CVE-2026-63125: Incus Container Manager Discloses 7 CVSS 9.9 Critical Vulnerabilities; Container Isolation Effectively Broken

Linux container manager Incus disclosed 7 critical vulnerabilities in one batch. Core CVE-2026-63125 scores 9.9. A project-level user can obtain root code execution on the host via an image backup.yaml symlink attack, breaking container isolation. Treat multi-tenant deployments as an emergency patch event. Officially fixed in 7.3.0.

Linux container manager Incus disclosed 7 critical-severity vulnerabilities in a concentrated dump on August 22–23. All score CVSS 9.9. Core CVE is CVE-2026-63125. An unprivileged user with only project-level permissions (`can_create_images` and `can_create_instances`) can craft an image `backup.yaml` containing a symlink and execute arbitrary code as root on the host. Container isolation is considered broken on affected versions. Multi-tenant Incus deployments face immediate risk. Official fix shipped in Incus 7.3.0.

Incident Overview

Incus is a Linux container and VM manager, a primary fork of LXD. Used widely for multi-tenant container platforms, edge deployments, self-hosted clouds, and developer sandboxes. Design goal: isolate resources across projects so users create and manage instances only inside their own namespace. CVE-2026-63125 plus six concurrently disclosed bugs show that below 7.3.0, a project-level user can combine image import and instance create—two ordinary operations—to bypass project boundaries and obtain host-root-equivalent privileges. Enigma Global listed this with concurrent Nezha Monitoring, Apache Camel, and StackGres issues among this week's highest-priority multi-tenant isolation breaks.

Technical Details

CVE-2026-63125 is a `backup.yaml` symlink attack. Incus describes image metadata via `backup.yaml`. Import accesses paths declared in `backup.yaml` during extract and restore. An attacker holding `can_create_images` and `can_create_instances` in a project can craft an image with a specially formed `backup.yaml`, then trigger instance creation against that image. If a path entry in `backup.yaml` is a symlink, the privileged restore process follows it and reads or writes arbitrary locations on the host filesystem. Result: root code execution. The other six CVSS 9.9 bugs cover distinct privilege-escalation and bypass paths. Combined they form a complete isolation-break chain.

Impact Assessment

CVSS: 9.9 (Critical). Attack vector: network or local (depends on management API exposure). Attack complexity: low. Privileges required: low (ordinary project-level user). User interaction: none. PoC status: no complete PoC observed; technical details published with the advisory; exploit development cost is very low. Known in-the-wild: no 0day exploitation observed. Impact surface: all Incus deployments before 7.3.0—especially multi-tenant setups, research/education container services, self-hosted multi-user container clouds, and internal Incus-based dev platforms.

Affected Scope and Versions

• Incus: all versions below 7.3.0
• Trigger: multi-tenant or project-level isolation enabled, and project users hold `can_create_images` and `can_create_instances`
• Official fix: Incus 7.3.0
• The six companion CVSS 9.9 bugs are also fixed in 7.3.0. Upgrade once.

Remediation

• Inventory every Incus instance version immediately. Schedule an emergency upgrade window for all pre-7.3.0 deployments.
• Priority P0: upgrade all Incus instances exposing the management API to 7.3.0. Validate project isolation policy and import/export flows in a test environment first.
• Multi-tenant instances that cannot upgrade immediately: temporarily tighten project-level permissions. Keep `can_create_images` and `can_create_instances` only for trusted admins. Revoke those permissions from ordinary project users.
• Isolate the management API: restrict Incus management ports to a trusted admin network. Block external and cross-project access.
• Enable Incus audit logs. Watch `backup.yaml` import and instance-create events. Flag anomalous image references from in-project users.
• Deploy host file-integrity monitoring. Watch unexpected changes under `/var/lib/incus`, `/etc/incus`.
• During the pre-upgrade window, deploy host IDS rules that monitor anomalous process chains from container processes spawning a host shell.
• After upgrade, review import/create event logs from the patch window. Confirm no cross-project privilege escalation occurred.

Detection Rules

• Alert on Incus audit-log import requests whose `backup.yaml` contains unconventional symlink paths
• Alert when a project-level user triggers multiple instance creates or image imports in a short window
• Alert on unexpected files created or modified by the `incusd` process on the host filesystem
• Alert when Incus management API source IPs deviate from known admin subnets
• Host HIDS: monitor unexpected writes to common container-escape targets (`/etc/crontab`, `/etc/passwd`, `/root/.ssh/authorized_keys`)

Once container isolation breaks, the multi-tenant cloud security model is pierced. Treat Incus deployments before 7.3.0 as an emergency patch event. Rebuild the multi-tenant trust chain with three layers: dependency scanning, container image allowlists, and least privilege.

References

• Enigma Global: Daily Threat Intelligence Digest 2026-08-23
• CVE Brief: August 23 2026 daily summary
• The Hacker Wire: Critical Privilege Escalation in StackGres Operator