Prototype Pollution in cleverbrush Deep Object Extension

A vulnerability has been found in cleverbrush framework and deep up to 4.4.0. This impacts the function deepExtend of the file libs/deep/src/deepExtend.ts. The manipulation leads to improperly controlled modification of object prototype attributes. Remote exploitation of the attack is possible. The exploit has been disclosed to the public and may be used. Upgrading to version 4.4.1 will fix this issue. The identifier of the patch is 810398c1308c500c3b8b6af380b5a89371389327. You should upgrade the affected component.

Casky was already ahead

This CVE exploits attack patterns that Casky's 323matched skills already investigate — long before this vulnerability was disclosed. Claude's reasoning model maps these techniques to MITRE ATT&CK, so practitioners who ran these skills have already seen the threat behaviour in their findings.

Analysis

CVE-2026-78654 is a prototype pollution vulnerability in the cleverbrush framework's deepExtend function that allows remote attackers to improperly modify JavaScript object prototype attributes. This high-severity flaw (CVSS 7.3) affects cleverbrush versions up to 4.4.0 and poses significant risk to any application using this library for object manipulation or merging operations. The vulnerability enables attackers to inject malicious properties into Object.prototype, potentially affecting all objects created after exploitation—a capability that can lead to privilege escalation, data manipulation, or remote code execution depending on how the application uses extended objects. Organizations running dependent applications should immediately upgrade to version 4.4.1 or later, as this vulnerability has been publicly disclosed and active exploitation is possible.

Casky's 323 mapped security skills leverage Claude's extended reasoning to detect the attack patterns associated with TA0001 (Reconnaissance) and TA0043 (Reconnaissance via proxy servers/infrastructure enumeration) by analyzing both CWE-94 (Improper Control of Generation of Code) and CWE-1321 (Improperly Controlled Modification of Object Prototype Attributes in JavaScript). Practitioners using Casky would observe detection signals including: suspicious deepExtend function calls with untrusted input sources, object property chains showing unexpected prototype mutations, runtime modifications to Object.prototype or constructor properties, and behavioral indicators of code injection attempts. The platform's skill mapping to MITRE ATT&CK techniques helps security teams correlate these findings with reconnaissance patterns and initial access vectors, enabling them to identify whether attackers are probing for vulnerable versions or actively attempting to manipulate application state through prototype pollution chains.

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Casky Risk Score

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EPSS Probability

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Shodan Exposure

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GreyNoise Signal

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323 Casky skills cover this attack pattern

These skills use Claude AI's reasoning model to surface findings in the same attack categories as CVE-2026-78654.

Abuse of Public-Facing API: Mobile API Abuse

mobile security · low

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abusing-dpapi-for-credential-access

red teaming · high

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abusing-shadow-credentials-for-privesc

red teaming · high

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MITRE ATT&CK Techniques

TA0001 TA0043

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