IMDS
acronymcloudsecurity
Instance Metadata Service: the link-local endpoint (169.254.169.254) where a cloud instance asks about itself - and collects its temporary credentials.
The crown-jewel target of SSRF attacks; IMDSv2's session tokens exist because of that history.
The instance metadata service is a link-local endpoint a cloud instance queries to learn about itself, including temporary credentials for the role it runs as. Its convenience is exactly its danger.
Because it is reachable from the instance with no authentication, any vulnerability that lets an attacker make the instance issue a request on their behalf, most commonly server-side request forgery, retrieves those credentials. That is the mechanism behind several very large cloud breaches. The mitigation is the second version of the protocol, which requires a token obtained by a PUT with a hop limit that ordinary forgery cannot satisfy, and enforcing it rather than merely enabling it is the part that gets missed.