What happened
Claroc searched passive DNS for cf.metaaiusercontent.com and found more than 6,800 Muse share links, because the conversation title was placed in the URL's subdomain. The pages included CEO sales reports, small-business loan applications, bank fraud records and staff vacation calendars.
Why it matters
Anyone who knew the domain could reach shared chats without receiving the link, and Meta says it has paused sharing while it considers changing how links are discovered.
WHO IT HITSEmployees and executives who paste sensitive material into Meta's Muse chat and use its share button may have had that content exposed to anyone who queried passive DNS records, with the risk extending to HR, finance and deal-preparation documents.
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Muse generated share links by combining a conversation title with a random identifier, as in home-sale-budget-9f21c8a3.cf.metaaiusercontent.com. The flaw was that the title sat in the subdomain, which can be recorded externally through DNS, the system that resolves a website's destination.
Because passive DNS services collect and expose those historical records, a lookup on cf.metaaiusercontent.com surfaced both the topic and the full address, letting people who never received a link open the page. Claroc reported the issue, which it named GhostShares, to Meta's vulnerability program on October 8, 2026.
Claroc said it found no evidence the exposed information had been misused, but it advised checking who can view shared material before using an AI tool's sharing feature. Meta's reply to Ars Technica indicates the suspension lasts while it studies a change to how links are found.
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