Subverting Environment Variable Values |
Attack Pattern ID: 13 (Standard Attack Pattern Completeness: Complete) | Typical Severity: Very High | Status: Draft |
Summary
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 Execution Flow
The attacker probes the application for information. Which version of the application is running? Are there known environment variables? etc.
The attacker gains control of an environment variable and ties to find out what process(es) the environment variable controls.
The attacker modifies the environment variable to abuse the normal flow of processes or to gain access to privileged ressources.
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 attemp to manipulate that variable.
Description
Environment variables
Changing the LD_LIBRARY_PATH environment variable in TELNET will cause TELNET to use an alternate (possibly Trojan) version of a function library. The Trojan library must be accessible using the target file system and should include Trojan code that will allow the user to log in with a bad password. This requires that the attacker upload the Trojan library to a specific location on the target.
As an alternative to uploading a Trojan file, some file systems support file paths that include remote addresses, such as \\172.16.2.100\shared_files\trojan_dll.dll.
Related Vulnerabilities
Path Manipulation (CVE-1999-0073)
Skill or Knowledge Level: Low
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/High: Some more advanced attacks may require knowledge about protocols and probing technique which help controling a variable. The malicious user may try to understand the authentication mechanism in order to defeat it.
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.
The attacker may try to obfuscate its attempts to subvert the target process (such as authentication) by using valid values for the variable she controls. By using valid values the user tries to understand the authentication mechanism. This would be in preparation to a more serious attack.
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.
- Run Arbitrary Code
- Privilege Escalation
- Denial of Service
- Information Leakage
The activation zone is the server side function where the client controlled parameter is consumed.
Consuming an attacker contolled parameter can defeat the normal process of the application.
CWE-ID | Weakness Name | Weakness Relationship Type |
---|---|---|
353 | Failure to Add Integrity Check Value | Targeted |
285 | Improper Access Control (Authorization) | Secondary |
302 | Authentication Bypass by Assumed-Immutable Data | Targeted |
74 | Failure to Sanitize Data into a Different Plane ('Injection') | Targeted |
15 | External Control of System or Configuration Setting | Targeted |
73 | External Control of File Name or Path | Targeted |
20 | Improper Input Validation | Secondary |
200 | Information Exposure | Secondary |
Vulnerability ID | Relationship Description |
---|---|
CVE-2006-4244 | SQL-Ledger 2.4.4 through 2.6.17 authenticates users by verifying that the value of the sql-ledger-[username] cookie matches the value of the sessionid parameter, which allows remote attackers to gain access as any logged-in user by setting the cookie and the parameter to the same value. |
CVE-2006-2734 | enter.asp in Mini-Nuke 2.3 and earlier makes it easier for remote attackers to conduct password guessing attacks by setting the guvenlik parameter to the same value as the hidden gguvenlik parameter, which bypasses a verification step because the guvenlik parameter is assumed to be immutable by the attacker. |
CVE-2006-2527 | SecurityDatabase\User\Admin/admin.php in phpBazar 2.1.0 and earlier allows remote attackers to bypass the authentication process and gain unauthorized access to the administrative section by setting the action parameter to edit_member and the value parameter to 1. |
CVE-2006-1505 | base_maintenance.php in Basic Analysis and Security Engine (BASE) before 1.2.4 (melissa), when running in standalone mode, allows remote attackers to bypass authentication, possibly by setting the standalone parameter to "yes". |
Nature | Type | ID | Name | Description | View(s) this relationship pertains to |
---|---|---|---|---|---|
PeerOf | Attack Pattern | 10 | Buffer Overflow via Environment Variables | Mechanism of Attack1000 | |
CanPrecede | Attack Pattern | 14 | Client-side Injection-induced Buffer Overflow | Mechanism of Attack1000 | |
ChildOf | Attack Pattern | 77 | Manipulating User-Controlled Variables | Mechanism of Attack1000 | |
ChildOf | Attack Pattern | 264 | Environment variable manipulation | Mechanism of Attack (primary)1000 | |
ParentOf | Attack Pattern | 38 | Leveraging/Manipulating Configuration File Search Paths | Mechanism of Attack1000 | |
ParentOf | Attack Pattern | 76 | Manipulating Input to File System Calls | Mechanism of Attack1000 |
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.
CWE - Input Validation
Submissions | ||||
---|---|---|---|---|
Submitter | Organization | Date | ||
G. Hoglund and G. McGraw. Exploiting Software: How to Break Code. Addison-Wesley, February 2004. | Cigital, Inc | 2007-03-01 |
Modifications | |||||
---|---|---|---|---|---|
Modifier | Organization | Date | Comments | ||
Eric Dalci | Cigital, Inc | 2007-02-13 | Fleshed out content to CAPEC schema from the original descriptions in "Exploiting Software" | ||
Sean Barnum | Cigital, Inc | 2007-03-05 | Review and revise | ||
Richard Struse | VOXEM, Inc | 2007-03-26 | Review and feedback leading to changes in Name, Description and Related Attack Patterns | ||
Sean Barnum | Cigital, Inc | 2007-04-13 | Modified pattern content according to review and feedback |