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-639 Base Incomplet
Authorization Bypass Through User-Controlled Key
This vulnerability occurs when an application's authorization system fails to verify that a user is allowed to access specific data before retrieving it, allowing an attacker to access another…
Définition
What is CWE-639?
This vulnerability occurs when an application's authorization system fails to verify that a user is allowed to access specific data before retrieving it, allowing an attacker to access another user's information by manipulating an identifier they control.
This flaw typically appears in features that fetch user-specific data, like account pages or search results. The application uses a key—such as a database ID, account number, or session token—to locate the correct record. However, if this key is taken directly from a user-controllable source like a URL parameter, form field, or cookie without verifying the requesting user's permissions, an attacker can simply change the key value to access data belonging to someone else.
Attackers often exploit this by tampering with sequential, predictable, or easily-guessed identifiers. For instance, using a simple integer like `user_id=1001` and changing it to `1002` to access another account. The core failure is that the system performs a lookup based on the provided key but skips the critical authorization check to confirm the authenticated user actually owns or has the right to view that specific record.
Impact réel
Real-world CVEs caused by CWE-639
-
An educational application does not appropriately restrict file IDs to a particular user. The attacker can brute-force guess IDs, indicating IDOR.
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#
The following code uses a parameterized statement, which escapes metacharacters and prevents SQL injection vulnerabilities, to construct and execute a SQL query that searches for an invoice matching the specified identifier [1]. The identifier is selected from a list of all invoices associated with the current authenticated user.
...
conn = new SqlConnection(_ConnectionString);
conn.Open();
int16 id = System.Convert.ToInt16(invoiceID.Text);
SqlCommand query = new SqlCommand( "SELECT * FROM invoices WHERE id = @id", conn);
query.Parameters.AddWithValue("@id", id);
SqlDataReader objReader = objCommand.ExecuteReader();
... 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-639
- Architecture and Design For each and every data access, ensure that the user has sufficient privilege to access the record that is being requested.
- Architecture and Design / Implementation Make sure that the key that is used in the lookup of a specific user's record is not controllable externally by the user or that any tampering can be detected.
- Architecture and Design Use encryption in order to make it more difficult to guess other legitimate values of the key or associate a digital signature with the key so that the server can verify that there has been no tampering.
Signaux de détection
How to detect CWE-639
CWE-639
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Questions fréquentes Qu'est-ce que CWE-639 ?
Quelle est la gravité de CWE-639 ?
Quels langages ou plateformes sont affectés par CWE-639 ?
Comment puis-je prévenir CWE-639 ?
Comment Plexicus détecte et corrige CWE-639 ?
Où puis-je en savoir plus sur CWE-639 ?
Frequently asked questions
Qu'est-ce que CWE-639 ?
This vulnerability occurs when an application's authorization system fails to verify that a user is allowed to access specific data before retrieving it, allowing an attacker to access another user's information by manipulating an identifier they control.
Quelle est la gravité de CWE-639 ?
MITRE évalue la probabilité d'exploitation comme Élevée — cette faiblesse est activement exploitée et doit être priorisée pour la remédiation.
Quels langages ou plateformes sont affectés par CWE-639 ?
MITRE n'a pas spécifié les plateformes affectées pour ce CWE — il peut s'appliquer à la plupart des stacks applicatives.
Comment puis-je prévenir CWE-639 ?
For each and every data access, ensure that the user has sufficient privilege to access the record that is being requested. Make sure that the key that is used in the lookup of a specific user's record is not controllable externally by the user or that any tampering can be detected.
Comment Plexicus détecte et corrige CWE-639 ?
Le moteur SAST de Plexicus reconnaît la signature de flux de données de CWE-639 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-639 ?
MITRE publie la définition canonique à https://cwe.mitre.org/data/definitions/639.html. Vous pouvez également consulter la documentation OWASP et NIST pour des conseils adjacents.
Faiblesses associées
Weaknesses related to CWE-639
CWE-863 Parent
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CWE-804 Frère
Guessable CAPTCHA
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CWE-566 Enfant
Authorization Bypass Through User-Controlled SQL Primary Key
This vulnerability occurs when an application allows a user to directly control the primary key value used in a SQL query, enabling them…
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