CWE-917 Detail

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.

Modes Of Introduction

Architecture and Design
Implementation

Applicable Platforms

Language

Name: Java (Undetermined)

Common Consequences

Observed Examples

Potential Mitigations

Phases : Architecture and Design
Avoid adding user-controlled data into an expression interpreter when possible.
Phases : 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

Phases : 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".

Detection Methods

Automated Static Analysis

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 searching for potentially-vulnerable patterns that connect "sources" (origins of input) with "sinks" (destinations where the data interacts with external components, a lower layer such as the OS, etc.)
Effectiveness : High

Vulnerability Mapping Notes

Justification : This CWE entry is at the Base level of abstraction, which is a preferred level of abstraction for mapping to the root causes of vulnerabilities.
Comment : Carefully read both the name and description to ensure that this mapping is an appropriate fit. Do not try to 'force' a mapping to a lower-level Base/Variant simply to comply with this preferred level of abstraction.

NotesNotes

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.

References

REF-911

Expression Language Injection
Stefano Di Paola, Arshan Dabirsiaghi.
https://mindedsecurity.com/wp-content/uploads/2020/10/ExpressionLanguageInjection.pdf

REF-912

Remote Code with Expression Language Injection
Dan Amodio.
http://danamodio.com/appsec/research/spring-remote-code-with-expression-language-injection/

REF-1279

Neutralizing Your Inputs: A Log4Shell Weakness Story
CWE/CAPEC.
https://medium.com/@CWE_CAPEC/neutralizing-your-inputs-a-log4shell-weakness-story-89954c8b25c9

REF-1280

Expression Language Injection
OWASP.
https://owasp.org/www-community/vulnerabilities/Expression_Language_Injection

Submission

Modifications