CWE-756 Base Incomplete

Missing Custom Error Page

This vulnerability occurs when an application fails to display its own user-friendly error pages, instead falling back to default system messages that can leak sensitive technical details.

Definition

What is CWE-756?

This vulnerability occurs when an application fails to display its own user-friendly error pages, instead falling back to default system messages that can leak sensitive technical details.
When an application crashes or encounters an unexpected condition, the web server or framework often generates a default error response. These generic pages can be a goldmine for attackers, revealing stack traces, database schemas, server versions, internal file paths, or snippets of code. This exposed information significantly lowers the effort required for further exploitation, as it provides clear clues about the underlying technology and potential weaknesses. To prevent this, developers should implement a centralized error handler that intercepts all uncaught exceptions and HTTP error statuses (like 404 or 500). This handler must then respond with a consistent, branded page that informs the user a problem occurred—without any technical details—while logging the full diagnostic information securely on the server side for internal debugging. This simple practice improves both security and user experience.
Auswirkungen in der Praxis

Real-world CVEs caused by CWE-756

Bisher sind in MITREs Katalog keine öffentlichen CVE-Referenzen mit dieser CWE verknüpft.

Wie Angreifer es ausnutzen

Angreiferpfad Schritt für Schritt

  1. 1

    In the snippet below, an unchecked runtime exception thrown from within the try block may cause the container to display its default error page (which may contain a full stack trace, among other things).

  2. 2

    The mode attribute of the tag in the Web.config file defines whether custom or default error pages are used.

  3. 3

    In the following insecure ASP.NET application setting, custom error message mode is turned off. An ASP.NET error message with detailed stack trace and platform versions will be returned.

  4. 4

    A more secure setting is to set the custom error message mode for remote users only. No defaultRedirect error page is specified. The local user on the web server will see a detailed stack trace. For remote users, an ASP.NET error message with the server customError configuration setting and the platform version will be returned.

  5. 5

    Another secure option is to set the mode attribute of the tag to use a custom page as follows:

Verwundbares Codebeispiel

Vulnerable Java

In the snippet below, an unchecked runtime exception thrown from within the try block may cause the container to display its default error page (which may contain a full stack trace, among other things).

Verwundbar Java 
Public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
  	try {
  		...
  	} catch (ApplicationSpecificException ase) {
  		logger.error("Caught: " + ase.toString());
  	}
  }
Sicheres Codebeispiel

Secure ASP.NET

A more secure setting is to set the custom error message mode for remote users only. No defaultRedirect error page is specified. The local user on the web server will see a detailed stack trace. For remote users, an ASP.NET error message with the server customError configuration setting and the platform version will be returned.

Sicher ASP.NET 
<customErrors mode="RemoteOnly" />
What changed: the unsafe sink is replaced (or the input is validated/escaped) so the same payload no longer triggers the weakness.
Präventions-Checkliste

How to prevent CWE-756

  • 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.
Erkennungssignale

How to detect CWE-756

SAST High

Führe statische Analyse (SAST) auf der Codebasis aus und suche im Datenfluss nach dem unsicheren Muster.

DAST Moderate

Führe dynamische Application-Security-Tests gegen den Live-Endpoint aus.

Runtime Moderate

Beobachte Runtime-Logs auf ungewöhnliche Exception-Traces, fehlerhafte Eingaben oder Versuche, Autorisierung zu umgehen.

Code review Moderate

Code Review: Markiere jeden neuen Code, der Eingaben von dieser Oberfläche ohne validierte Framework-Helper verarbeitet.

Plexicus Auto-Fix

Plexicus erkennt CWE-756 automatisch und öffnet in unter 60 Sekunden einen Fix-PR.

Codex Remedium scannt jeden Commit, identifiziert genau diese Schwachstelle und liefert einen reviewer-ready Pull Request mit dem Patch. Keine Tickets. Keine Hand-offs.

Demo anfordern Plexicus kostenlos testen
Häufig gestellte Fragen

Frequently asked questions

Was ist CWE-756?

This vulnerability occurs when an application fails to display its own user-friendly error pages, instead falling back to default system messages that can leak sensitive technical details.

Wie gravierend ist CWE-756?

MITRE hat für diese Schwachstelle keine Exploit-Wahrscheinlichkeit veröffentlicht. Behandle sie als mittlere Auswirkung, bis dein Threat Model anderes belegt.

Welche Sprachen oder Plattformen sind von CWE-756 betroffen?

MITRE hat für diese CWE keine betroffenen Plattformen spezifiziert — sie kann in den meisten Anwendungs-Stacks auftreten.

Wie kann ich CWE-756 verhindern?

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.

Wie erkennt und behebt Plexicus CWE-756?

Die SAST-Engine von Plexicus erkennt die Datenfluss-Signatur von CWE-756 bei jedem Commit. Bei einem Treffer öffnet unser Codex-Remedium-Agent einen Fix-PR mit korrigiertem Code, Tests und einer einzeiligen Zusammenfassung für den Reviewer.

Wo erfahre ich mehr über CWE-756?

MITRE veröffentlicht die kanonische Definition unter https://cwe.mitre.org/data/definitions/756.html. Für ergänzende Hinweise kannst du auch die OWASP- und NIST-Dokumentation heranziehen.

Verwandte Schwachstellen

Weaknesses related to CWE-756

CWE-755 Parent

Improper Handling of Exceptional Conditions

This vulnerability occurs when software fails to properly manage unexpected situations or errors, leaving it in an unstable or insecure…

CWE-209 Sibling

Generation of Error Message Containing Sensitive Information

This vulnerability occurs when an application reveals sensitive details about its internal systems, user data, or environment within error…

CWE-248 Sibling

Uncaught Exception

This vulnerability occurs when a function throws an error or exception, but the calling code does not have a proper handler to catch and…

CWE-274 Sibling

Improper Handling of Insufficient Privileges

This vulnerability occurs when an application fails to properly manage situations where it lacks the necessary permissions to execute an…

CWE-280 Sibling

Improper Handling of Insufficient Permissions or Privileges

This vulnerability occurs when a system fails to properly manage situations where it lacks the necessary permissions to perform an action…

CWE-333 Sibling

Improper Handling of Insufficient Entropy in TRNG

This vulnerability occurs when a system fails to properly manage the limited or unpredictable output rate of a true random number…

CWE-390 Sibling

Detection of Error Condition Without Action

This weakness occurs when software successfully identifies an error condition but then fails to take any meaningful action to address it.…

CWE-392 Sibling

Missing Report of Error Condition

This vulnerability occurs when a system fails to properly signal that an error has happened. Instead of returning a clear error code,…

CWE-395 Sibling

Use of NullPointerException Catch to Detect NULL Pointer Dereference

Using a try-catch block for NullPointerException as a substitute for proper null checks is an anti-pattern. This approach masks the root…

Ressourcen

Further reading

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