CWE-1204: Generation of Weak Initialization Vector (IV)

Definition

What is CWE-1204?

This vulnerability occurs when software uses a weak or predictable Initialization Vector (IV) for cryptographic operations. Many encryption algorithms require IVs to be both unique and unpredictable to ensure security, and failing to meet these requirements can compromise the entire encryption process.

Certain encryption methods, like block ciphers in specific modes, rely heavily on strong Initialization Vectors. The IV must be both unique (never reused with the same key) and unpredictable (random) to prevent attackers from deducing patterns or recovering plaintext. If the IV generation is flawed—due to a bug, a poor random source, or a reused value—the cryptographic protection can be significantly weakened. In practice, attacking a weak IV is often easier than breaking the core cipher. Attackers can exploit predictable or repeated IVs to perform decryption, reveal data patterns, or bypass security entirely. Therefore, developers must ensure their IV generation adheres strictly to the requirements of the specific cryptographic primitive being used.

Auswirkungen in der Praxis

Real-world CVEs caused by CWE-1204

CVE-2020-1472

ZeroLogon vulnerability - use of a static IV of all zeroes in AES-CFB8 mode
CVE-2011-3389

BEAST attack in SSL 3.0 / TLS 1.0. In CBC mode, chained initialization vectors are non-random, allowing decryption of HTTPS traffic using a chosen plaintext attack.
CVE-2001-0161

wireless router does not use 6 of the 24 bits for WEP encryption, making it easier for attackers to decrypt traffic
CVE-2001-0160

WEP card generates predictable IV values, making it easier for attackers to decrypt traffic
CVE-2017-3225

device bootloader uses a zero initialization vector during AES-CBC
CVE-2016-6485

crypto framework uses PHP rand function - which is not cryptographically secure - for an initialization vector
CVE-2014-5386

encryption routine does not seed the random number generator, causing the same initialization vector to be generated repeatedly
CVE-2020-5408

encryption functionality in an authentication framework uses a fixed null IV with CBC mode, allowing attackers to decrypt traffic in applications that use this functionality

Wie Angreifer es ausnutzen

Angreiferpfad Schritt für Schritt

1
In the following examples, CBC mode is used when encrypting data:
2
In both of these examples, the initialization vector (IV) is always a block of zeros. This makes the resulting cipher text much more predictable and susceptible to a dictionary attack.
3
The Wired Equivalent Privacy (WEP) protocol used in the 802.11 wireless standard only supported 40-bit keys, and the IVs were only 24 bits, increasing the chances that the same IV would be reused for multiple messages. The IV was included in plaintext as part of the packet, making it directly observable to attackers. Only 5000 messages are needed before a collision occurs due to the "birthday paradox" [REF-1176]. Some implementations would reuse the same IV for each packet. This IV reuse made it much easier for attackers to recover plaintext from two packets with the same IV, using well-understood attacks, especially if the plaintext was known for one of the packets [REF-1175].

Verwundbares Codebeispiel

Vulnerable C

In the following examples, CBC mode is used when encrypting data:

Verwundbar C

EVP_CIPHER_CTX ctx;
  char key[EVP_MAX_KEY_LENGTH];
  char iv[EVP_MAX_IV_LENGTH];
  RAND_bytes(key, b);
  memset(iv,0,EVP_MAX_IV_LENGTH);
  EVP_EncryptInit(&ctx,EVP_bf_cbc(), key,iv);

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-1204

Implementation Different cipher modes have different requirements for their IVs. When choosing and implementing a mode, it is important to understand those requirements in order to keep security guarantees intact. Generally, it is safest to generate a random IV, since it will be both unpredictable and have a very low chance of being non-unique. IVs do not have to be kept secret, so if generating duplicate IVs is a concern, a list of already-used IVs can be kept and checked against. NIST offers recommendations on generation of IVs for modes of which they have approved. These include options for when random IVs are not practical. For CBC, CFB, and OFB, see [REF-1175]; for GCM, see [REF-1178].

Erkennungssignale

How to detect CWE-1204

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.

CWE-1204

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Häufig gestellte Fragen

Frequently asked questions

Was ist CWE-1204?

This vulnerability occurs when software uses a weak or predictable Initialization Vector (IV) for cryptographic operations. Many encryption algorithms require IVs to be both unique and unpredictable to ensure security, and failing to meet these requirements can compromise the entire encryption process.

Wie gravierend ist CWE-1204?

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-1204 betroffen?

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

Wie kann ich CWE-1204 verhindern?

Different cipher modes have different requirements for their IVs. When choosing and implementing a mode, it is important to understand those requirements in order to keep security guarantees intact. Generally, it is safest to generate a random IV, since it will be both unpredictable and have a very low chance of being non-unique. IVs do not have to be kept secret, so if generating duplicate IVs is a concern, a list of already-used IVs can be kept and checked against. NIST offers…

Wie erkennt und behebt Plexicus CWE-1204?

Die SAST-Engine von Plexicus erkennt die Datenfluss-Signatur von CWE-1204 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-1204?

MITRE veröffentlicht die kanonische Definition unter https://cwe.mitre.org/data/definitions/1204.html. Für ergänzende Hinweise kannst du auch die OWASP- und NIST-Dokumentation heranziehen.

Verwandte Schwachstellen

Weaknesses related to CWE-1204

CWE-330 Parent

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Generation of Weak Initialization Vector (IV)

What is CWE-1204?

Real-world CVEs caused by CWE-1204

Angreiferpfad Schritt für Schritt

Vulnerable C

Secure pseudo

How to prevent CWE-1204

How to detect CWE-1204

Don't catalog this weakness. Prove it's reachable.

Frequently asked questions

Weaknesses related to CWE-1204

Use of Insufficiently Random Values

Use of Predictable Algorithm in Random Number Generator

Insufficient Entropy

Small Space of Random Values

Incorrect Usage of Seeds in Pseudo-Random Number Generator (PRNG)

Use of Cryptographically Weak Pseudo-Random Number Generator (PRNG)

Generation of Predictable Numbers or Identifiers

Use of Invariant Value in Dynamically Changing Context

Generation of Predictable IV with CBC Mode

Further reading

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Sample evidence handover

Server-Side Request Forgery in `webhooks/receiver`