Prototype Pollution in CyberChef via Series Chart CSV Parsing

Compliance Impact

The provided information does not explicitly address how CVE-2026-57439 affects compliance with common standards and regulations such as GDPR or HIPAA.

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Executive Summary

CVE-2026-57439 is a prototype pollution vulnerability in CyberChef, a web application used for encryption, encoding, compression, and data analysis. The vulnerability exists in the Series Chart operation, which accepts __proto__ as a key when parsing user-supplied CSV data. This allows attackers to manipulate the prototype of objects, a technique known as prototype pollution.

By exploiting this, attackers can chain the pollution with other operations such as Parse UDP to inject malicious JavaScript into the HTML output, leading to cross-site scripting (XSS) attacks. The vulnerability was fixed in CyberChef version 11.2.0.

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Impact Analysis

This vulnerability can allow an attacker to inject malicious JavaScript into the HTML output of CyberChef by exploiting prototype pollution in the Series Chart operation. This can lead to cross-site scripting (XSS) attacks, which may result in unauthorized script execution in the context of the affected application.

The impact includes potential manipulation of data processing within CyberChef, low confidentiality and integrity impacts, and the possibility of executing arbitrary scripts that could compromise user data or session information. The CVSS score for this vulnerability is 5.0, indicating a moderate severity.

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Detection Guidance

This vulnerability involves prototype pollution in the Series Chart operation of CyberChef when parsing user-supplied CSV data containing the __proto__ key. Detection would involve identifying if vulnerable versions of CyberChef (prior to 11.2.0) are in use and if malicious CSV inputs containing __proto__ keys are being processed.

There are no explicit detection commands or network signatures provided in the available resources. However, monitoring for usage of CyberChef versions before 11.2.0 and inspecting CSV inputs for the presence of __proto__ keys could help identify potential exploitation attempts.

Since the vulnerability can lead to injection of malicious JavaScript via chained operations, reviewing logs or outputs for unexpected script tags or unusual HTML content in chart outputs might also indicate exploitation.

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Mitigation Strategies

The primary and recommended mitigation step is to upgrade CyberChef to version 11.2.0 or later, where this prototype pollution vulnerability has been fixed.

No workarounds are available according to the security advisory, so upgrading is essential to prevent exploitation.

Additionally, avoid processing untrusted CSV inputs containing __proto__ keys or chaining the Series Chart operation with other operations like Parse UDP until the upgrade is applied.

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