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-338 Base Borrador
Use of Cryptographically Weak Pseudo-Random Number Generator (PRNG)
This vulnerability occurs when software uses a pseudo-random number generator (PRNG) that is not cryptographically strong for security-sensitive operations, such as generating keys, tokens, or…
Definición
What is CWE-338?
This vulnerability occurs when software uses a pseudo-random number generator (PRNG) that is not cryptographically strong for security-sensitive operations, such as generating keys, tokens, or initialization vectors.
Using a non-cryptographic PRNG in a security context can expose your application to attacks. Attackers can often predict or reproduce the generated numbers, allowing them to forge sessions, decrypt data, or bypass authentication. This happens because these generators prioritize speed and efficiency over the unpredictability required for secure cryptography.
Developers sometimes choose weaker PRNGs for performance reasons or because they are readily available in standard libraries. However, features that make these PRNGs efficient—like small internal states or deterministic seeding—are the same features that make them easy to break. For any security-related function, you must use a cryptographically secure pseudo-random number generator (CSPRNG) designed to withstand such analysis.
Impacto en el mundo real
Real-world CVEs caused by CWE-338
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PHP framework uses mt_rand() function (Marsenne Twister) when generating tokens
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Crypto product uses rand() library function to generate a recovery key, making it easier to conduct brute force attacks.
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Random number generator can repeatedly generate the same value.
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Web application generates predictable session IDs, allowing session hijacking.
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SSL library uses a weak random number generator that only generates 65,536 unique keys.
Cómo lo explotan los atacantes
Ruta del atacante paso a paso
- 1
Identifica una ruta de código que maneje entrada no confiable sin validación.
- 2
Crea un payload que ejercite el comportamiento inseguro — inyección, traversal, overflow o abuso de lógica.
- 3
Envía el payload a través de una solicitud normal y observa la reacción de la aplicación.
- 4
Itera hasta que la respuesta filtre datos, ejecute código del atacante o escale privilegios.
Ejemplo de código vulnerable
Vulnerable Java
Both of these examples use a statistical PRNG seeded with the current value of the system clock to generate a random number:
Random random = new Random(System.currentTimeMillis());
int accountID = random.nextInt(); Ejemplo de código seguro
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.
Lista de prevención
How to prevent CWE-338
- Implementation Use functions or hardware which use a hardware-based random number generation for all crypto. This is the recommended solution. Use CyptGenRandom on Windows, or hw_rand() on Linux.
Señales de detección
How to detect CWE-338
CWE-338
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Preguntas frecuentes ¿Qué es CWE-338?
¿Qué gravedad tiene CWE-338?
¿Qué lenguajes o plataformas se ven afectados por CWE-338?
¿Cómo puedo prevenir CWE-338?
¿Cómo detecta y corrige Plexicus CWE-338?
¿Dónde puedo aprender más sobre CWE-338?
Frequently asked questions
¿Qué es CWE-338?
This vulnerability occurs when software uses a pseudo-random number generator (PRNG) that is not cryptographically strong for security-sensitive operations, such as generating keys, tokens, or initialization vectors.
¿Qué gravedad tiene CWE-338?
MITRE califica la probabilidad de explotación como Media — la explotación es realista pero suele requerir condiciones específicas.
¿Qué lenguajes o plataformas se ven afectados por CWE-338?
MITRE no ha especificado plataformas afectadas para esta CWE — puede aplicar a la mayoría de los stacks de aplicaciones.
¿Cómo puedo prevenir CWE-338?
Use functions or hardware which use a hardware-based random number generation for all crypto. This is the recommended solution. Use CyptGenRandom on Windows, or hw_rand() on Linux.
¿Cómo detecta y corrige Plexicus CWE-338?
El motor SAST de Plexicus detecta la firma de flujo de datos para CWE-338 en cada commit. Cuando hay coincidencia, nuestro agente Codex Remedium abre un PR de corrección con el código corregido, las pruebas y un resumen de una línea para el revisor.
¿Dónde puedo aprender más sobre CWE-338?
MITRE publica la definición canónica en https://cwe.mitre.org/data/definitions/338.html. También puedes consultar la documentación de OWASP y NIST para guías relacionadas.
Debilidades relacionadas
Weaknesses related to CWE-338
CWE-330 Padre
Use of Insufficiently Random Values
This vulnerability occurs when an application uses random values that are not sufficiently unpredictable in security-sensitive operations,…
CWE-1204 Hermano
Generation of Weak Initialization Vector (IV)
This vulnerability occurs when software uses a weak or predictable Initialization Vector (IV) for cryptographic operations. Many…
CWE-1241 Hermano
Use of Predictable Algorithm in Random Number Generator
This vulnerability occurs when a device or application relies on a predictable algorithm to generate pseudo-random numbers, making the…
CWE-331 Hermano
Insufficient Entropy
This vulnerability occurs when a system's random number generator or algorithm lacks sufficient unpredictability, creating patterns or…
CWE-334 Hermano
Small Space of Random Values
This vulnerability occurs when a system uses a random number generator that produces too few possible values. Attackers can easily predict…
CWE-335 Hermano
Incorrect Usage of Seeds in Pseudo-Random Number Generator (PRNG)
This vulnerability occurs when a Pseudo-Random Number Generator (PRNG) is used, but its initial seed value is not handled securely or…
CWE-340 Hermano
Generation of Predictable Numbers or Identifiers
This vulnerability occurs when a system creates numbers or identifiers that are too easy to guess, undermining security mechanisms that…
CWE-344 Hermano
Use of Invariant Value in Dynamically Changing Context
This vulnerability occurs when code uses a fixed, unchanging value (like a hardcoded string, number, or reference) in a situation where…
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