CWE-422 Variant Draft

Unprotected Windows Messaging Channel ('Shatter')

This vulnerability, often called a 'Shatter' attack, occurs when a Windows application running with high privileges accepts messages from the Windows messaging system without verifying their source.…

Definition

What is CWE-422?

This vulnerability, often called a 'Shatter' attack, occurs when a Windows application running with high privileges accepts messages from the Windows messaging system without verifying their source. This allows a less-privileged or malicious application to send commands directly to the privileged application, potentially hijacking its functionality.
At its core, this flaw exploits the trust that elevated Windows applications place in the standard messaging system (like SendMessage or PostMessage). Since these messages are not authenticated, any program—including one run by a standard user—can craft and send requests. If the privileged application doesn't check which process sent the message, it will execute the command with its own high-level permissions, letting a low-privilege attacker perform actions they shouldn't be allowed to do. To prevent this, developers must treat incoming Windows messages from untrusted sources with the same suspicion as network data. Implement strict message validation by checking the sender's process ID or using secure communication channels for sensitive operations. Relying solely on User Interface Privilege Isolation (UIPI) on modern systems is not enough; the application's own logic must actively guard its message-handling routines to block unauthorized cross-process communication.
Real-world impact

Real-world CVEs caused by CWE-422

  • CVE-2002-0971

    Bypass GUI and access restricted dialog box.

  • CVE-2002-1230

    Gain privileges via Windows message.

  • CVE-2003-0350

    A control allows a change to a pointer for a callback function using Windows message.

  • CVE-2003-0908

    Product launches Help functionality while running with raised privileges, allowing command execution using Windows message to access "open file" dialog.

  • CVE-2004-0213

    Attacker uses Shatter attack to bypass GUI-enforced protection for CVE-2003-0908.

  • CVE-2004-0207

    User can call certain API functions to modify certain properties of privileged programs.

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-422

  • Architecture and Design Always verify and authenticate the source of the message.
Detection signals

How to detect CWE-422

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-422 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-422?

This vulnerability, often called a 'Shatter' attack, occurs when a Windows application running with high privileges accepts messages from the Windows messaging system without verifying their source. This allows a less-privileged or malicious application to send commands directly to the privileged application, potentially hijacking its functionality.

How serious is CWE-422?

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-422?

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

How can I prevent CWE-422?

Always verify and authenticate the source of the message.

How does Plexicus detect and fix CWE-422?

Plexicus's SAST engine matches the data-flow signature for CWE-422 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-422?

MITRE publishes the canonical definition at https://cwe.mitre.org/data/definitions/422.html. You can also reference OWASP and NIST documentation for adjacent guidance.

Related weaknesses

Weaknesses related to CWE-422

CWE-420 Parent

Unprotected Alternate Channel

This vulnerability occurs when an application secures its main communication path but leaves a backup or alternative channel with weaker…

CWE-1299 Sibling

Missing Protection Mechanism for Alternate Hardware Interface

This vulnerability occurs when a hardware component's security controls only protect the primary access path, leaving alternate interfaces…

CWE-421 Sibling

Race Condition During Access to Alternate Channel

A race condition occurs when an application opens a secondary communication channel intended for an authorized user, but fails to secure…

Resources

Further reading

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