CWE-917: Improper Neutralization of Special Elements used in an Expression Language Statement ('Expression Language Injection')

BaseIncomplete

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.

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Extended Description

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.

Technical Details

Structure
Simple
Vulnerability Mapping
ALLOWED

Applicable To

Languages
Java
Platforms

Source-backed guidance

Additional facts reviewed against primary or authoritative security sources.

Verify controls for CWE-917 with SSDF evidence

Use NIST SSDF verification and vulnerability-response practices to detect CWE-917, Improper Neutralization of Special Elements used in an Expression Language Statement ('Expression Language Injection'), throughout the product lifecycle. Derive review questions, static or dynamic checks, and negative tests from the CWE's causal behavior; define the components and lifecycle stages each check covers; and retain findings with enough evidence to distinguish the root cause from symptoms and impacts. Track escapes and false negatives, then improve the verification plan after every confirmed occurrence.

NIST SP 800-218 Secure Software Development Framework — National Institute of Standards and Technology

Address Improper Neutralization of Special Elements used in an Expression Language Statement during Architecture and Design

MITRE associates mitigation with Architecture and Design, Implementation, System Configuration, and Operation; documented detection approaches include Automated Static Analysis; recorded impacts include Read Application Data, and Execute Unauthorized Code or Commands. Use these source-defined anchors to turn CWE-917 into implementation, review, and verification checks for the affected component.

CWE-917: Improper Neutralization of Special Elements used in an Expression Language Statement ('Expression Language Injection') — MITRE CWE

Triage CWE-917 against known exploitation evidence

Use CISA's Known Exploited Vulnerabilities catalog to test whether a vulnerability mapped to CWE-917, Improper Neutralization of Special Elements used in an Expression Language Statement ('Expression Language Injection'), has evidence of exploitation in the wild. Confirm the CVE-to-CWE root-cause mapping independently before attaching the example, then capture the affected product, required action, and remediation deadline. A missing KEV match is not evidence that the weakness is unexploited, and a KEV entry must not be generalized to every occurrence of this CWE.

Known Exploited Vulnerabilities Catalog — Cybersecurity and Infrastructure Security Agency

Apply precise root-cause mapping to CWE-917

Apply MITRE's full root-cause mapping guidance when using CWE-917, Improper Neutralization of Special Elements used in an Expression Language Statement ('Expression Language Injection'). Separate weakness language from attacker prerequisites and technical impact, check the entry's abstraction and vulnerability-mapping notes, and prefer the most specific Base or Variant supported by the evidence. Record the rejected alternatives and require an independent review before the mapping is used for remediation trends or program metrics.

CVE to CWE Root Cause Mapping Guidance — MITRE CWE

Validate CWE-917 with root-cause mapping checks

Apply MITRE's root-cause mapping quick tips to CWE-917, Improper Neutralization of Special Elements used in an Expression Language Statement ('Expression Language Injection'). Confirm the finding describes the causal weakness rather than an impact or attack pattern, compare the abstraction and mapping notes with plausible alternatives, and have a second reviewer challenge the selection. Preserve the evidence and reasoning so recurring defects can be measured against one consistent identifier.

CVE to CWE Root Cause Mapping Quick Tips — MITRE CWE

Frequently Asked Questions

What is CWE-917: Improper Neutralization of Special Elements used in an Expression Language Statement ('Expression Language Injection')?+

CWE-917: Improper Neutralization of Special Elements used in an Expression Language Statement ('Expression Language Injection') is a Common Weakness Enumeration (CWE) entry maintained by MITRE. 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.

What are the security consequences of Improper Neutralization of Special Elements used in an Expression Language Statement ('Expression Language Injection')?+

If exploited, CWE-917 (Improper Neutralization of Special Elements used in an Expression Language Statement ('Expression Language Injection')) it can compromise Confidentiality and Integrity, leading to outcomes such as Read Application Data and Execute Unauthorized Code or Commands.

How do you prevent or mitigate Improper Neutralization of Special Elements used in an Expression Language Statement ('Expression Language Injection')?+

Recommended mitigations for CWE-917 include: 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: 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 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".

Which programming languages are affected by Improper Neutralization of Special Elements used in an Expression Language Statement ('Expression Language Injection')?+

CWE-917 commonly affects Java. Note that weaknesses are often language-agnostic patterns, so secure coding practices apply broadly.

What are real-world examples of Improper Neutralization of Special Elements used in an Expression Language Statement ('Expression Language Injection')?+

MITRE documents real CVEs mapped to CWE-917, including CVE-2021-44228. You can look up the full details of each CVE, including CVSS scores and remediation guidance, on our CVE Lookup tool.

What is the difference between a CWE and a CVE?+

A CWE (Common Weakness Enumeration) like CWE-917 describes a category of software weakness — the underlying flaw type. A CVE (Common Vulnerabilities and Exposures) identifies a specific, real-world vulnerability in a particular product. In short, a CWE is the kind of mistake, and a CVE is an instance of that mistake being found in software.

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