CWE-348 Base Draft

Use of Less Trusted Source

This vulnerability occurs when a system has access to multiple sources for the same critical data, but it chooses to rely on the less secure or less trustworthy one. This creates a security gap…

Definition

What is CWE-348?

This vulnerability occurs when a system has access to multiple sources for the same critical data, but it chooses to rely on the less secure or less trustworthy one. This creates a security gap because the system ignores better-protected alternatives that offer stronger verification or are harder for attackers to compromise.
Think of this flaw as a developer choosing to trust a rumor from an anonymous tip line over an official, signed document from a verified authority—even though both claim to state the same fact. The core issue isn't about missing data, but about making a poor choice between available sources. This often happens in code that fetches configuration, license keys, or critical parameters from multiple locations (like a local file, a network service, and a hardware security module) but defaults to the most convenient, rather than the most secure, option. To prevent this, your code should implement a clear trust hierarchy. Always design your system to prefer and require the most authoritative source—the one with the strongest cryptographic verification, integrity checks, or tamper resistance. This means explicitly validating the source before trusting its data and failing securely if the high-trust source is unavailable, rather than silently falling back to a weaker alternative that an attacker could easily manipulate.
Real-world impact

Real-world CVEs caused by CWE-348

  • CVE-2001-0860

    Product uses IP address provided by a client, instead of obtaining it from the packet headers, allowing easier spoofing.

  • CVE-2004-1950

    Web product uses the IP address in the X-Forwarded-For HTTP header instead of a server variable that uses the connecting IP address, allowing filter bypass.

  • CVE-2001-0908

    Product logs IP address specified by the client instead of obtaining it from the packet headers, allowing information hiding.

  • CVE-2006-1126

    PHP application uses IP address from X-Forwarded-For HTTP header, instead of REMOTE_ADDR.

How attackers exploit it

Step-by-step attacker path

  1. 1

    This code attempts to limit the access of a page to certain IP Addresses. It checks the 'HTTP_X_FORWARDED_FOR' header in case an authorized user is sending the request through a proxy.

  2. 2

    The 'HTTP_X_FORWARDED_FOR' header can be user controlled and so should never be trusted. An attacker can falsify the header to gain access to the page.

  3. 3

    This fixed code only trusts the 'REMOTE_ADDR' header and so avoids the issue:

  4. 4

    Be aware that 'REMOTE_ADDR' can still be spoofed. This may seem useless because the server will send the response to the fake address and not the attacker, but this may still be enough to conduct an attack. For example, if the generatePage() function in this code is resource intensive, an attacker could flood the server with fake requests using an authorized IP and consume significant resources. This could be a serious DoS attack even though the attacker would never see the page's sensitive content.

Vulnerable code example

Vulnerable PHP

This code attempts to limit the access of a page to certain IP Addresses. It checks the 'HTTP_X_FORWARDED_FOR' header in case an authorized user is sending the request through a proxy.

Vulnerable PHP 
$requestingIP = '0.0.0.0';
  if (array_key_exists('HTTP_X_FORWARDED_FOR', $_SERVER)) {
  	$requestingIP = $_SERVER['HTTP_X_FORWARDED_FOR'];
  else{
  	$requestingIP = $_SERVER['REMOTE_ADDR'];
  }
  if(in_array($requestingIP,$ipAllowlist)){
  	generatePage();
  	return;
  }
  else{
  	echo "You are not authorized to view this page";
  	return;
  }
Secure code example

Secure PHP

This fixed code only trusts the 'REMOTE_ADDR' header and so avoids the issue:

Secure PHP 
$requestingIP = '0.0.0.0';
  if (array_key_exists('HTTP_X_FORWARDED_FOR', $_SERVER)) {
  	echo "This application cannot be accessed through a proxy.";
  	return;
  else{
  	$requestingIP = $_SERVER['REMOTE_ADDR'];
  }
```
...*
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-348

  • 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-348

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-348 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-348?

This vulnerability occurs when a system has access to multiple sources for the same critical data, but it chooses to rely on the less secure or less trustworthy one. This creates a security gap because the system ignores better-protected alternatives that offer stronger verification or are harder for attackers to compromise.

How serious is CWE-348?

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-348?

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

How can I prevent CWE-348?

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-348?

Plexicus's SAST engine matches the data-flow signature for CWE-348 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-348?

MITRE publishes the canonical definition at https://cwe.mitre.org/data/definitions/348.html. You can also reference OWASP and NIST documentation for adjacent guidance.

Related weaknesses

Weaknesses related to CWE-348

CWE-345 Parent

Insufficient Verification of Data Authenticity

This vulnerability occurs when an application fails to properly check where data comes from or confirm its legitimacy, allowing untrusted…

CWE-1293 Sibling

Missing Source Correlation of Multiple Independent Data

This vulnerability occurs when a system trusts a single source of data without verification, making it impossible to detect if that source…

CWE-346 Sibling

Origin Validation Error

This vulnerability occurs when an application fails to properly confirm the true origin of incoming data or communication, allowing…

CWE-347 Sibling

Improper Verification of Cryptographic Signature

This vulnerability occurs when an application fails to properly check the digital signature on data, or skips the verification step…

CWE-349 Sibling

Acceptance of Extraneous Untrusted Data With Trusted Data

This vulnerability occurs when a system processes both trusted and untrusted data together, but fails to separate them. The application…

CWE-351 Sibling

Insufficient Type Distinction

This vulnerability occurs when an application fails to properly differentiate between different types of data or objects, leading to…

CWE-352 Sibling

Cross-Site Request Forgery (CSRF)

Cross-Site Request Forgery (CSRF) happens when a web application cannot reliably tell if a user actually intended to submit a request,…

CWE-353 Sibling

Missing Support for Integrity Check

This vulnerability occurs when a system uses a communication protocol that lacks built-in integrity verification, such as a checksum or…

CWE-354 Sibling

Improper Validation of Integrity Check Value

This vulnerability occurs when software fails to properly check the integrity of data by validating its checksum or hash value. Without…

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