8.7

CVSS Score

3.1

-

CVSS Score

Basic Information

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CVE-2026-23954

CVE-2026-23954: Incus container image templating arbitrary host file read and write

Incus is a system container and virtual machine manager. Versions 6.21.0 and below allow a user with the ability to launch a container with a custom image (e.g a member of the ‘incus’ group) to use directory traversal or symbolic links in the templating functionality to achieve host arbitrary file read, and host arbitrary file write. This ultimately results in arbitrary command execution on the host. When using an image with a metadata.yaml containing templates, both the source and target paths are not checked for symbolic links or directory traversal. This can also be exploited in IncusOS. A fix is planned for versions 6.0.6 and 6.21.0, but they have not been released at the time of publication.

(GitHub Advisory)

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CVE-2026-23954

CVE-2026-23954:

8.7

CVSS Score

3.1

-

CVSS Score

Basic Information

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Technical Details

Package Name	Ecosystem	Vulnerable Versions	First Patched Version
github.com/lxc/incus/v6/cmd/incusd	go	>= 6.1.0, <= 6.20.0
github.com/lxc/incus/v6/cmd/incusd	go	<= 6.0.5

Technical Details

Vulnerability Intelligence
Miggo AI

Root Cause Analysis

The analysis of the provided patch file templates_arbitrary_write.patch clearly indicates that the function lxc.templateApplyNow in internal/server/instance/drivers/driver_lxc.go is the primary location of the vulnerability. The patch shows the replacement of insecure file path handling (filepath.Join, os.Create, os.ReadFile) with safer, chrooted alternatives (os.OpenRoot, rootPath.Create, templatesPathRoot.ReadFile). The vulnerability stems from the lack of validation on user-controlled paths provided in the metadata.yaml file of a container image, specifically the template source and destination paths. The original code concatenated these paths without checking for directory traversal characters (../) or resolving symbolic links safely, allowing an attacker to read from and write to arbitrary locations on the host filesystem. The identified function lxc.templateApplyNow is the exact place where these malicious paths are processed and used in file operations, making it the vulnerable function that would appear in a runtime profile during exploitation.

Vulnerable functions

lxc.templateApplyNow

internal/server/instance/drivers/driver_lxc.go

The function `templateApplyNow` is responsible for applying templates from an image's `metadata.yaml` when a container is started. It was found to be vulnerable to path traversal and symbolic link attacks. The function constructs file paths for both reading template source files and writing the output to the container's filesystem without proper sanitization. An attacker could craft a `metadata.yaml` with a `template` path containing directory traversal sequences (`../`) to read arbitrary files from the host filesystem (e.g., `../../../../../../../../etc/shadow`). Additionally, by creating a symbolic link inside the container image that points to the host's root directory (`/`), an attacker could specify a target path that resolves to a location outside the container's intended rootfs, allowing arbitrary file writes on the host. The vulnerability was fixed by using `os.OpenRoot` to create a chroot-like jail for all file operations, preventing access outside the designated container and template directories.

Vulnerability Intelligence
Miggo AI

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WAF Rule

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Reasoning

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