Versions of lazysizes prior to 5.2.1-rc1 are vulnerable to Cross-Site Scripting. The video-embed plugin fails to sanitize the following attributes: data-vimeo, data-vimeoparams, data-youtube and data-ytparams. This allows attackers to execute arbitrary JavaScript in a victim's browser if the attacker has control over the vulnerable attributes.

Recommendation

Upgrade to version 5.2.1-rc1 or later.

References

• aFarkas/lazysizes#764
• https://www.npmjs.com/advisories/1493