GHSA-VGHH-5RFX-XHQ8: CVE-2026-48749: Arbitrary Host File Read and Write via Malicious Image Symlink in Canonical LXD and Incus

CVE-2026-48749: Arbitrary Host File Read and Write via Malicious Image Symlink in Canonical LXD and Incus Vulnerability ID: GHSA-VGHH-5RFX-XHQ8 CVSS Score: 9.9 Published: 2026-11-06 CVE-2026-48749 (tracked as GHSA-vghh-5rfx-xhq8 for LXD and GHSA-2q3f-q5pq-g8wv for Incus) is a critical container escape vulnerability in the Canonical LXD and Linux Containers Incus system container managers. By importing a specially crafted container image archive containing duplicate tar member headers, an authenticated attacker can replace the instance rootfs directory with a symbolic link pointing to the underlying host root filesystem. When performing file operations on a stopped container, the privileged forkfile helper binary resolves the symbolic link without confinement and chroots directly into the host filesystem, granting arbitrary root-level file read and write access. TL;DR A tar extraction validation bypass and unconfined symlink resolution flaw in Canonical LXD and Incus allows authenticated users with image import permissions to replace a container's rootfs directory with a symlink to the host root filesystem, resulting in arbitrary file read, arbitrary file write, and complete host compromise as root. ⚠️ Exploit Status: POC Technical Details CVE ID: CVE-2026-48749 (GHSA-vghh-5rfx-xhq8 / GHSA-2q3f-q5pq-g8wv) Weakness Class: CWE-73: External Control of File Name or Path CVSS v3.1 Score: 9.9 CRITICAL (CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H) EPSS Score: 0.78% (56.22nd Percentile) Attack Vector: Authenticated API / Malicious Container Image Import Security Impact: Container Escape via Arbitrary Host File Read and Write as Root Exploit Status: Public Proof-of-Concept (PoC) Available CISA KEV Status: Not Listed Affected Systems Canonical LXD Linux Containers Incus LXD: >= 4.0.0, < 4.0.11 (Fixed in: 4.0.11) LXD: >= 5.0.0, < 5.0.7 (Fixed in: 5.0.7) LXD: >= 5.1.0, < 5.21.5 (Fixed in: 5.21.5) LXD: >= 6.0.0, < 6.9.0 (Fixed in: 6.9.0) Incus: < 7.2.0 (Fixed in: 7.2.0) Code Analysis Commit: 190e245 Canonical LXD security patch for rootfs and templates path validation (CVE-2026-48749). Commit: 254b85c Canonical LXD security patch enforcing symlink checks and path confinement. Commit: 3dbf4ce Canonical LXD backport commit addressing GHSA-vghh-5rfx-xhq8. Commit: 4cd6334 Canonical LXD commit updating instance rootfs access methods. Commit: 51dc11e Canonical LXD commit confining subdirectory operations within instance paths. Commit: 62bcee5 Canonical LXD patch preventing symlink traversal in instance drivers. Commit: 8751ea6 Canonical LXD backport patch for CVE-2026-48749. Commit: b499ec4 Canonical LXD commit hardening template and rootfs path resolution. Commit: e2aeca6 Canonical LXD fix for rootfs symlink resolution in forkfile operations. Commit: edb6d99 Canonical LXD commit introducing subPath symlink rejection. Exploit Details GitHub Security Advisory (LXD): Official Canonical LXD advisory containing functional shell script Proof-of-Concept demonstrating arbitrary host file read and write. GitHub Security Advisory (Incus): Official Linux Containers Incus advisory detailing the rootfs symlink arbitrary file read/write exploit. Mitigation Strategies Upgrade Canonical LXD and Linux Containers Incus to the latest patched point releases. Restrict LXD/Incus Unix socket membership and remote REST API access to trusted host administrators only. Disable custom image imports for untrusted or multi-tenant project users until patches are applied. Monitor storage pool directories for symbolic links named 'rootfs' or 'templates' and audit forkfile helper executions. Remediation Steps: Identify all hosts running Canonical LXD (< 4.0.11, < 5.0.7, < 5.21.5, < 6.9.0) or Incus (< 7.2.0). Audit storage pool directories using 'find /var/lib/lxd/storage-pools/ -maxdepth 3 -type l -name rootfs' and 'find /var/lib/incus/storage-pools/ -maxdepth 3 -type l -name rootfs' to verify no malicious instances exist. Apply vendor updates via snap, apt, or distribution package managers to upgrade LXD to 4.0.11 / 5.0.7 / 5.21.5 / 6.9.0+ or Incus to 7.2.0+. Restart the LXD or Incus daemon if not automatically handled by the package manager and verify version status. References GitHub Security Advisory: GHSA-vghh-5rfx-xhq8 (Canonical LXD) GitHub Security Advisory: GHSA-2q3f-q5pq-g8wv (LXC Incus) NVD Vulnerability Detail: CVE-2026-48749 CVE.org Official Record: CVE-2026-48749 Canonical LXD Source Repository Announcing Incus 7.2 Read the full report for GHSA-VGHH-5RFX-XHQ8 on our website for more details including interactive diagrams and full exploit analysis.