CWE-1236 Base Incomplet

Improper Neutralization of Formula Elements in a CSV File

This vulnerability occurs when an application writes user-supplied data into a CSV file without properly sanitizing special characters. Spreadsheet programs like Excel or Google Sheets interpret…

Définition

What is CWE-1236?

This vulnerability occurs when an application writes user-supplied data into a CSV file without properly sanitizing special characters. Spreadsheet programs like Excel or Google Sheets interpret entries starting with '=' as executable formulas, which can lead to malicious command execution when the file is opened.
Many applications export data to CSV files for easy viewing in spreadsheet software. However, these programs treat cells beginning with characters like =, +, -, or @ as formulas. If an attacker can inject data like `=HYPERLINK("http://malicious-site.com", "Click")` or a formula that calls external scripts, simply opening the CSV file can trigger data theft, remote code execution, or other harmful actions on the user's machine. Developers often overlook this risk because CSV files are seen as simple data dumps, not executable content. To prevent this, you must sanitize or escape formula-initiating characters in all user-controlled fields before writing them to a CSV. This ensures that data is displayed as static text, not as an active command, when the file is imported into a spreadsheet application.
Impact réel

Real-world CVEs caused by CWE-1236

  • CVE-2019-12134

    Low privileged user can trigger CSV injection through a contact form field value

  • CVE-2019-4521

    Cloud management product allows arbitrary command execution via CSV injection

  • CVE-2019-17661

    CSV injection in content management system via formula code in a first or last name

Comment les attaquants l'exploitent

Parcours de l'attaquant étape par étape

  1. 1

    Identifier un chemin de code qui traite des entrées non fiables sans validation.

  2. 2

    Élaborer une charge utile qui exploite le comportement non sécurisé — injection, traversal, débordement ou abus de logique.

  3. 3

    Délivrer la charge utile via une requête normale et observer la réaction de l'application.

  4. 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 Other

Hyperlinks or other commands can be executed when a cell begins with the formula identifier, '='

Vulnérable Other 
=HYPERLINK(link_location, [friendly_name])
Charge utile de l'attaquant

Hyperlinks or other commands can be executed when a cell begins with the formula identifier, '='

Charge utile de l'attaquant Other 
=HYPERLINK(link_location, [friendly_name])
Exemple de code sécurisé

Secure Other

Stripping the leading equals sign, or simply not executing formulas from untrusted sources, impedes malicious activity.

Sécurisé Other 
HYPERLINK(link_location, [friendly_name])
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-1236

  • Implementation When generating CSV output, ensure that formula-sensitive metacharacters are effectively escaped or removed from all data before storage in the resultant CSV. Risky characters include '=' (equal), '+' (plus), '-' (minus), and '@' (at).
  • Implementation If a field starts with a formula character, prepend it with a ' (single apostrophe), which prevents Excel from executing the formula.
  • Architecture and Design Certain implementations of spreadsheet software might disallow formulas from executing if the file is untrusted, or if the file is not authored by the current user.
Signaux de détection

How to detect CWE-1236

SAST High

Exécuter une analyse statique (SAST) sur le code source à la recherche du motif non sécurisé dans le flux de données.

DAST Moderate

Exécuter des tests de sécurité applicative dynamique (DAST) contre le point de terminaison en ligne.

Runtime Moderate

Surveiller les journaux runtime pour détecter des traces d'exception inhabituelles, des entrées malformées ou des tentatives de contournement d'autorisation.

Code review Moderate

Revue de code : signaler tout nouveau code qui traite les entrées de cette surface sans utiliser les helpers du framework validés.

Correction automatique Plexicus

Plexicus détecte automatiquement CWE-1236 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.

Obtenir une démo Essayer Plexicus gratuitement
Questions fréquentes

Frequently asked questions

Qu'est-ce que CWE-1236 ?

This vulnerability occurs when an application writes user-supplied data into a CSV file without properly sanitizing special characters. Spreadsheet programs like Excel or Google Sheets interpret entries starting with '=' as executable formulas, which can lead to malicious command execution when the file is opened.

Quelle est la gravité de CWE-1236 ?

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-1236 ?

MITRE lists the following affected platforms: Not OS-Specific, Not Architecture-Specific, Other.

Comment puis-je prévenir CWE-1236 ?

When generating CSV output, ensure that formula-sensitive metacharacters are effectively escaped or removed from all data before storage in the resultant CSV. Risky characters include '=' (equal), '+' (plus), '-' (minus), and '@' (at). If a field starts with a formula character, prepend it with a ' (single apostrophe), which prevents Excel from executing the formula.

Comment Plexicus détecte et corrige CWE-1236 ?

Le moteur SAST de Plexicus reconnaît la signature de flux de données de CWE-1236 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-1236 ?

MITRE publie la définition canonique à https://cwe.mitre.org/data/definitions/1236.html. Vous pouvez également consulter la documentation OWASP et NIST pour des conseils adjacents.

Faiblesses associées

Weaknesses related to CWE-1236

CWE-74 Parent

Improper Neutralization of Special Elements in Output Used by a Downstream Component ('Injection')

This vulnerability occurs when an application uses untrusted external input to build a command, query, or data structure for another…

CWE-75 Frère

Failure to Sanitize Special Elements into a Different Plane (Special Element Injection)

This vulnerability occurs when an application fails to properly filter or encode user-supplied data containing special characters or…

CWE-77 Frère

Improper Neutralization of Special Elements used in a Command ('Command Injection')

This vulnerability occurs when an application builds a system command using untrusted user input without properly sanitizing it. An…

CWE-78 Frère

Improper Neutralization of Special Elements used in an OS Command ('OS Command Injection')

OS Command Injection occurs when an application builds a system command using untrusted, external input without properly sanitizing it.…

CWE-79 Frère

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-88 Frère

Improper Neutralization of Argument Delimiters in a Command ('Argument Injection')

This vulnerability occurs when an application builds a command string for execution by another component, but fails to properly separate…

CWE-89 Frère

Improper Neutralization of Special Elements used in an SQL Command ('SQL Injection')

SQL Injection occurs when an application builds a database query using untrusted user input without properly sanitizing it. This allows an…

CWE-91 Frère

XML Injection (aka Blind XPath Injection)

XML Injection occurs when an application fails to properly validate or escape user-controlled input before including it in XML documents…

CWE-917 Frère

Improper Neutralization of Special Elements used in an Expression Language Statement ('Expression Language Injection')

Expression Language Injection occurs when an application uses untrusted, external input to build an expression language statement—common…

Ressources

Further reading

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