CVE-2019-11358 identifies a critical JavaScript vulnerability in jQuery versions 1.1.4 through 3.3.1 that enables Object.prototype pollution attacks through the jQuery.extend() method. This vulnerability affects jQuery implementations in eZ Platform, Drupal, Backdrop CMS, and numerous other web applications, with a CVSS score of 6.1 (Medium severity) and an EPSS score of 89.9 percentile, indicating high exploitation probability. The vulnerability details reveal that unsanitized source objects containing enumerable proto properties can extend the native Object.prototype when processed through jQuery.extend(true, {}, ...), creating substantial exploit risk for applications that handle user-controlled input. This vulnerability has known public exploits available and affects multiple package ecosystems including npm, NuGet, Maven, RubyGems, and Composer across JavaScript and Java technologies. The technical root cause lies in jQuery's deep object merging functionality, where the extend method fails to properly sanitize prototype chain properties, allowing attackers to pollute the global Object.prototype and potentially achieve remote code execution or application logic bypass. Known exploited vulnerabilities of this type target web applications using jQuery's extend method with untrusted input, particularly affecting content management systems like eZ Platform that bundle vulnerable jQuery versions. The vulnerability impacts over 50 affected packages and libraries, demonstrating widespread exposure across the JavaScript ecosystem. Mitigation steps require upgrading to jQuery 3.4.0 or later, which implements proper prototype pollution protections. Organizations using eZ Platform and similar CMS platforms should prioritize updating bundled jQuery dependencies and implement input validation measures to prevent prototype pollution attacks. Maintaining updated CVE database records and conducting regular vulnerability scanning are essential for identifying similar JavaScript security gaps that could lead to prototype chain manipulation vulnerabilities.