Because Symantec uses a filter driver to intercept all system I/O, just emailing a file to a victim or sending them a link to an exploit is enough to trigger it – the victim does not need to open the file or interact with it in anyway. Because no interaction is necessary to exploit it, this is a wormable vulnerability with potentially devastating consequences to Norton and Symantec customers.
An attacker could easily compromise an entire enterprise fleet using a vulnerability like this. Network administrators should keep scenarios like this in mind when deciding to deploy Antivirus, it’s a significant tradeoff in terms of increasing attack surface.
If you use a Symantec or Norton product, now would be a good time to update.
Source: High-severity bugs in 25 Symantec/Norton products imperil millions | Ars Technica