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 Incomplete
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…
Definition
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.
Auswirkungen in der Praxis
Real-world CVEs caused by CWE-639
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An educational application does not appropriately restrict file IDs to a particular user. The attacker can brute-force guess IDs, indicating IDOR.
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 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();
... 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-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.
Erkennungssignale
How to detect CWE-639
CWE-639
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.
Häufig gestellte Fragen Was ist CWE-639?
Wie gravierend ist CWE-639?
Welche Sprachen oder Plattformen sind von CWE-639 betroffen?
Wie kann ich CWE-639 verhindern?
Wie erkennt und behebt Plexicus CWE-639?
Wo erfahre ich mehr über CWE-639?
Frequently asked questions
Was ist 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.
Wie gravierend ist CWE-639?
MITRE stuft die Exploit-Wahrscheinlichkeit als hoch ein — diese Schwachstelle wird aktiv in freier Wildbahn ausgenutzt und sollte priorisiert behoben werden.
Welche Sprachen oder Plattformen sind von CWE-639 betroffen?
MITRE hat für diese CWE keine betroffenen Plattformen spezifiziert — sie kann in den meisten Anwendungs-Stacks auftreten.
Wie kann ich CWE-639 verhindern?
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.
Wie erkennt und behebt Plexicus CWE-639?
Die SAST-Engine von Plexicus erkennt die Datenfluss-Signatur von CWE-639 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-639?
MITRE veröffentlicht die kanonische Definition unter https://cwe.mitre.org/data/definitions/639.html. Für ergänzende Hinweise kannst du auch die OWASP- und NIST-Dokumentation heranziehen.
Verwandte Schwachstellen
Weaknesses related to CWE-639
CWE-863 Parent
Incorrect Authorization
This vulnerability occurs when an application checks if a user is allowed to perform an action or access data, but the check is flawed or…
CWE-1244 Sibling
Internal Asset Exposed to Unsafe Debug Access Level or State
This vulnerability occurs when a system's debug or test interface supports multiple access levels, but an internal asset is incorrectly…
CWE-551 Sibling
Incorrect Behavior Order: Authorization Before Parsing and Canonicalization
This vulnerability occurs when a web server checks access permissions before fully processing and normalizing a URL, potentially allowing…
CWE-647 Sibling
Use of Non-Canonical URL Paths for Authorization Decisions
This vulnerability occurs when an application's authorization logic relies on specific URL paths but fails to enforce a single,…
CWE-804 Sibling
Guessable CAPTCHA
This vulnerability occurs when a CAPTCHA challenge is too easy for automated bots to solve, either by guessing or using pattern…
CWE-942 Sibling
Permissive Cross-domain Security Policy with Untrusted Domains
This vulnerability occurs when a web application's cross-domain security policy, like a Content Security Policy (CSP), explicitly allows…
CWE-566 Child
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…
Ressourcen
Further reading
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