CWE-755 Class Incomplete Medium likelihood

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 state.

Definition

What is CWE-755?

This vulnerability occurs when software fails to properly manage unexpected situations or errors, leaving it in an unstable or insecure state.
When a program encounters something unexpected—like a failed network connection, corrupted data, or exhausted system resources—it must handle it gracefully. Improper exception handling means the software might crash, expose sensitive debugging information, or continue operating with incorrect assumptions, creating openings for attackers to exploit. To prevent this, developers should implement robust error handling that anticipates potential failure points. This includes using structured exception handling mechanisms, defining clear recovery procedures, validating all external inputs, and ensuring the application fails securely without leaking internal details that could aid an attacker.
Auswirkungen in der Praxis

Real-world CVEs caused by CWE-755

  • CVE-2023-41151

    SDK for OPC Unified Architecture (OPC UA) server has uncaught exception when a socket is blocked for writing but the server tries to send an error

  • [REF-1374]

    Chain: JavaScript-based cryptocurrency library can fall back to the insecure Math.random() function instead of reporting a failure (CWE-392), thus reducing the entropy (CWE-332) and leading to generation of non-unique cryptographic keys for Bitcoin wallets (CWE-1391)

  • CVE-2021-3011

    virtual interrupt controller in a virtualization product allows crash of host by writing a certain invalid value to a register, which triggers a fatal error instead of returning an error code

  • CVE-2008-4302

    Chain: OS kernel does not properly handle a failure of a function call (CWE-755), leading to an unlock of a resource that was not locked (CWE-832), with resultant crash.

Wie Angreifer es ausnutzen

Angreiferpfad Schritt für Schritt

  1. 1

    The following example attempts to resolve a hostname.

  2. 2

    A DNS lookup failure will cause the Servlet to throw an exception.

  3. 3

    The following example attempts to allocate memory for a character. After the call to malloc, an if statement is used to check whether the malloc function failed.

  4. 4

    The conditional successfully detects a NULL return value from malloc indicating a failure, however it does not do anything to handle the problem. Unhandled errors may have unexpected results and may cause the program to crash or terminate.

  5. 5

    Instead, the if block should contain statements that either attempt to fix the problem or notify the user that an error has occurred and continue processing or perform some cleanup and gracefully terminate the program. The following example notifies the user that the malloc function did not allocate the required memory resources and returns an error code.

Verwundbares Codebeispiel

Vulnerable Java

The following example attempts to resolve a hostname.

Verwundbar Java 
protected void doPost (HttpServletRequest req, HttpServletResponse res) throws IOException {
  	String ip = req.getRemoteAddr();
  	InetAddress addr = InetAddress.getByName(ip);
  	...
  	out.println("hello " + addr.getHostName());
  }
Sicheres Codebeispiel

Secure C

Instead, the if block should contain statements that either attempt to fix the problem or notify the user that an error has occurred and continue processing or perform some cleanup and gracefully terminate the program. The following example notifies the user that the malloc function did not allocate the required memory resources and returns an error code.

Sicher C 
foo=malloc(sizeof(char)); //the next line checks to see if malloc failed
  if (foo==NULL) {
  	printf("Malloc failed to allocate memory resources");
  	return -1;
  }
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-755

  • 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-755

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-755 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-755?

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

Wie gravierend ist CWE-755?

MITRE stuft die Exploit-Wahrscheinlichkeit als mittel ein — eine Ausnutzung ist realistisch, erfordert aber meist bestimmte Bedingungen.

Welche Sprachen oder Plattformen sind von CWE-755 betroffen?

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

Wie kann ich CWE-755 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-755?

Die SAST-Engine von Plexicus erkennt die Datenfluss-Signatur von CWE-755 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-755?

MITRE veröffentlicht die kanonische Definition unter https://cwe.mitre.org/data/definitions/755.html. Für ergänzende Hinweise kannst du auch die OWASP- und NIST-Dokumentation heranziehen.

Verwandte Schwachstellen

Weaknesses related to CWE-755

CWE-703 Parent

Improper Check or Handling of Exceptional Conditions

This vulnerability occurs when software fails to properly plan for or manage rare but possible error scenarios, leaving it unprepared for…

CWE-1384 Sibling

Improper Handling of Physical or Environmental Conditions

This weakness occurs when a hardware device fails to manage unexpected physical or environmental situations, whether they happen naturally…

CWE-228 Sibling

Improper Handling of Syntactically Invalid Structure

This vulnerability occurs when software fails to properly reject or process input that doesn't follow the expected format or structure,…

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-391 Sibling

Unchecked Error Condition

This vulnerability occurs when a program fails to properly check or handle error conditions, such as exceptions or return codes. By…

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-393 Sibling

Return of Wrong Status Code

This vulnerability occurs when a function returns an inaccurate status code or value that misrepresents the actual outcome of an…

CWE-397 Sibling

Declaration of Throws for Generic Exception

This vulnerability occurs when a method is declared to throw an overly broad exception type, such as a generic 'Exception' or 'Throwable'.…

CWE-754 Sibling

Improper Check for Unusual or Exceptional Conditions

This weakness occurs when software fails to properly anticipate and handle rare or unexpected runtime situations that fall outside normal…

Ressourcen

Further reading

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