CWE-573 Class Draft

Improper Following of Specification by Caller

This weakness occurs when software fails to properly follow the documented rules, protocols, or requirements of an external component it uses, such as a library, API, framework, or platform.

Definition

What is CWE-573?

This weakness occurs when software fails to properly follow the documented rules, protocols, or requirements of an external component it uses, such as a library, API, framework, or platform.
When your code calls an external function—like an API method, a library routine, or a system call—it must play by that component's rules. Ignoring required parameter formats, sequence of operations, state assumptions, or error handling protocols can cause the external component to behave in unexpected and insecure ways. This mismatch between expected and actual usage is the core of the vulnerability. For developers, this means carefully reading and adhering to the official specifications, SDK documentation, or API contracts for any external dependency. Assume that deviations, even if they seem to work during testing, can introduce subtle bugs, stability issues, or security gaps that attackers might exploit to bypass controls, crash the system, or access unauthorized data.
Real-world impact

Real-world CVEs caused by CWE-573

  • CVE-2006-7140

    Crypto implementation removes padding when it shouldn't, allowing forged signatures

  • CVE-2006-4339

    Crypto implementation removes padding when it shouldn't, allowing forged signatures

How attackers exploit it

Step-by-step attacker path

  1. 1

    Identify a code path that handles untrusted input without validation.

  2. 2

    Craft a payload that exercises the unsafe behavior — injection, traversal, overflow, or logic abuse.

  3. 3

    Deliver the payload through a normal request and observe the application's reaction.

  4. 4

    Iterate until the response leaks data, executes attacker code, or escalates privileges.

Vulnerable code example

Vulnerable pseudo

MITRE has not published a code example for this CWE. The pattern below is illustrative — see Resources for canonical references.

Vulnerable pseudo 
// Example pattern — see MITRE for the canonical references.
function handleRequest(input) {
  // Untrusted input flows directly into the sensitive sink.
  return executeUnsafe(input);
}
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-573

  • 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-573

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

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Frequently asked questions

Frequently asked questions

What is CWE-573?

This weakness occurs when software fails to properly follow the documented rules, protocols, or requirements of an external component it uses, such as a library, API, framework, or platform.

How serious is CWE-573?

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-573?

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

How can I prevent CWE-573?

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-573?

Plexicus's SAST engine matches the data-flow signature for CWE-573 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-573?

MITRE publishes the canonical definition at https://cwe.mitre.org/data/definitions/573.html. You can also reference OWASP and NIST documentation for adjacent guidance.

Related weaknesses

Weaknesses related to CWE-573

CWE-710 Parent

Improper Adherence to Coding Standards

This weakness occurs when developers don't consistently follow established coding standards and best practices, which can introduce…

CWE-1041 Sibling

Use of Redundant Code

This weakness occurs when a codebase contains identical or nearly identical logic duplicated across multiple functions, methods, or…

CWE-1044 Sibling

Architecture with Number of Horizontal Layers Outside of Expected Range

This occurs when a software system is built with either too many or too few distinct architectural layers, falling outside a recommended…

CWE-1048 Sibling

Invokable Control Element with Large Number of Outward Calls

This weakness occurs when a single function, method, or callable code block makes an excessively high number of calls to other objects or…

CWE-1059 Sibling

Insufficient Technical Documentation

This weakness occurs when a software or hardware product lacks comprehensive technical documentation. Missing or incomplete details about…

CWE-1061 Sibling

Insufficient Encapsulation

This weakness occurs when a software component exposes too much of its internal workings, such as data structures or implementation logic.…

CWE-1065 Sibling

Runtime Resource Management Control Element in a Component Built to Run on Application Servers

This weakness occurs when an application built to run on a managed application server bypasses the server's high-level APIs and instead…

CWE-1066 Sibling

Missing Serialization Control Element

This weakness occurs when a class or data structure is marked as serializable but lacks the required control methods to properly handle…

CWE-1068 Sibling

Inconsistency Between Implementation and Documented Design

This weakness occurs when the actual code implementation deviates from the intended design described in its official documentation,…

Resources

Further reading

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