CWE-831 Variant Incomplete

Signal Handler Function Associated with Multiple Signals

This vulnerability occurs when a single function is registered to handle multiple different operating system signals, creating potential race conditions if that function isn't carefully designed.

Definition

What is CWE-831?

This vulnerability occurs when a single function is registered to handle multiple different operating system signals, creating potential race conditions if that function isn't carefully designed.
When the same function handles multiple signals, an attacker can exploit timing issues by sending a second signal while the handler is still processing the first. If the handler uses shared resources like global variables or non-reentrant functions, this interruption can corrupt program state, potentially leading to crashes, denial of service, or even code execution. Even without classic race conditions, this pattern creates risk. Attackers can trigger the handler multiple times by sending different signals sequentially, causing unintended side effects. This is especially dangerous for handlers designed to run only once, as forced re-execution can bypass security controls or destabilize the application.
Auswirkungen in der Praxis

Real-world CVEs caused by CWE-831

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

Wie Angreifer es ausnutzen

Angreiferpfad Schritt für Schritt

  1. 1

    This code registers the same signal handler function with two different signals.

  2. 2

    This code registers the same signal handler function with two different signals (CWE-831). If those signals are sent to the process, the handler creates a log message (specified in the first argument to the program) and exits.

  3. 3

    The handler function uses global state (globalVar and logMessage), and it can be called by both the SIGHUP and SIGTERM signals. An attack scenario might follow these lines:

  4. 4

    - The program begins execution, initializes logMessage, and registers the signal handlers for SIGHUP and SIGTERM. - The program begins its "normal" functionality, which is simplified as sleep(), but could be any functionality that consumes some time. - The attacker sends SIGHUP, which invokes handler (call this "SIGHUP-handler"). - SIGHUP-handler begins to execute, calling syslog(). - syslog() calls malloc(), which is non-reentrant. malloc() begins to modify metadata to manage the heap. - The attacker then sends SIGTERM. - SIGHUP-handler is interrupted, but syslog's malloc call is still executing and has not finished modifying its metadata. - The SIGTERM handler is invoked. - SIGTERM-handler records the log message using syslog(), then frees the logMessage variable.

  5. 5

    At this point, the state of the heap is uncertain, because malloc is still modifying the metadata for the heap; the metadata might be in an inconsistent state. The SIGTERM-handler call to free() is assuming that the metadata is inconsistent, possibly causing it to write data to the wrong location while managing the heap. The result is memory corruption, which could lead to a crash or even code execution, depending on the circumstances under which the code is running.

Verwundbares Codebeispiel

Vulnerable C

This code registers the same signal handler function with two different signals.

Verwundbar C 
void handler (int sigNum) {
  	...
  }
  int main (int argc, char* argv[]) {
  	signal(SIGUSR1, handler)
  	signal(SIGUSR2, handler)
  }
Sicheres Codebeispiel

Secure pseudo

Sicher 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-831

  • 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-831

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-831 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-831?

This vulnerability occurs when a single function is registered to handle multiple different operating system signals, creating potential race conditions if that function isn't carefully designed.

Wie gravierend ist CWE-831?

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-831 betroffen?

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

Wie kann ich CWE-831 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-831?

Die SAST-Engine von Plexicus erkennt die Datenfluss-Signatur von CWE-831 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-831?

MITRE veröffentlicht die kanonische Definition unter https://cwe.mitre.org/data/definitions/831.html. Für ergänzende Hinweise kannst du auch die OWASP- und NIST-Dokumentation heranziehen.

Verwandte Schwachstellen

Weaknesses related to CWE-831

CWE-364 Parent

Signal Handler Race Condition

A signal handler race condition occurs when a program's signal handling routine is vulnerable to timing issues, allowing its state to be…

CWE-432 Sibling

Dangerous Signal Handler not Disabled During Sensitive Operations

This vulnerability occurs when a program's signal handler, which shares resources like global variables with other handlers, can be…

CWE-828 Sibling

Signal Handler with Functionality that is not Asynchronous-Safe

This weakness occurs when a program's signal handler contains code that is not asynchronous-safe. This means the handler can be…

Ressourcen

Further reading

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