CVE-2026-6621: Prototype Pollution in 1024bit extend-deep

The National Vulnerability Database (NVD) has identified CVE-2026-6621, a high-severity (CVSS 7.3) vulnerability impacting 1024bit extend-deep up to version 0.1.6. This flaw, categorized under CWE-94 (Improper Control of Generation of Code) and CWE-1321 (Improperly Controlled Modification of Object Prototype Attributes (‘Prototype Pollution’)), stems from an improperly controlled modification of object prototype attributes via the __proto__ argument in the index.js file. This is classic prototype pollution, a pernicious vulnerability that allows attackers to inject or modify properties of an object’s prototype, potentially leading to arbitrary code execution or denial of service.

Remote exploitation of this vulnerability is possible, and the NVD notes that an exploit has been publicly disclosed and may be actively utilized. The critical context here is that the project’s code repository has been inactive for many years, meaning official patches are highly unlikely. This leaves any systems still using this library exposed to significant risk.

Defenders must understand that despite the library’s age, it could still be embedded within larger, more current applications as a dependency. The attacker’s calculus is straightforward: find vulnerable instances of this unmaintained library and leverage the public exploit. CISOs should prioritize identifying any internal or third-party applications that incorporate 1024bit extend-deep and either deprecate them or implement robust input validation to neutralize the __proto__ manipulation vector.