That's not really how Lemmy works, it's more like Reddit, where you'd probably want to look at communities. But I've not seen anyone announce any new vulns here, people just post links to articles about them.
Searching for communities from the db0 instance should get you a bunch related to cybersecurity and infosec (only reccomending as some other instances have defederated from the .ml instance you're posting from/in). If I have some time later I'll edit this post with some.
EDIT: Posting from my phone, so apologies that these are direct links rather than in the "home instance agnostic" format
CyberSec communities: https://lemmy.ml/c/cryptography https://infosec.pub/c/cybersecurity https://sh.itjust.works/c/cybersecurity https://lemmy.zip/c/databreaches https://infosec.pub/c/pulse_of_truth https://infosec.pub/c/securitynews
Sysadmin communities: https://lemmy.world/c/sysadmin https://lemmy.ml/c/sysadmin
Privacy (usually tech related) communities: https://lemmy.ca/c/privacy https://lemmy.ml/c/privacy https://lemmy.world/c/privacy https://programming.dev/c/privacy https://links.hackliberty.org/c/privacy