Style Dictionary versions from 4.3.0 up to but not including 5.4.4 contain a prototype pollution vulnerability in the convertTokenData utility function. This vulnerability allows a malicious user to inject tokens with keys like '{__proto__.foo}', which pollutes the global Object.prototype. The vulnerability affects direct usage of convertTokenData as well as indirect usage via the Expand API or the transform lifecycle. The impact is highest when Style Dictionary is integrated into NodeJS server applications, moderate for web applications, and low when token data is tightly controlled. A patch is available in version 5.4.4. Workarounds include sanitizing token data to reject keys containing '__proto__' and disabling the expand feature.