Description
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.
Potential Impact
Confidentiality
Read Application Data
Integrity
Execute Unauthorized Code or Commands
Mitigations & Prevention
Avoid adding user-controlled data into an expression interpreter when possible.
If user-controlled data must be added to an expression interpreter, one or more of the following should be performed:
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".
Detection Methods
- Automated Static Analysis High — Automated static analysis, commonly referred to as Static Application Security Testing (SAST), can find some instances of this weakness by analyzing source code (or binary/compiled code) without having to execute it. Typically, this is done by building a model of data flow and control flow, then sea
Real-World CVE Examples
| CVE ID | Description |
|---|---|
| CVE-2021-44228 | Product does not neutralize ${xyz} style expressions, allowing remote code execution. (log4shell vulnerability in log4j) |
Related Weaknesses
Frequently Asked Questions
What is CWE-917?
CWE-917 (Improper Neutralization of Special Elements used in an Expression Language Statement ('Expression Language Injection')) is a software weakness identified by MITRE's Common Weakness Enumeration. It is classified as a Base-level weakness. 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 no...
How can CWE-917 be exploited?
Attackers can exploit CWE-917 (Improper Neutralization of Special Elements used in an Expression Language Statement ('Expression Language Injection')) to read application data. This weakness is typically introduced during the Architecture and Design, Implementation phase of software development.
How do I prevent CWE-917?
Key mitigations include: Avoid adding user-controlled data into an expression interpreter when possible.
What is the severity of CWE-917?
CWE-917 is classified as a Base-level weakness (Medium abstraction). It has been observed in 1 real-world CVEs.