CVE-2020-7642: 
JavaScript vulnerability analysis and mitigation

CVE-2020-7642 affects lazysizes through version 5.2.0, specifically its video-embed plugin. The vulnerability was discovered and disclosed on April 21, 2020, impacting the lazysizes package, which is a fast, SEO-friendly and self-initializing lazyloader for images, iframes, scripts, and widgets (NVD, Snyk).

The vulnerability is a Cross-site Scripting (XSS) issue that occurs due to unsafe usage of innerHTML in the video-embed plugin. The security flaw exists because several attributes are not properly sanitized: data-vimeo, data-vimeoparams, data-youtube, and data-ytparams. These unsanitized attributes can be exploited to inject malicious JavaScript code (Snyk).

When exploited, this vulnerability allows attackers to execute malicious JavaScript through the unsanitized attributes in the video-embed plugin. This could lead to the execution of arbitrary JavaScript code in the context of the affected web application (NVD, Snyk).

The vulnerability has a CVSS v3.1 Base Score of 5.7 (Medium severity). Exploitation requires user interaction and low privileges. Snyk has confirmed the existence of a proof-of-concept exploit for this vulnerability (Snyk).

The recommended mitigation is to upgrade lazysizes to version 5.2.1-rc1 or higher, which contains the security fix. A fix was implemented through input validation by adding a regValidParam check to verify the safety of the video ID and parameters (GitHub, Snyk).