Canonical MicroCeph CVE-2026-10720

Exploitation requires possession of either a trusted cluster mTLS certificate (as held by enrolled MicroCeph cluster members) or a valid cluster join token - these are the only two credential types the description identifies as granting the necessary trust level. The attacker must have network access to the MicroCeph remote-import API endpoint. The vulnerability is hard-bounded by snap confinement: only files within /var/snap/microceph can be reached, not arbitrary filesystem paths. Default deployments with properly managed join tokens limit exposure to trusted-insider or compromised-node scenarios. The CVSS 4.0 AT:P metric confirms this specific precondition must be present. Exploitation is NOT possible by unauthenticated network actors or by users who have not been granted a join token or enrolled as a cluster member.

The CVSS 4.0 base score of 5.1 (Medium) is driven primarily by PR:H - exploitation requires possession of a trusted cluster mTLS certificate held by an enrolled cluster member, or a valid join token. This meaningfully restricts the attacker population to insiders, compromised cluster nodes, or parties who obtained a join token through mismanagement or social engineering. However, the subsequent-system impact metrics (SI:H, SA:H) reveal that once this threshold is crossed, the attacker can cause high-integrity and high-availability damage to the broader cluster, not just the local node. The AT:P metric confirms a specific precondition must be met. No EPSS data is available, and the vulnerability is not listed in CISA KEV, nor is any public exploit identified. Real-world risk is elevated in multi-tenant or federated deployments where join tokens are distributed to many parties or where cluster membership is not tightly controlled. The snap confinement to /var/snap/microceph limits blast radius compared to a fully unconfined traversal, but cluster configuration files and daemon state within that boundary are sufficient to cause operational disruption.

A malicious or compromised cluster member possessing a valid mTLS certificate sends a crafted PUT request to the remote-import API with a name or LocalName parameter containing a path traversal sequence such as ../state. The unpatched API constructs a filesystem path from the unsanitized input, writing or overwriting files in unintended directories within /var/snap/microceph, which corrupts cluster configuration state and causes one or more MicroCeph daemons to crash or behave erroneously. No public exploit code exists at time of analysis, but the PR #758 test suite explicitly documents the exact traversal strings (../state, .., remote/name) that bypass the unpatched validation, lowering the barrier for a motivated attacker.