CWE-325 Base Draft

Missing Cryptographic Step

This vulnerability occurs when a software implementation skips a critical step in a cryptographic process, resulting in security that is significantly weaker than the intended algorithm provides.

Definition

What is CWE-325?

This vulnerability occurs when a software implementation skips a critical step in a cryptographic process, resulting in security that is significantly weaker than the intended algorithm provides.
Cryptographic algorithms are designed as a sequence of specific, interdependent steps. Each step serves a purpose, such as ensuring randomness, preventing pattern analysis, or binding data together securely. When a developer omits one of these steps—whether during key generation, encryption, decryption, or integrity verification—the entire cryptographic operation becomes fragile. The resulting system may appear to function normally but can be easily broken by attackers using well-known techniques, completely undermining the promised security. This flaw often stems from using incomplete code samples, misunderstanding algorithm specifications, or attempting to 'optimize' performance by removing so-called 'unnecessary' operations. To prevent it, developers should rely on reputable, high-level cryptographic libraries rather than implementing algorithms from scratch. Always follow the official algorithm specification or RFC meticulously, and use established test vectors to verify that every required step is correctly executed in the proper order.
Real-world impact

Real-world CVEs caused by CWE-325

  • CVE-2001-1585

    Missing challenge-response step allows authentication bypass using public key.

How attackers exploit it

Step-by-step attacker path

  1. 1

    The example code is taken from the HMAC engine inside the buggy OpenPiton SoC of HACK@DAC'21 [REF-1358]. HAMC is a message authentication code (MAC) that uses both a hash and a secret crypto key. The HMAC engine in HACK@DAC SoC uses the SHA-256 module for the calculation of the HMAC for 512 bits messages.

  2. 2

    However, this HMAC engine cannot handle messages that are longer than 512 bits. Moreover, a complete HMAC will contain an iterate hash function that breaks up a message into blocks of a fixed size and iterates over them with a compression function (e.g., SHA-256). Therefore, the implementation of the HMAC in OpenPiton SoC is incomplete. Such HMAC engines will not be used in real-world applications as the messages will usually be longer than 512 bits. For instance, OpenTitan offers a comprehensive HMAC implementation that utilizes a FIFO for temporarily storing the truncated message, as detailed in [REF-1359].

  3. 3

    To mitigate this, implement the iterative function to break up a message into blocks of a fixed size.

Vulnerable code example

Vulnerable Verilog

The example code is taken from the HMAC engine inside the buggy OpenPiton SoC of HACK@DAC'21 [REF-1358]. HAMC is a message authentication code (MAC) that uses both a hash and a secret crypto key. The HMAC engine in HACK@DAC SoC uses the SHA-256 module for the calculation of the HMAC for 512 bits messages.

Vulnerable Verilog 
**logic [511:0] bigData;** 
 ...

 hmac hmac(

```
   .clk_i(clk_i),
   .rst_ni(rst_ni && ~rst_4),
   .init_i(startHash && ~startHash_r),
   .key_i(key),
   .ikey_hash_i(ikey_hash), 
   .okey_hash_i(okey_hash), 
   .key_hash_bypass_i(key_hash_bypass),
```
.message_i(bigData),** 
   .hash_o(hash),
   .ready_o(ready),
   .hash_valid_o(hashValid)
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-325

  • Architecture Use safe-by-default frameworks and APIs that prevent the unsafe pattern from being expressible.
  • Implementation Validate input at trust boundaries; use allowlists, not denylists.
  • Implementation Apply the principle of least privilege to credentials, file paths, and runtime permissions.
  • Testing Cover this weakness in CI: SAST rules + targeted unit tests for the data flow.
  • Operation Monitor logs for the runtime signals listed in the next section.
Detection signals

How to detect CWE-325

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-325 and opens a fix PR in under 60 seconds.

Codex Remedium scans every commit, identifies this exact weakness, and ships a reviewer-ready pull request with the patch. No tickets. No hand-offs.

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Frequently asked questions

Frequently asked questions

What is CWE-325?

This vulnerability occurs when a software implementation skips a critical step in a cryptographic process, resulting in security that is significantly weaker than the intended algorithm provides.

How serious is CWE-325?

MITRE has not published a likelihood-of-exploit rating for this weakness. Treat it as medium-impact until your threat model proves otherwise.

What languages or platforms are affected by CWE-325?

MITRE lists the following affected platforms: Not Technology-Specific.

How can I prevent CWE-325?

Use safe-by-default frameworks, validate untrusted input at trust boundaries, and apply the principle of least privilege. Cover the data-flow signature in CI with SAST.

How does Plexicus detect and fix CWE-325?

Plexicus's SAST engine matches the data-flow signature for CWE-325 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-325?

MITRE publishes the canonical definition at https://cwe.mitre.org/data/definitions/325.html. You can also reference OWASP and NIST documentation for adjacent guidance.

Related weaknesses

Weaknesses related to CWE-325

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CWE-253 Sibling

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CWE-296 Sibling

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CWE-304 Sibling

Missing Critical Step in Authentication

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CWE-329 Sibling

Generation of Predictable IV with CBC Mode

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CWE-358 Sibling

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Resources

Further reading

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