Improper Neutralization of Special Elements used in an Expression Language Statement ('Expression Language Injection')

Opis

The product constructs all or part of an expression language (EL) statement in a framework such as a Java Server Page (JSP) using externally-influenced input from an upstream component, but it does not neutralize or incorrectly neutralizes special elements that could modify the intended EL statement before it is executed.

Frameworks such as Java Server Page (JSP) allow a developer to insert executable expressions within otherwise-static content. When the developer is not aware of the executable nature of these expressions and/or does not disable them, then if an attacker can inject expressions, this could lead to code execution or other unexpected behaviors.

Inne nazwy

EL Injection

Skutki

• Confidentiality

  Read Application Data

• Integrity

  Execute Unauthorized Code or Commands

Zapobieganie

• Architecture and Design

  Avoid adding user-controlled data into an expression interpreter when possible.

• Implementation

  If user-controlled data must be added to an expression interpreter, one or more of the following should be performed:

  - Validate that the user input will not evaluate as an expression

  - Encode the user input in a way that ensures it is not evaluated as an expression

• System Configuration, Operation

  The framework or tooling might allow the developer to disable or deactivate the processing of EL expressions, such as setting the isELIgnored attribute for a JSP page to "true".

Przykłady podatności

• CVE-2021-44228 Product does not neutralize ${xyz} style expressions, allowing remote code execution. (log4shell vulnerability in log4j)

Słabość nadrzędna

• CWE-77 Improper Neutralization of Special Elements used in a Command ('Command Injection')
• CWE-74 Improper Neutralization of Special Elements in Output Used by a Downstream Component ('Injection')

Pokrewna

• CWE-1336 Improper Neutralization of Special Elements Used in a Template Engine

Kiedy powstaje

• Architecture and Design
• Implementation

Dotyczy

Java

Uwagi

The interrelationships and differences between CWE-917 and CWE-1336 need to be further clarified.

In certain versions of Spring 3.0.5 and earlier, there was a vulnerability (CVE-2011-2730) in which Expression Language tags would be evaluated twice, which effectively exposed any application to EL injection. However, even for later versions, this weakness is still possible depending on configuration.

Źródła

1. Expression Language Injection — Stefano Di Paola, Arshan Dabirsiaghi, 2011
2. Remote Code with Expression Language Injection — Dan Amodio, 2012
3. Neutralizing Your Inputs: A Log4Shell Weakness Story — CWE/CAPEC
4. Expression Language Injection — OWASP