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-336 Variante Brouillon
Same Seed in Pseudo-Random Number Generator (PRNG)
This vulnerability occurs when a Pseudo-Random Number Generator (PRNG) is repeatedly initialized with the same starting seed value.
Définition
What is CWE-336?
This vulnerability occurs when a Pseudo-Random Number Generator (PRNG) is repeatedly initialized with the same starting seed value.
PRNGs are deterministic, meaning that if you start them from the same seed, they will produce an identical sequence of 'random' numbers every single time. This predictability breaks the core assumption of randomness that many security features rely on, such as session tokens, cryptographic keys, or password reset tokens.
If an attacker discovers or can reasonably guess the seed—for example, if it's a hard-coded value, a simple timestamp, or another predictable source—they can pre-calculate or replicate the entire output sequence. This allows them to anticipate future random values, bypass security controls, impersonate users, or compromise encrypted data that depends on those numbers being truly unpredictable.
Impact réel
Real-world CVEs caused by CWE-336
-
SDK for JavaScript app builder for serverless code uses the same fixed seed for a PRNG, allowing cryptography bypass
Comment les attaquants l'exploitent
Parcours de l'attaquant étape par étape
- 1
The following code uses a statistical PRNG to generate account IDs.
- 2
Because the program uses the same seed value for every invocation of the PRNG, its values are predictable, making the system vulnerable to attack.
- 3
This code attempts to generate a unique random identifier for a user's session.
- 4
Because the seed for the PRNG is always the user's ID, the session ID will always be the same. An attacker could thus predict any user's session ID and potentially hijack the session.
- 5
If the user IDs are generated sequentially, or otherwise restricted to a narrow range of values, then this example also exhibits a Small Seed Space (CWE-339).
Exemple de code vulnérable
Vulnerable Java
The following code uses a statistical PRNG to generate account IDs.
private static final long SEED = 1234567890;
public int generateAccountID() {
Random random = new Random(SEED);
return random.nextInt();
} 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-336
- Architecture and Design Do not reuse PRNG seeds. Consider a PRNG that periodically re-seeds itself as needed from a high quality pseudo-random output, such as hardware devices.
- Architecture and Design / Requirements Use products or modules that conform to FIPS 140-2 [REF-267] to avoid obvious entropy problems, or use the more recent FIPS 140-3 [REF-1192] if possible.
Signaux de détection
How to detect CWE-336
CWE-336
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.
Questions fréquentes Qu'est-ce que CWE-336 ?
Quelle est la gravité de CWE-336 ?
Quels langages ou plateformes sont affectés par CWE-336 ?
Comment puis-je prévenir CWE-336 ?
Comment Plexicus détecte et corrige CWE-336 ?
Où puis-je en savoir plus sur CWE-336 ?
Frequently asked questions
Qu'est-ce que CWE-336 ?
This vulnerability occurs when a Pseudo-Random Number Generator (PRNG) is repeatedly initialized with the same starting seed value.
Quelle est la gravité de CWE-336 ?
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-336 ?
MITRE n'a pas spécifié les plateformes affectées pour ce CWE — il peut s'appliquer à la plupart des stacks applicatives.
Comment puis-je prévenir CWE-336 ?
Do not reuse PRNG seeds. Consider a PRNG that periodically re-seeds itself as needed from a high quality pseudo-random output, such as hardware devices. Use products or modules that conform to FIPS 140-2 [REF-267] to avoid obvious entropy problems, or use the more recent FIPS 140-3 [REF-1192] if possible.
Comment Plexicus détecte et corrige CWE-336 ?
Le moteur SAST de Plexicus reconnaît la signature de flux de données de CWE-336 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-336 ?
MITRE publie la définition canonique à https://cwe.mitre.org/data/definitions/336.html. Vous pouvez également consulter la documentation OWASP et NIST pour des conseils adjacents.
Faiblesses associées
Weaknesses related to CWE-336
CWE-335 Parent
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-337 Frère
Predictable Seed in Pseudo-Random Number Generator (PRNG)
This vulnerability occurs when a Pseudo-Random Number Generator (PRNG) uses an easily guessable starting value, like the current system…
CWE-339 Frère
Small Seed Space in PRNG
This vulnerability occurs when a Pseudo-Random Number Generator (PRNG) uses a seed that has too few possible values, making it easy for an…
Ressources
Further reading
- MITRE — CWE-336 officiel https://cwe.mitre.org/data/definitions/336.html
- FIPS PUB 140-2: SECURITY REQUIREMENTS FOR CRYPTOGRAPHIC MODULES https://csrc.nist.gov/files/pubs/fips/140-2/upd2/final/docs/fips1402.pdf
- FIPS PUB 140-3: SECURITY REQUIREMENTS FOR CRYPTOGRAPHIC MODULES https://csrc.nist.gov/publications/detail/fips/140/3/final
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