CVE-2026-46354: Coder: PKCS#7 signature bypass in Azure instance identity allows unauthenticated agent token theft

azureidentity.Validate() verifies that the PKCS#7 signer certificate chains to a trusted Azure CA but never verifies the PKCS#7 signature itself. An attacker can embed a legitimate Azure certificate alongside arbitrary content e.g. {"vmId":"<target>"} and the forged vmId will be accepted returning the victim workspace agent’s session token.

No authentication is required. The attacker only needs to know a target VM’s vmId which is a UUIDv4.

that’s a practical limitation which would typically require prior access to be exploited