CWE-507 Base Incomplete

Trojan Horse

A Trojan Horse vulnerability occurs when software presents itself as legitimate and useful, but secretly contains malicious functionality that bypasses security controls. This hidden code operates…

Definition

What is CWE-507?

A Trojan Horse vulnerability occurs when software presents itself as legitimate and useful, but secretly contains malicious functionality that bypasses security controls. This hidden code operates without the user's knowledge, violating the intended security policy of the system or its administrator.
This vulnerability exploits the trust relationship between users and software. Developers and users expect an application to perform only its advertised functions, but a Trojan Horse embeds additional, harmful actions within that trusted package. These hidden features might steal data, create backdoors, damage systems, or provide unauthorized access, all while the visible interface appears completely normal and benign. From a development perspective, this often stems from incorporating third-party components, libraries, or plugins without rigorous security review. It can also occur in supply chain attacks where build processes are compromised. To mitigate this risk, enforce strict code provenance controls, use software composition analysis tools to audit dependencies, and implement code signing with verification to ensure integrity from development through deployment.
Real-world impact

Real-world CVEs caused by CWE-507

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-507

  • Operation Most antivirus software scans for Trojan Horses.
  • Installation Verify the integrity of the product that is being installed.
Detection signals

How to detect CWE-507

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-507 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-507?

A Trojan Horse vulnerability occurs when software presents itself as legitimate and useful, but secretly contains malicious functionality that bypasses security controls. This hidden code operates without the user's knowledge, violating the intended security policy of the system or its administrator.

How serious is CWE-507?

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-507?

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

How can I prevent CWE-507?

Most antivirus software scans for Trojan Horses. Verify the integrity of the product that is being installed.

How does Plexicus detect and fix CWE-507?

Plexicus's SAST engine matches the data-flow signature for CWE-507 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-507?

MITRE publishes the canonical definition at https://cwe.mitre.org/data/definitions/507.html. You can also reference OWASP and NIST documentation for adjacent guidance.

Related weaknesses

Weaknesses related to CWE-507

CWE-506 Parent

Embedded Malicious Code

This vulnerability occurs when an application or codebase contains intentionally harmful code inserted by a developer or third party.

CWE-510 Sibling

Trapdoor

A trapdoor, often called a backdoor, is a hidden piece of code intentionally placed within software. It activates in response to a…

CWE-511 Sibling

Logic/Time Bomb

A logic or time bomb is malicious code intentionally placed within software to trigger harmful actions when a specific condition is met or…

CWE-512 Sibling

Spyware

Spyware is software that secretly gathers personal information about a user or their activities. It does this by accessing data from other…

CWE-508 Child

Non-Replicating Malicious Code

This type of malicious code is designed to operate only on the specific system it initially infects. Unlike viruses or worms, it does not…

CWE-509 Child

Replicating Malicious Code (Virus or Worm)

This weakness describes software that is vulnerable to infection by self-replicating malicious programs like viruses or worms. Once such…

Resources

Further reading

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