Wiz Discloses Cross-Tenant CosmosEscape Flaw in Azure Cosmos DB

Wiz researchers have disclosed a now-patched Azure Cosmos DB vulnerability they call CosmosEscape, and the interesting part is not just that one more cloud bug got fixed, it is what the chain reached. As Reuters reported, the flaw would have allowed a hacker to remotely access any user's data on the service, and Microsoft told the outlet the issue has been fully addressed with 'no evidence of customer impact.'

The technical picture in the Wiz write-up is worth reading twice. Their team was experimenting with Gremlin, a graph query language supported by Cosmos DB, and noticed an unusual .NET exception where they expected the usual JVM behaviour. That told them Cosmos DB was running a custom .NET-based Gremlin engine, and the engine translated queries into .NET code without adequately restricting reflection. From that seed they escaped the sandbox and obtained what Wiz calls the Cosmos Master Key, a signing key that was not scoped to a single customer or region and worked across SQL, MongoDB, Cassandra and Gremlin API formats. That key, according to the researchers, could be used to retrieve the primary key of any Cosmos DB account on demand, giving full read and write access.

The blast radius is why this reads as more than another bug bounty write-up. Cosmos DB is not just a customer-facing database, it underpins Microsoft services including Microsoft Entra ID, Microsoft Teams and Microsoft Copilot, so a successful chain would have extended into Microsoft's own backend rather than only enterprise tenants. It also lands roughly five years after Wiz's 2021 ChaosDB finding in the same service, which is going to raise pointed questions inside customers about whether multi-tenant isolation on this particular backend is as strong as the marketing implies.

The honest caveat is that this is a single-vendor account of what a chain could have done, not a record of what it did. Microsoft's line, per the reporting, is that no unauthorised activity was seen outside the researcher's own testing, and the long-term fix rollout completed across all regions in July 2026. What the reporting does not give you is a timeline for how long the reflection weakness sat exploitable, or which internal Microsoft services would have been directly reachable via the Master Key.

For security leaders the practical read is to treat this less as patch-and-move-on and more as a prompt to audit which of your AI and data workloads sit on Cosmos DB, rotate keys, and pull the disclosure into your next tabletop as the exact class of cross-tenant sandbox-escape scenario that a shared-fate cloud model is supposed to make impossible.