CWE-184 Base Draft

Incomplete List of Disallowed Inputs

This vulnerability occurs when a security filter or validation mechanism relies on a 'denylist'—a predefined list of forbidden inputs—but that list is missing critical entries. Attackers can bypass…

Definition

What is CWE-184?

This vulnerability occurs when a security filter or validation mechanism relies on a 'denylist'—a predefined list of forbidden inputs—but that list is missing critical entries. Attackers can bypass the protection by using variations or inputs the developers didn't anticipate.
Denylist-based security is fundamentally fragile because it requires developers to predict and block every possible bad input. This approach often fails against sophisticated attacks, as attackers constantly evolve their techniques to use new encodings, character sequences, or command variations that aren't on the list. Relying solely on a denylist creates a false sense of security and is difficult to maintain over time. For stronger protection, prioritize 'allowlisting' (only permitting known-good patterns) over denylisting. If a denylist is unavoidable, complement it with other defenses like strict input validation, output encoding, and security libraries designed to handle the specific threat. Always assume your denylist is incomplete and design your system to fail safely when an unexpected input is encountered.
Vulnerability Diagram CWE-184
Incomplete Blocklist Block list <script> ✗ <SCRIPT> ? <ScRiPt> ? <img onerror> ? javascript: ? Bypass payloads <ScRiPt>…</ScRiPt> <img src=x onerror=…> SELECT/**/* FROM ..%2f..%2fetc Reaches sink XSS / SQLi / traversal still works Denylists miss case, encoding and equivalent forms — use allowlists.
Auswirkungen in der Praxis

Real-world CVEs caused by CWE-184

  • CVE-2024-4315

    Chain: API for text generation using Large Language Models (LLMs) does not include the "\" Windows folder separator in its denylist (CWE-184) when attempting to prevent Local File Inclusion via path traversal (CWE-22), allowing deletion of arbitrary files on Windows systems.

  • CVE-2008-2309

    product uses a denylist to identify potentially dangerous content, allowing attacker to bypass a warning

  • CVE-2005-2782

    PHP remote file inclusion in web application that filters "http" and "https" URLs, but not "ftp".

  • CVE-2004-0542

    Programming language does not filter certain shell metacharacters in Windows environment.

  • CVE-2004-0595

    XSS filter doesn't filter null characters before looking for dangerous tags, which are ignored by web browsers. MIE and validate-before-cleanse.

  • CVE-2005-3287

    Web-based mail product doesn't restrict dangerous extensions such as ASPX on a web server, even though others are prohibited.

  • CVE-2004-2351

    Resultant XSS when only and are checked.

  • CVE-2005-2959

    Privileged program does not clear sensitive environment variables that are used by bash. Overlaps multiple interpretation error.

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 Java

The following code attempts to stop XSS attacks by removing all occurences of "script" in an input string.

Verwundbar Java 
public String removeScriptTags(String input, String mask) {
  	return input.replaceAll("script", mask);
  }
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-184

  • Implementation Do not rely exclusively on detecting disallowed inputs. There are too many variants to encode a character, especially when different environments are used, so there is a high likelihood of missing some variants. Only use detection of disallowed inputs as a mechanism for detecting suspicious activity. Ensure that you are using other protection mechanisms that only identify "good" input - such as lists of allowed inputs - and ensure that you are properly encoding your outputs.
Erkennungssignale

How to detect CWE-184

Black Box

Exploitation of a vulnerability with commonly-used manipulations might fail, but minor variations might succeed.

Plexicus Auto-Fix

Plexicus erkennt CWE-184 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.

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Häufig gestellte Fragen

Frequently asked questions

Was ist CWE-184?

This vulnerability occurs when a security filter or validation mechanism relies on a 'denylist'—a predefined list of forbidden inputs—but that list is missing critical entries. Attackers can bypass the protection by using variations or inputs the developers didn't anticipate.

Wie gravierend ist CWE-184?

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-184 betroffen?

MITRE hat für diese CWE keine betroffenen Plattformen spezifiziert — sie kann in den meisten Anwendungs-Stacks auftreten.

Wie kann ich CWE-184 verhindern?

Do not rely exclusively on detecting disallowed inputs. There are too many variants to encode a character, especially when different environments are used, so there is a high likelihood of missing some variants. Only use detection of disallowed inputs as a mechanism for detecting suspicious activity. Ensure that you are using other protection mechanisms that only identify "good" input - such as lists of allowed inputs - and ensure that you are properly encoding your outputs.

Wie erkennt und behebt Plexicus CWE-184?

Die SAST-Engine von Plexicus erkennt die Datenfluss-Signatur von CWE-184 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-184?

MITRE veröffentlicht die kanonische Definition unter https://cwe.mitre.org/data/definitions/184.html. Für ergänzende Hinweise kannst du auch die OWASP- und NIST-Dokumentation heranziehen.

Verwandte Schwachstellen

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CWE-1269 Sibling

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CWE-1278 Sibling

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CWE-1291 Sibling

Public Key Re-Use for Signing both Debug and Production Code

This vulnerability occurs when the same cryptographic key is used to sign both development/debug software builds and final production…

CWE-1318 Sibling

Missing Support for Security Features in On-chip Fabrics or Buses

This vulnerability occurs when the communication channels (fabrics or buses) within a chip lack built-in or enabled security features,…

CWE-1319 Sibling

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This vulnerability occurs when a hardware device lacks sufficient shielding against electromagnetic interference, allowing attackers to…

Ressourcen

Further reading

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