CWE-323 Base Incomplete High likelihood

Reusing a Nonce, Key Pair in Encryption

This vulnerability occurs when a cryptographic nonce or key pair is reused, compromising the security of the encrypted data.

Definition

What is CWE-323?

This vulnerability occurs when a cryptographic nonce or key pair is reused, compromising the security of the encrypted data.
In cryptography, a nonce (number used once) is a random or pseudo-random value that should be used for a single encryption session or transaction. Reusing it, or reusing the same key pair in a similar context, can allow attackers to decrypt messages, forge authentication, or break the encryption scheme entirely. This fundamentally undermines the security guarantees that modern encryption is designed to provide. To prevent this, developers must ensure nonces and ephemeral key pairs are generated uniquely for every single operation. Implement systems that securely manage state to guarantee no value is repeated, and prefer using well-vetted cryptographic libraries that handle this automatically, rather than attempting custom implementations.
Real-world impact

Real-world CVEs caused by CWE-323

No public CVE references are linked to this CWE in MITRE's catalog yet.

How attackers exploit it

Step-by-step attacker path

  1. 1

    This code takes a password, concatenates it with a nonce, then encrypts it before sending over a network:

  2. 2

    Because the nonce used is always the same, an attacker can impersonate a trusted party by intercepting and resending the encrypted password. This attack avoids the need to learn the unencrypted password.

  3. 3

    This code sends a command to a remote server, using an encrypted password and nonce to prove the command is from a trusted party:

  4. 4

    Once again the nonce used is always the same. An attacker may be able to replay previous legitimate commands or execute new arbitrary commands.

Vulnerable code example

Vulnerable C

This code takes a password, concatenates it with a nonce, then encrypts it before sending over a network:

Vulnerable C 
void encryptAndSendPassword(char *password){
  	char *nonce = "bad";
  	...
  	char *data = (unsigned char*)malloc(20);
  	int para_size = strlen(nonce) + strlen(password);
  	char *paragraph = (char*)malloc(para_size);
  	SHA1((const unsigned char*)paragraph,parsize,(unsigned char*)data);
  	sendEncryptedData(data)
  }
Secure code example

Secure pseudo

Secure 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.
Prevention checklist

How to prevent CWE-323

  • Implementation Refuse to reuse nonce values.
  • Implementation Use techniques such as requiring incrementing, time based and/or challenge response to assure uniqueness of nonces.
Detection signals

How to detect CWE-323

SAST High

Run static analysis (SAST) on the codebase looking for the unsafe pattern in the data flow.

DAST Moderate

Run dynamic application security testing against the live endpoint.

Runtime Moderate

Watch runtime logs for unusual exception traces, malformed input, or authorization bypass attempts.

Code review Moderate

Code review: flag any new code that handles input from this surface without using the validated framework helpers.

Plexicus auto-fix

Plexicus auto-detects CWE-323 and opens a fix PR in under 60 seconds.

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Frequently asked questions

Frequently asked questions

What is CWE-323?

This vulnerability occurs when a cryptographic nonce or key pair is reused, compromising the security of the encrypted data.

How serious is CWE-323?

MITRE rates the likelihood of exploit as High — this weakness is actively exploited in the wild and should be prioritized for remediation.

What languages or platforms are affected by CWE-323?

MITRE has not specified affected platforms for this CWE — it can apply across most application stacks.

How can I prevent CWE-323?

Refuse to reuse nonce values. Use techniques such as requiring incrementing, time based and/or challenge response to assure uniqueness of nonces.

How does Plexicus detect and fix CWE-323?

Plexicus's SAST engine matches the data-flow signature for CWE-323 on every commit. When a match is found, our Codex Remedium agent opens a fix PR with the corrected code, tests, and a one-line summary for the reviewer.

Where can I learn more about CWE-323?

MITRE publishes the canonical definition at https://cwe.mitre.org/data/definitions/323.html. You can also reference OWASP and NIST documentation for adjacent guidance.

Related weaknesses

Weaknesses related to CWE-323

CWE-344 Parent

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-587 Sibling

Assignment of a Fixed Address to a Pointer

This vulnerability occurs when code explicitly assigns a hardcoded memory address to a pointer, instead of using a dynamic or null value.

CWE-798 Sibling

Use of Hard-coded Credentials

This vulnerability occurs when software contains built-in, unchangeable authentication secrets like passwords or encryption keys within…

Resources

Further reading

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