CWE-247 Base Deprecated

DEPRECATED: Reliance on DNS Lookups in a Security Decision

This deprecated entry has been merged into CWE-350: Reliance on Reverse DNS Resolution for a Security-Critical Action. All related content has been moved to that primary weakness entry.

Definition

What is CWE-247?

This deprecated entry has been merged into CWE-350: Reliance on Reverse DNS Resolution for a Security-Critical Action. All related content has been moved to that primary weakness entry.
This entry was retired because it duplicated the core issue described in CWE-350: using DNS lookups, particularly reverse DNS (rDNS), to make security decisions like authentication or access control. DNS records are inherently easy to spoof or poison, making them an unreliable source for verifying identity or trust. Relying on them creates a significant vulnerability where an attacker can manipulate DNS to bypass security checks. For current guidance, developers should reference CWE-350 directly. The main takeaway is to never use DNS hostnames or IP address lookups alone to authenticate users, authorize actions, or filter input. Instead, implement proper authentication mechanisms like certificates, tokens, or other cryptographic methods that cannot be easily forged through DNS manipulation.
Real-world impact

Real-world CVEs caused by CWE-247

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

    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-247

  • 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-247

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-247?

This deprecated entry has been merged into CWE-350: Reliance on Reverse DNS Resolution for a Security-Critical Action. All related content has been moved to that primary weakness entry.

How serious is CWE-247?

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-247?

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

How can I prevent CWE-247?

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-247?

Plexicus's SAST engine matches the data-flow signature for CWE-247 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-247?

MITRE publishes the canonical definition at https://cwe.mitre.org/data/definitions/247.html. You can also reference OWASP and NIST documentation for adjacent guidance.

Related weaknesses

Weaknesses related to CWE-247

No related weaknesses indexed for this CWE.

Resources

Further reading

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