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CWE-179 Base Incomplet
Incorrect Behavior Order: Early Validation
This vulnerability occurs when an application validates user input before applying security filters or data normalization. Attackers can exploit this order of operations by submitting specially…
Définition
What is CWE-179?
This vulnerability occurs when an application validates user input before applying security filters or data normalization. Attackers can exploit this order of operations by submitting specially crafted input that passes the initial validation but becomes malicious after the application's filters or canonicalization processes modify it.
To prevent this flaw, validation logic must always run after data normalization and cleansing steps. Common operations like URL decoding, removing whitespace, or converting character encodings can change the input's structure. If you check for threats before these transformations, you create a window where a harmless-looking payload can be altered into a dangerous command, SQL injection, or path traversal attack after it's already been approved.
Think of it as checking a guest's ID before they take off a disguise. The secure approach is to first standardize the input (e.g., decode all entities, resolve paths), then cleanse it, and finally validate the sanitized result against your security rules. This ensures you are evaluating the actual data that will be used by your application's core logic, closing the bypass opportunity.
Impact réel
Real-world CVEs caused by CWE-179
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Product allows remote attackers to view restricted files via an HTTP request containing a "*" (wildcard or asterisk) character.
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Product modifies the first two letters of a filename extension after performing a security check, which allows remote attackers to bypass authentication via a filename with a .ats extension instead of a .hts extension.
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Database consumes an extra character when processing a character that cannot be converted, which could remove an escape character from the query and make the application subject to SQL injection attacks.
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Overlaps "fakechild/../realchild"
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Product checks URI for "<" and other literal characters, but does it before hex decoding the URI, so "%3E" and other sequences are allowed.
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Directory traversal vulnerability allows remote attackers to read or modify arbitrary files via invalid characters between two . (dot) characters, which are filtered and result in a ".." sequence.
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Directory traversal vulnerability allows attackers to overwrite arbitrary files via invalid characters between two . (dot) characters, which are filtered and result in a ".." sequence.
Comment les attaquants l'exploitent
Parcours de l'attaquant étape par étape
- 1
The following code attempts to validate a given input path by checking it against an allowlist and then return the canonical path. In this specific case, the path is considered valid if it starts with the string "/safe_dir/".
- 2
The problem with the above code is that the validation step occurs before canonicalization occurs. An attacker could provide an input path of "/safe_dir/../" that would pass the validation step. However, the canonicalization process sees the double dot as a traversal to the parent directory and hence when canonicized the path would become just "/".
- 3
To avoid this problem, validation should occur after canonicalization takes place. In this case canonicalization occurs during the initialization of the File object. The code below fixes the issue.
- 4
This script creates a subdirectory within a user directory and sets the user as the owner.
- 5
While the script attempts to screen for '..' sequences, an attacker can submit a directory path including ".~.", which will then become ".." after the filtering step. This allows a Path Traversal (CWE-21) attack to occur.
Exemple de code vulnérable
Vulnerable Java
The following code attempts to validate a given input path by checking it against an allowlist and then return the canonical path. In this specific case, the path is considered valid if it starts with the string "/safe_dir/".
String path = getInputPath();
if (path.startsWith("/safe_dir/"))
{
File f = new File(path);
return f.getCanonicalPath();
} Exemple de code sécurisé
Secure Java
To avoid this problem, validation should occur after canonicalization takes place. In this case canonicalization occurs during the initialization of the File object. The code below fixes the issue.
String path = getInputPath();
File f = new File(path);
if (f.getCanonicalPath().startsWith("/safe_dir/"))
{
return f.getCanonicalPath();
} 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-179
- Implementation Inputs should be decoded and canonicalized to the application's current internal representation before being validated (CWE-180). Make sure that the application does not decode the same input twice (CWE-174). Such errors could be used to bypass allowlist validation schemes by introducing dangerous inputs after they have been checked.
Signaux de détection
How to detect CWE-179
Exécuter des tests de sécurité applicative dynamique (DAST) contre le point de terminaison en ligne.
Surveiller les journaux runtime pour détecter des traces d'exception inhabituelles, des entrées malformées ou des tentatives de contournement d'autorisation.
Revue de code : signaler tout nouveau code qui traite les entrées de cette surface sans utiliser les helpers du framework validés.
Plexicus détecte automatiquement CWE-179 et ouvre une PR de correction en moins de 60 secondes.
Codex Remedium analyse chaque commit, identifie cette faiblesse précise et livre une pull request prête à être relue avec le correctif. Pas de tickets. Pas de transferts.
Questions fréquentes Qu'est-ce que CWE-179 ?
Quelle est la gravité de CWE-179 ?
Quels langages ou plateformes sont affectés par CWE-179 ?
Comment puis-je prévenir CWE-179 ?
Comment Plexicus détecte et corrige CWE-179 ?
Où puis-je en savoir plus sur CWE-179 ?
Frequently asked questions
Qu'est-ce que CWE-179 ?
This vulnerability occurs when an application validates user input before applying security filters or data normalization. Attackers can exploit this order of operations by submitting specially crafted input that passes the initial validation but becomes malicious after the application's filters or canonicalization processes modify it.
Quelle est la gravité de CWE-179 ?
MITRE n'a pas publié de note de probabilité d'exploitation pour cette faiblesse. Traitez-la comme un impact moyen jusqu'à ce que votre modèle de menace prouve le contraire.
Quels langages ou plateformes sont affectés par CWE-179 ?
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-179 ?
Inputs should be decoded and canonicalized to the application's current internal representation before being validated (CWE-180). Make sure that the application does not decode the same input twice (CWE-174). Such errors could be used to bypass allowlist validation schemes by introducing dangerous inputs after they have been checked.
Comment Plexicus détecte et corrige CWE-179 ?
Le moteur SAST de Plexicus reconnaît la signature de flux de données de CWE-179 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-179 ?
MITRE publie la définition canonique à https://cwe.mitre.org/data/definitions/179.html. Vous pouvez également consulter la documentation OWASP et NIST pour des conseils adjacents.
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