"Microsoft Patches Azure Cross-Tenant Data Access Flaw"

Microsoft has recently silently fixed an important-severity security flaw in its Azure Container Service (ACS) after an external researcher warned that a buggy feature allowed cross-tenant network bypass attacks.  The vulnerability effectively removed the entire network and identity perimeter around internet-isolated Azure Cognitive Search instances and allowed cross-tenant access to the data plane of ACS instances from any location, including instances without any explicit network exposure.  According to the security researcher who discovered the flaw, Microsoft silently fixed it at the end of August 2022, approximately six months after it was first reported.  The exposure, nicknamed ACSESSED, impacted all Azure Container Service instances that enabled the “Allow access from portal” feature.  The researcher warned that by enabling that feature, customers effectively allowed cross-tenant access to the data plane of their ACS instances from any location, regardless of the actual network configurations of the latter.  The researcher noted that this included instances exposed exclusively on private endpoints, as well as instances without any explicit network exposure.  The researcher noted that by the simple click of a button, customers were able to turn on a vulnerable feature, which removed the entire network perimeter configured around their ACS instances without providing any real identity perimeter (i.e. anybody could generate a valid access token for ARM).  Microsoft paid the researcher a $10,000 bounty and elevated the risk level from moderate to important because of the cross-tenant risk and ease of exploitation.

SecurityWeek reports: "Microsoft Patches Azure Cross-Tenant Data Access Flaw"