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-479 Variante Brouillon
Signal Handler Use of a Non-reentrant Function
This vulnerability occurs when a signal handler in your code calls a function that is not safe to re-enter. If that function is interrupted and called again before it finishes, it can corrupt memory…
Définition
What is CWE-479?
This vulnerability occurs when a signal handler in your code calls a function that is not safe to re-enter. If that function is interrupted and called again before it finishes, it can corrupt memory and crash your program or create security weaknesses.
Non-reentrant functions rely on global data or static memory to do their work. When a signal interrupts such a function and the handler calls the same function again, both invocations compete for and corrupt that shared state. Common examples include `malloc()`, `free()`, and `syslog()`, which use internal scratch space or metadata to track operations. This corruption can leave your application in an unpredictable and potentially exploitable state.
As a developer, you must ensure that only async-signal-safe functions are called from within a signal handler. The POSIX standard defines a specific list of these safe functions. Calling anything outside this list, especially standard library functions that manage memory or perform I/O, introduces this risk of re-entrancy corruption which can lead to denial of service or, in worst cases, allow an attacker to execute arbitrary code.
Impact réel
Real-world CVEs caused by CWE-479
-
signal handler calls function that ultimately uses malloc()
-
SIGCHLD signal to FTP server can cause crash under heavy load while executing non-reentrant functions like malloc/free.
Comment les attaquants l'exploitent
Parcours de l'attaquant étape par étape
- 1
Identifier un chemin de code qui traite des entrées non fiables sans validation.
- 2
Élaborer une charge utile qui exploite le comportement non sécurisé — injection, traversal, débordement ou abus de logique.
- 3
Délivrer la charge utile via une requête normale et observer la réaction de l'application.
- 4
Itérer jusqu'à ce que la réponse divulgue des données, exécute le code de l'attaquant ou élève les privilèges.
Exemple de code vulnérable
Vulnerable C
In this example, a signal handler uses syslog() to log a message:
char *message;
void sh(int dummy) {
syslog(LOG_NOTICE,"%s\n",message);
sleep(10);
exit(0);
}
int main(int argc,char* argv[]) {
...
signal(SIGHUP,sh);
signal(SIGTERM,sh);
sleep(10);
exit(0);
}
If the execution of the first call to the signal handler is suspended after invoking syslog(), and the signal handler is called a second time, the memory allocated by syslog() enters an undefined, and possibly, exploitable state. Exemple de code sécurisé
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.
Liste de contrôle de prévention
How to prevent CWE-479
- Requirements Require languages or libraries that provide reentrant functionality, or otherwise make it easier to avoid this weakness.
- Architecture and Design Design signal handlers to only set flags rather than perform complex functionality.
- Implementation Ensure that non-reentrant functions are not found in signal handlers.
- Implementation Use sanity checks to reduce the timing window for exploitation of race conditions. This is only a partial solution, since many attacks might fail, but other attacks still might work within the narrower window, even accidentally.
Signaux de détection
How to detect CWE-479
CWE-479
Don't catalog this weakness. Prove it's reachable.
Plexicus turns CWE catalogs into evidence: every CWE-pattern is matched against your real code graph, reach is proven on a sandbox clone, and verified findings ship as reviewed PRs.
Questions fréquentes Qu'est-ce que CWE-479 ?
Quelle est la gravité de CWE-479 ?
Quels langages ou plateformes sont affectés par CWE-479 ?
Comment puis-je prévenir CWE-479 ?
Comment Plexicus détecte et corrige CWE-479 ?
Où puis-je en savoir plus sur CWE-479 ?
Frequently asked questions
Qu'est-ce que CWE-479 ?
This vulnerability occurs when a signal handler in your code calls a function that is not safe to re-enter. If that function is interrupted and called again before it finishes, it can corrupt memory and crash your program or create security weaknesses.
Quelle est la gravité de CWE-479 ?
MITRE évalue la probabilité d'exploitation comme Faible — l'exploitation est rare, mais la faiblesse doit tout de même être corrigée lorsqu'elle est découverte.
Quels langages ou plateformes sont affectés par CWE-479 ?
MITRE lists the following affected platforms: C, C++.
Comment puis-je prévenir CWE-479 ?
Require languages or libraries that provide reentrant functionality, or otherwise make it easier to avoid this weakness. Design signal handlers to only set flags rather than perform complex functionality.
Comment Plexicus détecte et corrige CWE-479 ?
Le moteur SAST de Plexicus reconnaît la signature de flux de données de CWE-479 à chaque commit. Lorsqu'une correspondance est trouvée, notre agent Codex Remedium ouvre une PR de correction avec le code corrigé, les tests et un résumé d'une ligne pour le relecteur.
Où puis-je en savoir plus sur CWE-479 ?
MITRE publie la définition canonique à https://cwe.mitre.org/data/definitions/479.html. Vous pouvez également consulter la documentation OWASP et NIST pour des conseils adjacents.
Faiblesses associées
Weaknesses related to CWE-479
CWE-828 Parent
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…
CWE-123 Peut précéder
Write-what-where Condition
A write-what-where condition occurs when an attacker can control both the data written and the exact memory location where it's written,…
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