Netskope Threat Labs

BROWSER-IE Microsoft Internet Explorer JavaScript engine downgrade detected

IPS-SWG

1 SID: 48699

First seen
September 2022
Last seen
October 2026

Detects web content that forces Internet Explorer into legacy document modes or the deprecated JScript engine through compatibility declarations. This activity signals compatibility workarounds rather than an attack, but downgrading the engine weakens the browser's protections and warrants review of the page that requests it.