The AS-path is the ordered list of autonomous systems that a BGP route advertisement has passed through, or claims to have passed through, on its way across the internet. Each router that relays the announcement appends its own autonomous system number, creating a route history that other networks can inspect.
In security terms, the AS-path helps operators judge whether a BGP route looks plausible. An unexpected or unusually short path can indicate route leakage, misconfiguration, or a hijack attempt. Attackers may try to manipulate routing so traffic is redirected through systems they control, which can expose users to interception, denial of service, or malicious content delivery. Defenders monitor AS-path changes to spot detours, and combine that with route origin validation, RPKI, and filtering policies to reject suspicious announcements. In practice, AS-path analysis is one of the quickest ways to notice that trusted traffic may have been pulled onto the wrong network path.