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.)
CWE-191 Base Brouillon
Integer Underflow (Wrap or Wraparound)
Integer underflow occurs when a subtraction operation results in a value smaller than the data type's minimum limit, causing the value to wrap around to a large, incorrect number.
Définition
What is CWE-191?
Integer underflow occurs when a subtraction operation results in a value smaller than the data type's minimum limit, causing the value to wrap around to a large, incorrect number.
Integer underflow, also known as wraparound, happens when a program subtracts a larger number from a smaller one, pushing the result below the minimum value the integer type can hold. Instead of throwing an error, the value wraps around to the maximum end of the range—for example, an unsigned 8-bit integer going from 0 to 255 after subtracting 1. This creates a logic flaw where the program operates on a wildly incorrect value, often leading to unexpected behavior.
This vulnerability affects both signed and unsigned integers and is a common source of critical security flaws. In signed integers, underflow can flip a positive value to a massive negative one, while in unsigned integers, it creates an unexpectedly large positive value. Developers must validate all subtraction inputs, use safe math libraries, or choose data types with sufficient range to prevent these dangerous wrap-around scenarios.
Impact réel
Real-world CVEs caused by CWE-191
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Integer underflow in firewall via malformed packet.
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Integer underflow by packet with invalid length.
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Long input causes incorrect length calculation.
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Malformed icon causes integer underflow in loop counter variable.
Comment les attaquants l'exploitent
Parcours de l'attaquant étape par étape
- 1
The following example subtracts from a 32 bit signed integer.
- 2
The example has an integer underflow. The value of i is already at the lowest negative value possible, so after subtracting 1, the new value of i is 2147483647.
- 3
This code performs a stack allocation based on a length calculation.
- 4
Since a and b are declared as signed ints, the "a - b" subtraction gives a negative result (-1). However, since len is declared to be unsigned, len is cast to an extremely large positive number (on 32-bit systems - 4294967295). As a result, the buffer buf[len] declaration uses an extremely large size to allocate on the stack, very likely more than the entire computer's memory space.
- 5
Miscalculations usually will not be so obvious. The calculation will either be complicated or the result of an attacker's input to attain the negative value.
Exemple de code vulnérable
Vulnerable C
The following example subtracts from a 32 bit signed integer.
#include <stdio.h>
#include <stdbool.h>
main (void)
{
int i;
i = -2147483648;
i = i - 1;
return 0;
} Exemple de code sécurisé
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.
Liste de contrôle de prévention
How to prevent CWE-191
- Architecture Use safe-by-default frameworks and APIs that prevent the unsafe pattern from being expressible.
- Implementation Validate input at trust boundaries; use allowlists, not denylists.
- Implementation Apply the principle of least privilege to credentials, file paths, and runtime permissions.
- Testing Cover this weakness in CI: SAST rules + targeted unit tests for the data flow.
- Operation Monitor logs for the runtime signals listed in the next section.
Signaux de détection
How to detect CWE-191
Plexicus détecte automatiquement CWE-191 et ouvre une PR de correction en moins de 60 secondes.
Codex Remedium analyse chaque commit, identifie cette faiblesse précise et livre une pull request prête à être relue avec le correctif. Pas de tickets. Pas de transferts.
Questions fréquentes Qu'est-ce que CWE-191 ?
Quelle est la gravité de CWE-191 ?
Quels langages ou plateformes sont affectés par CWE-191 ?
Comment puis-je prévenir CWE-191 ?
Comment Plexicus détecte et corrige CWE-191 ?
Où puis-je en savoir plus sur CWE-191 ?
Frequently asked questions
Qu'est-ce que CWE-191 ?
Integer underflow occurs when a subtraction operation results in a value smaller than the data type's minimum limit, causing the value to wrap around to a large, incorrect number.
Quelle est la gravité de CWE-191 ?
MITRE n'a pas publié de note de probabilité d'exploitation pour cette faiblesse. Traitez-la comme un impact moyen jusqu'à ce que votre modèle de menace prouve le contraire.
Quels langages ou plateformes sont affectés par CWE-191 ?
MITRE lists the following affected platforms: C, C++, Java, C#.
Comment puis-je prévenir CWE-191 ?
Use safe-by-default frameworks, validate untrusted input at trust boundaries, and apply the principle of least privilege. Cover the data-flow signature in CI with SAST.
Comment Plexicus détecte et corrige CWE-191 ?
Le moteur SAST de Plexicus reconnaît la signature de flux de données de CWE-191 à chaque commit. Lorsqu'une correspondance est trouvée, notre agent Codex Remedium ouvre une PR de correction avec le code corrigé, les tests et un résumé d'une ligne pour le relecteur.
Où puis-je en savoir plus sur CWE-191 ?
MITRE publie la définition canonique à https://cwe.mitre.org/data/definitions/191.html. Vous pouvez également consulter la documentation OWASP et NIST pour des conseils adjacents.
Faiblesses associées
Weaknesses related to CWE-191
CWE-682 Parent
Incorrect Calculation
This vulnerability occurs when software performs a calculation that produces wrong or unexpected results, which are then used to make…
CWE-128 Frère
Wrap-around Error
A wrap-around error happens when a variable exceeds the maximum value its data type can hold, causing it to unexpectedly reset to a very…
CWE-131 Frère
Incorrect Calculation of Buffer Size
This vulnerability occurs when a program miscalculates the amount of memory needed for a buffer, potentially leading to a buffer overflow…
CWE-1335 Frère
Incorrect Bitwise Shift of Integer
This vulnerability occurs when a program attempts to shift an integer's bits by an invalid amount—either a negative number or a value…
CWE-1339 Frère
Insufficient Precision or Accuracy of a Real Number
This vulnerability occurs when a program uses a data type or algorithm that cannot accurately represent or calculate the fractional part…
CWE-135 Frère
Incorrect Calculation of Multi-Byte String Length
This vulnerability occurs when software incorrectly measures the length of strings containing multi-byte or wide characters, leading to…
CWE-190 Frère
Integer Overflow or Wraparound
Integer overflow or wraparound occurs when a calculation produces a numeric result that exceeds the maximum value a variable can hold.…
CWE-193 Frère
Off-by-one Error
An off-by-one error occurs when a program incorrectly calculates a boundary, such as a loop counter or array index, by being one unit too…
CWE-369 Frère
Divide By Zero
A divide-by-zero error occurs when software attempts to perform a division operation where the denominator is zero.
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