CWE-435 Pillar Draft

Improper Interaction Between Multiple Correctly-Behaving Entities

This weakness occurs when individually secure components interact in unexpected ways within a larger system, creating new security flaws that weren't present in isolation.

Definition

What is CWE-435?

This weakness occurs when individually secure components interact in unexpected ways within a larger system, creating new security flaws that weren't present in isolation.
Modern software often integrates multiple independent components, libraries, or services. While each component may function correctly and securely on its own, their combination can create unintended, emergent behaviors at the system level. These new behaviors are not a failure of any single component, but a result of unanticipated interactions between them. For developers, this means secure design must extend beyond individual modules to include their integration points. Failing to model how components exchange data, share resources, or handle errors together can introduce vulnerabilities that are invisible during unit testing. The security of the whole system depends on understanding these interactions as much as the security of its parts.
Real-world impact

Real-world CVEs caused by CWE-435

  • CVE-2002-0485

    Anti-virus product allows bypass via Content-Type and Content-Disposition headers that are mixed case, which are still processed by some clients.

  • CVE-2003-0411

    chain: Code was ported from a case-sensitive Unix platform to a case-insensitive Windows platform where filetype handlers treat .jsp and .JSP as different extensions. JSP source code may be read because .JSP defaults to the filetype "text".

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-435

  • 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-435

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-435?

This weakness occurs when individually secure components interact in unexpected ways within a larger system, creating new security flaws that weren't present in isolation.

How serious is CWE-435?

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-435?

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

How can I prevent CWE-435?

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-435?

Plexicus's SAST engine matches the data-flow signature for CWE-435 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-435?

MITRE publishes the canonical definition at https://cwe.mitre.org/data/definitions/435.html. You can also reference OWASP and NIST documentation for adjacent guidance.

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Resources

Further reading

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