CWE-323 Reusing a Nonce or IV

Coverage: 5 rules in the SiteShadow rule registry target this CWE (registry v2.0.0). Regex 5 Also: Taint and heuristic analyzers may also detect related flows (see coverage for the authoritative list) Registry tagging shows intent, for sample-level behaviour and benchmarked gaps see known gaps.

What this means

SiteShadow flagged nonce/IV reuse across encryptions. Many modern crypto schemes require a unique nonce/IV per message; reusing it can break confidentiality (and sometimes integrity).

Why it matters

Nonce or IV reuse can break encryption guarantees.

• With some modes, reuse can allow attackers to recover plaintext relationships or even keys.
• This is a common source of "crypto looks correct but fails catastrophically."

Safer examples

1) Use libraries that manage nonces/IVs safely

Prefer high-level APIs that generate nonces and return them with ciphertext.

2) Prefer AEAD modes

Use AES‑GCM / ChaCha20‑Poly1305 and ensure nonces are unique per key.

3) If you must manage nonces yourself, enforce uniqueness

Use a counter-based nonce or random nonces with collision resistance, and never repeat for the same key.

How SiteShadow detects it (high level)

• Flags crypto code where the same nonce/IV variable is reused across encryptions.
• Detects suspicious "fixed nonce/IV" patterns in AEAD/CBC contexts.

References

• CWE-323: https://cwe.mitre.org/data/definitions/323.html

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