CWE-338 Base Draft Medium likelihood

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…

Definition

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.
Auswirkungen in der Praxis

Real-world CVEs caused by CWE-338

  • CVE-2021-3692

    PHP framework uses mt_rand() function (Marsenne Twister) when generating tokens

  • CVE-2009-3278

    Crypto product uses rand() library function to generate a recovery key, making it easier to conduct brute force attacks.

  • CVE-2009-3238

    Random number generator can repeatedly generate the same value.

  • CVE-2009-2367

    Web application generates predictable session IDs, allowing session hijacking.

  • CVE-2008-0166

    SSL library uses a weak random number generator that only generates 65,536 unique keys.

Wie Angreifer es ausnutzen

Angreiferpfad Schritt für Schritt

  1. 1

    Identifiziere einen Codepfad, der nicht vertrauenswürdige Eingaben ohne Validierung verarbeitet.

  2. 2

    Erzeuge eine Payload, die das unsichere Verhalten auslöst — Injection, Traversal, Overflow oder Logik-Missbrauch.

  3. 3

    Liefere die Payload über einen normalen Request aus und beobachte die Reaktion der Anwendung.

  4. 4

    Iteriere, bis die Antwort Daten preisgibt, Angreifer-Code ausführt oder Berechtigungen eskaliert.

Verwundbares Codebeispiel

Vulnerable Java

Both of these examples use a statistical PRNG seeded with the current value of the system clock to generate a random number:

Verwundbar Java 
Random random = new Random(System.currentTimeMillis());
  int accountID = 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-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.
Erkennungssignale

How to detect CWE-338

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-338 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.

Demo anfordern Plexicus kostenlos testen
Häufig gestellte Fragen

Frequently asked questions

Was ist 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.

Wie gravierend ist CWE-338?

MITRE stuft die Exploit-Wahrscheinlichkeit als mittel ein — eine Ausnutzung ist realistisch, erfordert aber meist bestimmte Bedingungen.

Welche Sprachen oder Plattformen sind von CWE-338 betroffen?

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

Wie kann ich CWE-338 verhindern?

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.

Wie erkennt und behebt Plexicus CWE-338?

Die SAST-Engine von Plexicus erkennt die Datenfluss-Signatur von CWE-338 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-338?

MITRE veröffentlicht die kanonische Definition unter https://cwe.mitre.org/data/definitions/338.html. Für ergänzende Hinweise kannst du auch die OWASP- und NIST-Dokumentation heranziehen.

Verwandte Schwachstellen

Weaknesses related to CWE-338

CWE-330 Parent

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 Sibling

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 Sibling

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 Sibling

Insufficient Entropy

This vulnerability occurs when a system's random number generator or algorithm lacks sufficient unpredictability, creating patterns or…

CWE-334 Sibling

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 Sibling

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 Sibling

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 Sibling

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…

Ressourcen

Further reading

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