Exécuter une analyse statique (SAST) sur le code source à la recherche du motif non sécurisé dans le flux de données.
CWE-176 Variante Brouillon
Improper Handling of Unicode Encoding
This vulnerability occurs when software fails to correctly process or interpret Unicode-encoded input, leading to security bypasses, data corruption, or unexpected behavior.
Définition
What is CWE-176?
This vulnerability occurs when software fails to correctly process or interpret Unicode-encoded input, leading to security bypasses, data corruption, or unexpected behavior.
Unicode allows characters from many languages to be represented, but this complexity can confuse security checks. For example, an application might filter dangerous characters like '../' in ASCII but miss equivalent Unicode representations, allowing attackers to bypass path traversal defenses. Similarly, visual lookalike characters (homoglyphs) can be used in phishing or to impersonate trusted data.
To prevent this, developers must normalize and validate all Unicode input consistently. Use established libraries for canonicalization to ensure characters are compared in their standard form, and apply security checks after normalization—not before. Always treat input handling and comparison logic as encoding-aware, never assuming text is only in basic ASCII.
Impact réel
Real-world CVEs caused by CWE-176
-
Server allows remote attackers to read documents outside of the web root, and possibly execute arbitrary commands, via malformed URLs that contain Unicode encoded characters.
-
Server allows a remote attacker to obtain source code of ASP files via a URL encoded with Unicode.
-
Overlaps interaction error.
Comment les attaquants l'exploitent
Parcours de l'attaquant étape par étape
- 1
Windows provides the MultiByteToWideChar(), WideCharToMultiByte(), UnicodeToBytes(), and BytesToUnicode() functions to convert between arbitrary multibyte (usually ANSI) character strings and Unicode (wide character) strings. The size arguments to these functions are specified in different units, (one in bytes, the other in characters) making their use prone to error.
- 2
In a multibyte character string, each character occupies a varying number of bytes, and therefore the size of such strings is most easily specified as a total number of bytes. In Unicode, however, characters are always a fixed size, and string lengths are typically given by the number of characters they contain. Mistakenly specifying the wrong units in a size argument can lead to a buffer overflow.
- 3
The following function takes a username specified as a multibyte string and a pointer to a structure for user information and populates the structure with information about the specified user. Since Windows authentication uses Unicode for usernames, the username argument is first converted from a multibyte string to a Unicode string.
- 4
This function incorrectly passes the size of unicodeUser in bytes instead of characters. The call to MultiByteToWideChar() can therefore write up to (UNLEN+1)*sizeof(WCHAR) wide characters, or (UNLEN+1)*sizeof(WCHAR)*sizeof(WCHAR) bytes, to the unicodeUser array, which has only (UNLEN+1)*sizeof(WCHAR) bytes allocated.
- 5
If the username string contains more than UNLEN characters, the call to MultiByteToWideChar() will overflow the buffer unicodeUser.
Exemple de code vulnérable
Vulnerable C
The following function takes a username specified as a multibyte string and a pointer to a structure for user information and populates the structure with information about the specified user. Since Windows authentication uses Unicode for usernames, the username argument is first converted from a multibyte string to a Unicode string.
void getUserInfo(char *username, struct _USER_INFO_2 info){
WCHAR unicodeUser[UNLEN+1];
MultiByteToWideChar(CP_ACP, 0, username, -1, unicodeUser, sizeof(unicodeUser));
NetUserGetInfo(NULL, unicodeUser, 2, (LPBYTE *)&info);
} 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-176
- Architecture and Design Avoid making decisions based on names of resources (e.g. files) if those resources can have alternate names.
- Implementation Assume all input is malicious. Use an "accept known good" input validation strategy, i.e., use a list of acceptable inputs that strictly conform to specifications. Reject any input that does not strictly conform to specifications, or transform it into something that does. When performing input validation, consider all potentially relevant properties, including length, type of input, the full range of acceptable values, missing or extra inputs, syntax, consistency across related fields, and conformance to business rules. As an example of business rule logic, "boat" may be syntactically valid because it only contains alphanumeric characters, but it is not valid if the input is only expected to contain colors such as "red" or "blue." Do not rely exclusively on looking for malicious or malformed inputs. This is likely to miss at least one undesirable input, especially if the code's environment changes. This can give attackers enough room to bypass the intended validation. However, denylists can be useful for detecting potential attacks or determining which inputs are so malformed that they should be rejected outright.
- 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-176
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-176 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-176 ?
Quelle est la gravité de CWE-176 ?
Quels langages ou plateformes sont affectés par CWE-176 ?
Comment puis-je prévenir CWE-176 ?
Comment Plexicus détecte et corrige CWE-176 ?
Où puis-je en savoir plus sur CWE-176 ?
Frequently asked questions
Qu'est-ce que CWE-176 ?
This vulnerability occurs when software fails to correctly process or interpret Unicode-encoded input, leading to security bypasses, data corruption, or unexpected behavior.
Quelle est la gravité de CWE-176 ?
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-176 ?
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-176 ?
Avoid making decisions based on names of resources (e.g. files) if those resources can have alternate names. Assume all input is malicious. Use an "accept known good" input validation strategy, i.e., use a list of acceptable inputs that strictly conform to specifications. Reject any input that does not strictly conform to specifications, or transform it into something that does. When performing input validation, consider all potentially relevant properties, including length, type of input, the…
Comment Plexicus détecte et corrige CWE-176 ?
Le moteur SAST de Plexicus reconnaît la signature de flux de données de CWE-176 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-176 ?
MITRE publie la définition canonique à https://cwe.mitre.org/data/definitions/176.html. Vous pouvez également consulter la documentation OWASP et NIST pour des conseils adjacents.
Faiblesses associées
Weaknesses related to CWE-176
CWE-172 Parent
Encoding Error
This vulnerability occurs when software incorrectly transforms data between different formats, leading to corrupted or misinterpreted…
CWE-173 Frère
Improper Handling of Alternate Encoding
This vulnerability occurs when software fails to correctly process input that arrives in a different character encoding than expected,…
CWE-174 Frère
Double Decoding of the Same Data
This vulnerability occurs when an application decodes the same piece of data twice in sequence. This double processing can bypass or…
CWE-175 Frère
Improper Handling of Mixed Encoding
This vulnerability occurs when software fails to correctly process input that contains multiple character encodings within the same data…
CWE-177 Frère
Improper Handling of URL Encoding (Hex Encoding)
This vulnerability occurs when an application fails to correctly process URL-encoded (also known as percent-encoded or hex-encoded) input,…
Prêt quand vous l'êtes
Arrêtez de payer par développeur.
Commencez à fermer la boucle.
Plexicus est l'ASPM natif IA qui scanne, filtre, corrige, penteste et explique — de façon autonome. Développeurs illimités, dépôts illimités, actions IA à usage équitable. Vrai niveau gratuit, €269/mo annuel quand vous êtes prêt.