privilege.