CWE-336 Variant Draft

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.

Definition

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.
Auswirkungen in der Praxis

Real-world CVEs caused by CWE-336

  • CVE-2022-39218

    SDK for JavaScript app builder for serverless code uses the same fixed seed for a PRNG, allowing cryptography bypass

Wie Angreifer es ausnutzen

Angreiferpfad Schritt für Schritt

  1. 1

    The following code uses a statistical PRNG to generate account IDs.

  2. 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. 3

    This code attempts to generate a unique random identifier for a user's session.

  4. 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. 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).

Verwundbares Codebeispiel

Vulnerable Java

The following code uses a statistical PRNG to generate account IDs.

Verwundbar Java 
private static final long SEED = 1234567890;
  public int generateAccountID() {
  	Random random = new Random(SEED);
  	return random.nextInt();
  }
Sicheres Codebeispiel

Secure pseudo

Sicher 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-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.
Erkennungssignale

How to detect CWE-336

Automated Static Analysis High

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.)

Plexicus Auto-Fix

Plexicus erkennt CWE-336 automatisch und öffnet in unter 60 Sekunden einen Fix-PR.

Codex Remedium scannt jeden Commit, identifiziert genau diese Schwachstelle und liefert einen reviewer-ready Pull Request mit dem Patch. Keine Tickets. Keine Hand-offs.

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Häufig gestellte Fragen

Frequently asked questions

Was ist CWE-336?

This vulnerability occurs when a Pseudo-Random Number Generator (PRNG) is repeatedly initialized with the same starting seed value.

Wie gravierend ist CWE-336?

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-336 betroffen?

MITRE hat für diese CWE keine betroffenen Plattformen spezifiziert — sie kann in den meisten Anwendungs-Stacks auftreten.

Wie kann ich CWE-336 verhindern?

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.

Wie erkennt und behebt Plexicus CWE-336?

Die SAST-Engine von Plexicus erkennt die Datenfluss-Signatur von CWE-336 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-336?

MITRE veröffentlicht die kanonische Definition unter https://cwe.mitre.org/data/definitions/336.html. Für ergänzende Hinweise kannst du auch die OWASP- und NIST-Dokumentation heranziehen.

Verwandte Schwachstellen

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 Sibling

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 Sibling

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…

Ressourcen

Further reading

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