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-86 Variante Brouillon
Improper Neutralization of Invalid Characters in Identifiers in Web Pages
This vulnerability occurs when an application fails to properly filter or escape invalid characters within web identifiers like HTML tag names or URI schemes, allowing malicious sequences to pass…
Définition
What is CWE-86?
This vulnerability occurs when an application fails to properly filter or escape invalid characters within web identifiers like HTML tag names or URI schemes, allowing malicious sequences to pass through.
Modern web browsers often interpret malformed identifiers in unexpected ways. For instance, a browser might silently strip out null bytes or other invalid characters, reconstructing a dangerous payload that the developer's filters missed. This creates a gap where your security checks see a harmless string, but the browser executes it as active code.
Attackers exploit this by embedding these invalid sequences—like null bytes or alternative encodings—within identifiers such as URI schemes. A common bypass involves encoding "javascript:" as something like `java%00script:`, which might bypass a simple blacklist filter but still render as executable JavaScript in the browser, leading to cross-site scripting (XSS) or other client-side attacks.
Impact réel
Real-world CVEs caused by CWE-86
-
XSS filter doesn't filter null characters before looking for dangerous tags, which are ignored by web browsers. Multiple Interpretation Error (MIE) and validate-before-cleanse.
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 pseudo
MITRE n'a pas publié d'exemple de code pour ce CWE. Le motif ci-dessous est illustratif — voir Ressources pour les références canoniques.
// Example pattern — see MITRE for the canonical references.
function handleRequest(input) {
// Untrusted input flows directly into the sensitive sink.
return executeUnsafe(input);
} 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-86
- Implementation Use and specify an output encoding that can be handled by the downstream component that is reading the output. Common encodings include ISO-8859-1, UTF-7, and UTF-8. When an encoding is not specified, a downstream component may choose a different encoding, either by assuming a default encoding or automatically inferring which encoding is being used, which can be erroneous. When the encodings are inconsistent, the downstream component might treat some character or byte sequences as special, even if they are not special in the original encoding. Attackers might then be able to exploit this discrepancy and conduct injection attacks; they even might be able to bypass protection mechanisms that assume the original encoding is also being used by the downstream component. The problem of inconsistent output encodings often arises in web pages. If an encoding is not specified in an HTTP header, web browsers often guess about which encoding is being used. This can open up the browser to subtle XSS attacks.
- Implementation To help mitigate XSS attacks against the user's session cookie, set the session cookie to be HttpOnly. In browsers that support the HttpOnly feature (such as more recent versions of Internet Explorer and Firefox), this attribute can prevent the user's session cookie from being accessible to malicious client-side scripts that use document.cookie. This is not a complete solution, since HttpOnly is not supported by all browsers. More importantly, XMLHTTPRequest and other powerful browser technologies provide read access to HTTP headers, including the Set-Cookie header in which the HttpOnly flag is set.
Signaux de détection
How to detect CWE-86
Plexicus détecte automatiquement CWE-86 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-86 ?
Quelle est la gravité de CWE-86 ?
Quels langages ou plateformes sont affectés par CWE-86 ?
Comment puis-je prévenir CWE-86 ?
Comment Plexicus détecte et corrige CWE-86 ?
Où puis-je en savoir plus sur CWE-86 ?
Frequently asked questions
Qu'est-ce que CWE-86 ?
This vulnerability occurs when an application fails to properly filter or escape invalid characters within web identifiers like HTML tag names or URI schemes, allowing malicious sequences to pass through.
Quelle est la gravité de CWE-86 ?
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-86 ?
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-86 ?
Use and specify an output encoding that can be handled by the downstream component that is reading the output. Common encodings include ISO-8859-1, UTF-7, and UTF-8. When an encoding is not specified, a downstream component may choose a different encoding, either by assuming a default encoding or automatically inferring which encoding is being used, which can be erroneous. When the encodings are inconsistent, the downstream component might treat some character or byte sequences as special,…
Comment Plexicus détecte et corrige CWE-86 ?
Le moteur SAST de Plexicus reconnaît la signature de flux de données de CWE-86 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-86 ?
MITRE publie la définition canonique à https://cwe.mitre.org/data/definitions/86.html. Vous pouvez également consulter la documentation OWASP et NIST pour des conseils adjacents.
Faiblesses associées
Weaknesses related to CWE-86
CWE-79 Parent
Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')
This vulnerability occurs when a web application fails to properly sanitize or encode user-supplied input before displaying it on a…
CWE-80 Frère
Improper Neutralization of Script-Related HTML Tags in a Web Page (Basic XSS)
This vulnerability, commonly known as Basic Cross-Site Scripting (XSS), occurs when a web application fails to properly sanitize user…
CWE-81 Frère
Improper Neutralization of Script in an Error Message Web Page
This vulnerability occurs when an application fails to properly sanitize user-supplied input before displaying it within an error message…
CWE-83 Frère
Improper Neutralization of Script in Attributes in a Web Page
This vulnerability occurs when a web application fails to properly sanitize or block JavaScript URIs (like 'javascript:') within HTML tag…
CWE-84 Frère
Improper Neutralization of Encoded URI Schemes in a Web Page
This vulnerability occurs when a web application fails to properly sanitize user-supplied input that contains malicious scripts disguised…
CWE-85 Frère
Doubled Character XSS Manipulations
This vulnerability occurs when a web application fails to properly sanitize user input that contains doubled characters, allowing…
CWE-87 Frère
Improper Neutralization of Alternate XSS Syntax
This vulnerability occurs when an application fails to properly sanitize user-supplied input that uses alternative methods to execute…
CWE-184 Pair
Incomplete List of Disallowed Inputs
This vulnerability occurs when a security filter or validation mechanism relies on a 'denylist'—a predefined list of forbidden inputs—but…
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