cwe-917-expression-language-injection

name: cwe-917-expression-language-injection description: Use this skill when you need to remediate CWE-917 (Expression Language Injection) vulnerabilities in Java code. Triggers on SAST findings, security reviews, or when fixing expression language injection issues. version: 1.0.0 license: MIT tags:

• security

• java

• cwe-917

• remediation

• sast

• expression-injection

• spel

• injection

CWE-917 Expression Language Injection

Description

Expression Language Injection

Reference: https://cwe.mitre.org/data/definitions/917.html

OWASP Category: A03:2021 – Injection

Vulnerable Pattern

❌ Example 1: Vulnerable Pattern

// VULNERABLE: Using StandardEvaluationContext allows access to dangerous types
StandardEvaluationContext context = new StandardEvaluationContext();
context.setVariable("input", userInput);
Expression expression = parser.parseExpression(userExpression);
Object result = expression.getValue(context);

Why it's vulnerable: This pattern is vulnerable to Expression Language Injection

Deterministic Fix

✅ Secure Implementation: Secure Implementation

// SECURE: SimpleEvaluationContext restricts type access
SimpleEvaluationContext context = SimpleEvaluationContext
    .forReadOnlyDataBinding()
    .withInstanceMethods()
    .build();
// Only allow safe expressions, reject user-controlled expression strings
Expression expression = parser.parseExpression(PREDEFINED_EXPRESSION);
Object result = expression.getValue(context, targetObject);

Why it's secure: Implements proper protection against Expression Language Injection

Detection Pattern

Look for these patterns in your codebase:

# Find StandardEvaluationContext usage
grep -rn "StandardEvaluationContext" --include="*.java"

# Find SpEL parsing with user input
grep -rn "parseExpression" --include="*.java" | grep -E "getParameter|request"

Remediation Steps

1. Replace StandardEvaluationContext with SimpleEvaluationContext

2. Use forReadOnlyDataBinding() to restrict property access

3. Never parse user-controlled expression strings

4. Whitelist allowed expression patterns if dynamic expressions are required

Key Imports

import org.springframework.expression.spel.support.SimpleEvaluationContext;

import org.springframework.expression.spel.standard.SpelExpressionParser;

Verification

After remediation:

• Run SAST scanner to confirm vulnerability is resolved

• Review all instances of the vulnerable pattern

• Add unit tests that verify the secure implementation

• Check for similar patterns in related code

Trigger Examples

Fix CWE-917 vulnerability
Resolve Expression Language Injection issue
Secure this Java code against expression language injection
SAST reports CWE-917

Common Vulnerable Locations

| Controller | *Controller.java | User input handling |

| Service | *Service.java | Business logic |

| Repository | *Repository.java | Data access |

References

• CWE-917: Expression Language Injection

• Spring SpEL Documentation

Source: Generated by Java CWE Security Skills Generator Last Updated: 2026-03-07