CWE-1236: Improper Neutralization of Formula Elements in a CSV File

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
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 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.

CWE-1236

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.

Request AI Swarm Pentest

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

Prêt à valider ce qui compte.

Plexicus est Proof-Driven AppSec : findings validés, compréhension contextuelle et remédiation relue — ancrée dans la preuve, scopée avec vous.

Réserver un Pentest

Improper Neutralization of Formula Elements in a CSV File

What is CWE-1236?

Real-world CVEs caused by CWE-1236

Parcours de l'attaquant étape par étape

Vulnerable Other

Secure Other

How to prevent CWE-1236

How to detect CWE-1236

Don't catalog this weakness. Prove it's reachable.

Frequently asked questions

Weaknesses related to CWE-1236

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

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

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

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

Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')

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

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

XML Injection (aka Blind XPath Injection)

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

Further reading

Prêt à valider ce qui compte.

Vérifiez si l'AI Swarm Pentest convient à votre environnement.

Demande reçue. Réservez la prochaine étape.

Sample evidence handover

Server-Side Request Forgery in `webhooks/receiver`