CVE-2026-23520: Arcane Has a Command Injection in Arcane Updater Lifecycle Labels That Enables RCE

Arcane’s updater service supported lifecycle labels com.getarcaneapp.arcane.lifecycle.pre-update and com.getarcaneapp.arcane.lifecycle.post-update that allowed defining a command to run before or after a container update. The label value is passed directly to /bin/sh -c without sanitization or validation.

Because any authenticated user (not limited to administrators) can create projects through the API, an attacker can create a project that specifies one of these lifecycle labels with a malicious command. When an administrator later triggers a container update (either manually or via scheduled update checks), Arcane reads the lifecycle label and executes its value as a shell command inside the container.

If the container is configured with host volume mounts in its Compose definition, the executed command may be able to read from or write to the host filesystem through the mounted paths. This can enable data theft and, in some configurations, escalation to full host compromise (for example, if /var/run/docker.sock is mounted).