CWE-917 Base Incomplete

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

Expression Language Injection occurs when an application uses untrusted, external input to build an expression language statement—common in frameworks like Java Server Pages (JSP)—without properly…

Definition

What is CWE-917?

Expression Language Injection occurs when an application uses untrusted, external input to build an expression language statement—common in frameworks like Java Server Pages (JSP)—without properly sanitizing it. This allows an attacker to inject malicious expressions that alter the intended logic and execute arbitrary code when the statement is processed.
Frameworks like JSP allow developers to embed dynamic expressions directly into web pages. If these expression evaluation features are left enabled and user input flows into them without validation, attackers can craft inputs that break out of the intended data context. The injected expressions are then executed on the server, potentially leading to data exposure, system compromise, or other unexpected behavior. Preventing this requires disabling expression evaluation where it's not needed, rigorously validating and sanitizing all user inputs that touch expression contexts, and adopting a secure coding policy for the framework. Managing this at scale across a large codebase is difficult; an ASPM like Plexicus can help you track and remediate these flaws across your entire stack. While SAST tools catch the vulnerable pattern, Plexicus uses AI to suggest the actual code fix, saving hours of manual security work.
Auswirkungen in der Praxis

Real-world CVEs caused by CWE-917

  • CVE-2021-44228

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

Wie Angreifer es ausnutzen

Angreiferpfad Schritt für Schritt

  1. 1

    Identifiziere einen Codepfad, der nicht vertrauenswürdige Eingaben ohne Validierung verarbeitet.

  2. 2

    Erzeuge eine Payload, die das unsichere Verhalten auslöst — Injection, Traversal, Overflow oder Logik-Missbrauch.

  3. 3

    Liefere die Payload über einen normalen Request aus und beobachte die Reaktion der Anwendung.

  4. 4

    Iteriere, bis die Antwort Daten preisgibt, Angreifer-Code ausführt oder Berechtigungen eskaliert.

Verwundbares Codebeispiel

Vulnerable pseudo

MITRE hat kein Codebeispiel für diese CWE veröffentlicht. Das untenstehende Muster ist illustrativ — kanonische Referenzen findest du unter Ressourcen.

Verwundbar pseudo 
// Example pattern — see MITRE for the canonical references.
function handleRequest(input) {
  // Untrusted input flows directly into the sensitive sink.
  return executeUnsafe(input);
}
Sicheres Codebeispiel

Secure pseudo

Sicher pseudo 
// Validate, sanitize, or use a safe API before reaching the sink.
function handleRequest(input) {
  const safe = validateAndEscape(input);
  return executeWithGuards(safe);
}
What changed: the unsafe sink is replaced (or the input is validated/escaped) so the same payload no longer triggers the weakness.
Präventions-Checkliste

How to prevent CWE-917

  • 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".
Erkennungssignale

How to detect CWE-917

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 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.)

Plexicus Auto-Fix

Plexicus erkennt CWE-917 automatisch und öffnet in unter 60 Sekunden einen Fix-PR.

Codex Remedium scannt jeden Commit, identifiziert genau diese Schwachstelle und liefert einen reviewer-ready Pull Request mit dem Patch. Keine Tickets. Keine Hand-offs.

Demo anfordern Plexicus kostenlos testen
Häufig gestellte Fragen

Frequently asked questions

Was ist CWE-917?

Expression Language Injection occurs when an application uses untrusted, external input to build an expression language statement—common in frameworks like Java Server Pages (JSP)—without properly sanitizing it. This allows an attacker to inject malicious expressions that alter the intended logic and execute arbitrary code when the statement is processed.

Wie gravierend ist CWE-917?

MITRE hat für diese Schwachstelle keine Exploit-Wahrscheinlichkeit veröffentlicht. Behandle sie als mittlere Auswirkung, bis dein Threat Model anderes belegt.

Welche Sprachen oder Plattformen sind von CWE-917 betroffen?

MITRE lists the following affected platforms: Java.

Wie kann ich CWE-917 verhindern?

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

Wie erkennt und behebt Plexicus CWE-917?

Die SAST-Engine von Plexicus erkennt die Datenfluss-Signatur von CWE-917 bei jedem Commit. Bei einem Treffer öffnet unser Codex-Remedium-Agent einen Fix-PR mit korrigiertem Code, Tests und einer einzeiligen Zusammenfassung für den Reviewer.

Wo erfahre ich mehr über CWE-917?

MITRE veröffentlicht die kanonische Definition unter https://cwe.mitre.org/data/definitions/917.html. Für ergänzende Hinweise kannst du auch die OWASP- und NIST-Dokumentation heranziehen.

Verwandte Schwachstellen

Weaknesses related to CWE-917

CWE-77 Parent

Improper Neutralization of Special Elements used in a Command ('Command Injection')

This vulnerability occurs when an application builds a system command using untrusted user input without properly sanitizing it. An…

CWE-1427 Sibling

Improper Neutralization of Input Used for LLM Prompting

This vulnerability occurs when an application builds prompts for a Large Language Model (LLM) using external data, but does so in a way…

CWE-624 Sibling

Executable Regular Expression Error

This vulnerability occurs when an application uses a regular expression that can execute code, either because it directly contains…

CWE-78 Sibling

Improper Neutralization of Special Elements used in an OS Command ('OS Command Injection')

OS Command Injection occurs when an application builds a system command using untrusted, external input without properly sanitizing it.…

CWE-88 Sibling

Improper Neutralization of Argument Delimiters in a Command ('Argument Injection')

This vulnerability occurs when an application builds a command string for execution by another component, but fails to properly separate…

CWE-1336 Peer

Improper Neutralization of Special Elements Used in a Template Engine

This vulnerability occurs when an application uses a template engine to process user-controlled input but fails to properly sanitize…

Ressourcen

Further reading

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