Führe statische Analyse (SAST) auf der Codebasis aus und suche im Datenfluss nach dem unsicheren Muster.
CWE-196 Variant Draft
Unsigned to Signed Conversion Error
This vulnerability occurs when a program takes an unsigned integer and converts it directly to a signed integer. If the original unsigned value is too large to fit within the signed type's positive…
Definition
What is CWE-196?
This vulnerability occurs when a program takes an unsigned integer and converts it directly to a signed integer. If the original unsigned value is too large to fit within the signed type's positive range, the conversion results in an unexpected negative number, corrupting the data.
While less common than signed-to-unsigned errors, this conversion flaw is a critical enabler for buffer underwrite attacks. When a large unsigned value (like a size or index) becomes a large negative number after conversion, using it for array indexing or pointer arithmetic can shift memory access far below the intended buffer's start. This "underwrite" or "buffer underflow" grants attackers write access to sensitive stack memory, such as function return addresses or saved registers, which they typically cannot reach in a standard overflow.
This vulnerability is particularly dangerous because it subverts common security assumptions. Developers often guard against overly large positive values but may not anticipate an index turning negative. The resulting out-of-bounds write can lead to arbitrary code execution, often with fewer detection hurdles than a classic buffer overflow, making it a subtle but powerful exploit precursor.
Auswirkungen in der Praxis
Real-world CVEs caused by CWE-196
Bisher sind in MITREs Katalog keine öffentlichen CVE-Referenzen mit dieser CWE verknüpft.
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-196
- Requirements Choose a language which is not subject to these casting flaws.
- Architecture and Design Design object accessor functions to implicitly check values for valid sizes. Ensure that all functions which will be used as a size are checked previous to use as a size. If the language permits, throw exceptions rather than using in-band errors.
- Implementation Error check the return values of all functions. Be aware of implicit casts made, and use unsigned variables for sizes if at all possible.
Erkennungssignale
How to detect CWE-196
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-196
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-196?
Wie gravierend ist CWE-196?
Welche Sprachen oder Plattformen sind von CWE-196 betroffen?
Wie kann ich CWE-196 verhindern?
Wie erkennt und behebt Plexicus CWE-196?
Wo erfahre ich mehr über CWE-196?
Frequently asked questions
Was ist CWE-196?
This vulnerability occurs when a program takes an unsigned integer and converts it directly to a signed integer. If the original unsigned value is too large to fit within the signed type's positive range, the conversion results in an unexpected negative number, corrupting the data.
Wie gravierend ist CWE-196?
MITRE stuft die Exploit-Wahrscheinlichkeit als mittel ein — eine Ausnutzung ist realistisch, erfordert aber meist bestimmte Bedingungen.
Welche Sprachen oder Plattformen sind von CWE-196 betroffen?
MITRE lists the following affected platforms: C, C++.
Wie kann ich CWE-196 verhindern?
Choose a language which is not subject to these casting flaws. Design object accessor functions to implicitly check values for valid sizes. Ensure that all functions which will be used as a size are checked previous to use as a size. If the language permits, throw exceptions rather than using in-band errors.
Wie erkennt und behebt Plexicus CWE-196?
Die SAST-Engine von Plexicus erkennt die Datenfluss-Signatur von CWE-196 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-196?
MITRE veröffentlicht die kanonische Definition unter https://cwe.mitre.org/data/definitions/196.html. Für ergänzende Hinweise kannst du auch die OWASP- und NIST-Dokumentation heranziehen.
Verwandte Schwachstellen
Weaknesses related to CWE-196
CWE-681 Parent
Incorrect Conversion between Numeric Types
This vulnerability occurs when a program converts a value from one numeric type to another (like a 64-bit integer to a 32-bit integer) and…
CWE-192 Sibling
Integer Coercion Error
An integer coercion error occurs when a program incorrectly converts, extends, or truncates a number between different data types, leading…
CWE-194 Sibling
Unexpected Sign Extension
This vulnerability occurs when a signed number from a smaller data type is moved or cast to a larger type, causing its sign bit to be…
CWE-195 Sibling
Signed to Unsigned Conversion Error
This vulnerability occurs when a signed integer (which can hold negative values) is converted to an unsigned integer (which holds only…
CWE-197 Sibling
Numeric Truncation Error
A numeric truncation error happens when a program converts a number to a smaller data type, cutting off its higher-order bits and…
CWE-124 Peer
Buffer Underwrite ('Buffer Underflow')
A buffer underwrite, also known as buffer underflow, happens when a program writes data to a memory location before the official start of…
CWE-120 Peer
Buffer Copy without Checking Size of Input ('Classic Buffer Overflow')
This vulnerability occurs when a program copies data from one memory location to another without first verifying that the source data will…
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.