Automated static analysis, commonly referred to as Static Application Security Testing (SAST), can find some instances of this weakness by analyzing source code (or binary/compiled code) without having to execute it. Typically, this is done by building a model of data flow and control flow, then searching for potentially-vulnerable patterns that connect "sources" (origins of input) with "sinks" (destinations where the data interacts with external components, a lower layer such as the OS, etc.)
CWE-391 Base Incomplete
Unchecked Error Condition
This vulnerability occurs when a program fails to properly check or handle error conditions, such as exceptions or return codes. By ignoring these failures, the software can enter an unexpected…
Definition
What is CWE-391?
This vulnerability occurs when a program fails to properly check or handle error conditions, such as exceptions or return codes. By ignoring these failures, the software can enter an unexpected state that attackers might exploit, often without any logging or user notification.
When your code doesn't check for errors—like a failed file operation, a null pointer, or a network timeout—it continues executing as if nothing went wrong. This creates a gap between what the program assumes is true (e.g., 'the data was loaded') and reality (e.g., 'the variable is empty'), leading to crashes, data corruption, or security bypasses. Attackers can deliberately trigger these ignored errors to destabilize your application or reveal sensitive information.
To prevent this, always implement robust error handling. Check return values from functions, use try-catch blocks for exceptions, and validate system call outcomes. Log all caught errors with sufficient context for debugging, and decide on safe failure modes—like rolling back transactions or terminating the session—instead of silently proceeding. This defensive practice closes a common attack vector and makes your software more resilient and observable in production.
Auswirkungen in der Praxis
Real-world CVEs caused by CWE-391
Bisher sind in MITREs Katalog keine öffentlichen CVE-Referenzen mit dieser CWE verknüpft.
Wie Angreifer es ausnutzen
Angreiferpfad Schritt für Schritt
- 1
Identifiziere einen Codepfad, der nicht vertrauenswürdige Eingaben ohne Validierung verarbeitet.
- 2
Erzeuge eine Payload, die das unsichere Verhalten auslöst — Injection, Traversal, Overflow oder Logik-Missbrauch.
- 3
Liefere die Payload über einen normalen Request aus und beobachte die Reaktion der Anwendung.
- 4
Iteriere, bis die Antwort Daten preisgibt, Angreifer-Code ausführt oder Berechtigungen eskaliert.
Verwundbares Codebeispiel
Vulnerable Java
The following code excerpt ignores a rarely-thrown exception from doExchange().
try {
doExchange();
}
catch (RareException e) {
```
// this can never happen*
} Sicheres Codebeispiel
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.
Präventions-Checkliste
How to prevent CWE-391
- Requirements The choice between a language which has named or unnamed exceptions needs to be done. While unnamed exceptions exacerbate the chance of not properly dealing with an exception, named exceptions suffer from the up call version of the weak base class problem.
- Requirements A language can be used which requires, at compile time, to catch all serious exceptions. However, one must make sure to use the most current version of the API as new exceptions could be added.
- Implementation Catch all relevant exceptions. This is the recommended solution. Ensure that all exceptions are handled in such a way that you can be sure of the state of your system at any given moment.
Erkennungssignale
How to detect CWE-391
Plexicus erkennt CWE-391 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.
Häufig gestellte Fragen Was ist CWE-391?
Wie gravierend ist CWE-391?
Welche Sprachen oder Plattformen sind von CWE-391 betroffen?
Wie kann ich CWE-391 verhindern?
Wie erkennt und behebt Plexicus CWE-391?
Wo erfahre ich mehr über CWE-391?
Frequently asked questions
Was ist CWE-391?
This vulnerability occurs when a program fails to properly check or handle error conditions, such as exceptions or return codes. By ignoring these failures, the software can enter an unexpected state that attackers might exploit, often without any logging or user notification.
Wie gravierend ist CWE-391?
MITRE stuft die Exploit-Wahrscheinlichkeit als mittel ein — eine Ausnutzung ist realistisch, erfordert aber meist bestimmte Bedingungen.
Welche Sprachen oder Plattformen sind von CWE-391 betroffen?
MITRE hat für diese CWE keine betroffenen Plattformen spezifiziert — sie kann in den meisten Anwendungs-Stacks auftreten.
Wie kann ich CWE-391 verhindern?
The choice between a language which has named or unnamed exceptions needs to be done. While unnamed exceptions exacerbate the chance of not properly dealing with an exception, named exceptions suffer from the up call version of the weak base class problem. A language can be used which requires, at compile time, to catch all serious exceptions. However, one must make sure to use the most current version of the API as new exceptions could be added.
Wie erkennt und behebt Plexicus CWE-391?
Die SAST-Engine von Plexicus erkennt die Datenfluss-Signatur von CWE-391 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-391?
MITRE veröffentlicht die kanonische Definition unter https://cwe.mitre.org/data/definitions/391.html. Für ergänzende Hinweise kannst du auch die OWASP- und NIST-Dokumentation heranziehen.
Verwandte Schwachstellen
Weaknesses related to CWE-391
CWE-754 Parent
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…
CWE-252 Sibling
Unchecked Return Value
This vulnerability occurs when a program fails to verify the result of a function or method call, allowing it to continue execution…
CWE-253 Sibling
Incorrect Check of Function Return Value
This vulnerability occurs when a program misinterprets or improperly validates the return value from a function, causing it to miss…
CWE-273 Sibling
Improper Check for Dropped Privileges
This vulnerability occurs when an application tries to lower its system privileges but fails to verify that the operation was successful.
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…
CWE-394 Sibling
Unexpected Status Code or Return Value
This vulnerability occurs when software fails to properly validate the full range of possible return values from a function or system…
CWE-476 Sibling
NULL Pointer Dereference
This vulnerability occurs when a program attempts to access or manipulate memory using a pointer that is set to NULL, causing a crash or…
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