CWE-334 Base Draft

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 or guess these values through brute force attacks.

Definition

What is CWE-334?

This vulnerability occurs when a system uses a random number generator that produces too few possible values. Attackers can easily predict or guess these values through brute force attacks.
When an application relies on random values for security—like generating session tokens, encryption keys, or password reset codes—using a random source with a small output space is a critical flaw. For example, a random number generator that only produces 65,536 possible values (16 bits) is trivial for an automated script to exhaustively try all combinations. This directly undermines security mechanisms designed to be unpredictable. To prevent this, developers must ensure their random value generators have an output space large enough to resist brute-force attempts for the required lifespan of the secret. This typically means using cryptographically secure pseudo-random number generators (CSPRNGs) that produce values with at least 128 bits of entropy. Always match the randomness strength to the sensitivity of the operation it protects.
Auswirkungen in der Praxis

Real-world CVEs caused by CWE-334

  • CVE-2002-0583

    Product uses 5 alphanumeric characters for filenames of expense claim reports, stored under web root.

  • CVE-2002-0903

    Product uses small number of random numbers for a code to approve an action, and also uses predictable new user IDs, allowing attackers to hijack new accounts.

  • CVE-2003-1230

    SYN cookies implementation only uses 32-bit keys, making it easier to brute force ISN.

  • CVE-2004-0230

    Complex predictability / randomness (reduced space).

Wie Angreifer es ausnutzen

Angreiferpfad Schritt für Schritt

  1. 1

    The following XML example code is a deployment descriptor for a Java web application deployed on a Sun Java Application Server. This deployment descriptor includes a session configuration property for configuring the session ID length.

  2. 2

    This deployment descriptor has set the session ID length for this Java web application to 8 bytes (or 64 bits). The session ID length for Java web applications should be set to 16 bytes (128 bits) to prevent attackers from guessing and/or stealing a session ID and taking over a user's session.

  3. 3

    Note for most application servers including the Sun Java Application Server the session ID length is by default set to 128 bits and should not be changed. And for many application servers the session ID length cannot be changed from this default setting. Check your application server documentation for the session ID length default setting and configuration options to ensure that the session ID length is set to 128 bits.

Verwundbares Codebeispiel

Vulnerable XML

The following XML example code is a deployment descriptor for a Java web application deployed on a Sun Java Application Server. This deployment descriptor includes a session configuration property for configuring the session ID length.

Verwundbar XML 
<sun-web-app>
  		...
  		<session-config>
  				<session-properties>
  					<property name="idLengthBytes" value="8">
  						<description>The number of bytes in this web module's session ID.</description>
  					</property>
  				</session-properties>
  		</session-config>
  		...
  </sun-web-app>
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-334

  • Architecture and Design / Requirements Use products or modules that conform to FIPS 140-2 [REF-267] to avoid obvious entropy problems. Consult FIPS 140-2 Annex C ("Approved Random Number Generators").
Erkennungssignale

How to detect CWE-334

SAST High

Führe statische Analyse (SAST) auf der Codebasis aus und suche im Datenfluss nach dem unsicheren Muster.

DAST Moderate

Führe dynamische Application-Security-Tests gegen den Live-Endpoint aus.

Runtime Moderate

Beobachte Runtime-Logs auf ungewöhnliche Exception-Traces, fehlerhafte Eingaben oder Versuche, Autorisierung zu umgehen.

Code review Moderate

Code Review: Markiere jeden neuen Code, der Eingaben von dieser Oberfläche ohne validierte Framework-Helper verarbeitet.

Plexicus Auto-Fix

Plexicus erkennt CWE-334 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-334?

This vulnerability occurs when a system uses a random number generator that produces too few possible values. Attackers can easily predict or guess these values through brute force attacks.

Wie gravierend ist CWE-334?

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-334 betroffen?

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

Wie kann ich CWE-334 verhindern?

Use products or modules that conform to FIPS 140-2 [REF-267] to avoid obvious entropy problems. Consult FIPS 140-2 Annex C ("Approved Random Number Generators").

Wie erkennt und behebt Plexicus CWE-334?

Die SAST-Engine von Plexicus erkennt die Datenfluss-Signatur von CWE-334 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-334?

MITRE veröffentlicht die kanonische Definition unter https://cwe.mitre.org/data/definitions/334.html. Für ergänzende Hinweise kannst du auch die OWASP- und NIST-Dokumentation heranziehen.

Verwandte Schwachstellen

Weaknesses related to CWE-334

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-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-338 Sibling

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…

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…

CWE-6 Child

J2EE Misconfiguration: Insufficient Session-ID Length

This vulnerability occurs when a J2EE application uses session identifiers that are too short, making them easier for attackers to predict…

Ressourcen

Further reading

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