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CWE-166 Base Draft
Improper Handling of Missing Special Element
This vulnerability occurs when software expects a specific delimiter, terminator, or other special marker in its input but fails to properly handle situations where that element is absent. The…
Definition
What is CWE-166?
This vulnerability occurs when software expects a specific delimiter, terminator, or other special marker in its input but fails to properly handle situations where that element is absent. The application may then misinterpret boundaries, leading to crashes, data corruption, or security breaches.
Think of this like a sentence missing its period. Without the expected terminator, the software doesn't know where the input ends. It might continue reading into adjacent memory or system buffers, treating regular data as commands. This often happens when parsing structured data like strings, headers, or protocol messages where a special character defines the end of a field.
To prevent this, developers must write robust input validation that explicitly checks for the presence and correct placement of required special elements. Implement strict parsing logic with clear boundaries and use safe functions that limit read operations. Always define and handle error cases for malformed input, ensuring the system fails securely instead of proceeding with corrupted or dangerous assumptions.
Auswirkungen in der Praxis
Real-world CVEs caused by CWE-166
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Crash via message type without separator character
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Missing special character (separator) causes crash
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HTTP GET without \r\n\r\n CRLF sequences causes product to wait indefinitely and prevents other users from accessing it
Wie Angreifer es ausnutzen
Angreiferpfad Schritt für Schritt
- 1
Identifiziere einen Codepfad, der nicht vertrauenswürdige Eingaben ohne Validierung verarbeitet.
- 2
Erzeuge eine Payload, die das unsichere Verhalten auslöst — Injection, Traversal, Overflow oder Logik-Missbrauch.
- 3
Liefere die Payload über einen normalen Request aus und beobachte die Reaktion der Anwendung.
- 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.
// 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
// 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-166
- Developers should anticipate that special elements will be removed in the input vectors of their product. Use an appropriate combination of denylists and allowlists to ensure only valid, expected and appropriate input is processed by the system.
- Implementation Assume all input is malicious. Use an "accept known good" input validation strategy, i.e., use a list of acceptable inputs that strictly conform to specifications. Reject any input that does not strictly conform to specifications, or transform it into something that does. When performing input validation, consider all potentially relevant properties, including length, type of input, the full range of acceptable values, missing or extra inputs, syntax, consistency across related fields, and conformance to business rules. As an example of business rule logic, "boat" may be syntactically valid because it only contains alphanumeric characters, but it is not valid if the input is only expected to contain colors such as "red" or "blue." Do not rely exclusively on looking for malicious or malformed inputs. This is likely to miss at least one undesirable input, especially if the code's environment changes. This can give attackers enough room to bypass the intended validation. However, denylists can be useful for detecting potential attacks or determining which inputs are so malformed that they should be rejected outright.
- Implementation Inputs should be decoded and canonicalized to the application's current internal representation before being validated (CWE-180). Make sure that the application does not decode the same input twice (CWE-174). Such errors could be used to bypass allowlist validation schemes by introducing dangerous inputs after they have been checked.
Erkennungssignale
How to detect CWE-166
Führe dynamische Application-Security-Tests gegen den Live-Endpoint aus.
Beobachte Runtime-Logs auf ungewöhnliche Exception-Traces, fehlerhafte Eingaben oder Versuche, Autorisierung zu umgehen.
Code Review: Markiere jeden neuen Code, der Eingaben von dieser Oberfläche ohne validierte Framework-Helper verarbeitet.
CWE-166
Don't catalog this weakness. Prove it's reachable.
Plexicus turns CWE catalogs into evidence: every CWE-pattern is matched against your real code graph, reach is proven on a sandbox clone, and verified findings ship as reviewed PRs.
Häufig gestellte Fragen Was ist CWE-166?
Wie gravierend ist CWE-166?
Welche Sprachen oder Plattformen sind von CWE-166 betroffen?
Wie kann ich CWE-166 verhindern?
Wie erkennt und behebt Plexicus CWE-166?
Wo erfahre ich mehr über CWE-166?
Frequently asked questions
Was ist CWE-166?
This vulnerability occurs when software expects a specific delimiter, terminator, or other special marker in its input but fails to properly handle situations where that element is absent. The application may then misinterpret boundaries, leading to crashes, data corruption, or security breaches.
Wie gravierend ist CWE-166?
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-166 betroffen?
MITRE hat für diese CWE keine betroffenen Plattformen spezifiziert — sie kann in den meisten Anwendungs-Stacks auftreten.
Wie kann ich CWE-166 verhindern?
Developers should anticipate that special elements will be removed in the input vectors of their product. Use an appropriate combination of denylists and allowlists to ensure only valid, expected and appropriate input is processed by the system. Assume all input is malicious. Use an "accept known good" input validation strategy, i.e., use a list of acceptable inputs that strictly conform to specifications. Reject any input that does not strictly conform to specifications, or transform it into…
Wie erkennt und behebt Plexicus CWE-166?
Die SAST-Engine von Plexicus erkennt die Datenfluss-Signatur von CWE-166 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-166?
MITRE veröffentlicht die kanonische Definition unter https://cwe.mitre.org/data/definitions/166.html. Für ergänzende Hinweise kannst du auch die OWASP- und NIST-Dokumentation heranziehen.
Verwandte Schwachstellen
Weaknesses related to CWE-166
CWE-159 Parent
Improper Handling of Invalid Use of Special Elements
This vulnerability occurs when an application fails to properly validate or neutralize special characters and control elements within…
CWE-167 Sibling
Improper Handling of Additional Special Element
This vulnerability occurs when software receives data from another component but fails to properly process or validate unexpected special…
CWE-168 Sibling
Improper Handling of Inconsistent Special Elements
This vulnerability occurs when software fails to correctly process input containing conflicting or mismatched special elements like…
Ressourcen
Further reading
Bereit, das Wesentliche zu validieren?
Bereit zu validieren, was zählt.
Plexicus ist Proof-Driven AppSec: validierte Funde, kontextuelles Verständnis und geprüfte Remediation — in Evidenz verankert, mit Ihnen gescoped.