# CVE-2026-87799: Arbitrary file write on LXD host via symlink in migration stream

> An authenticated attacker or malicious migration source can write arbitrary files to the host via symlink exploitation in LXD, leading to full host compromise.

- **Severity:** Critical 9.9 (`CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 28 Sep 2026
- **Updated:** 29 Sep 2026
- **Also known as:** DEBIAN-CVE-2026-87799, GHSA-fmc3-3cpq-6whr, UBUNTU-CVE-2026-87799

## What is CVE-2026-87799?

CVE-2026-87799 is a critical path traversal vulnerability in Canonical LXD, published on 28 Sep 2026. Any signed-in user can exploit it over the network, with no action from the victim.

### Official description

Improper link resolution in the migration receive path in Canonical LXD versions 4.0 and later (fixed in 4.0.14, 5.0.10, 5.21.8 and 6.10) on Linux allows an authenticated client that can create instances or custom storage volumes in a project, or a malicious migration source server, to write attacker-controlled files to arbitrary paths on the target host as root, leading to full host compromise. The attacker does this with a crafted rsync or btrfs send stream that plants a symlink in the transferred volume, such as rootfs or root.img, and then writes through it.

Weakness: CWE-59 (Improper Link Resolution Before File Access)

## Which versions are affected by CVE-2026-87799?


## How do I fix CVE-2026-87799?

No fix has been published for CVE-2026-87799 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-87799 being exploited?

There is no known exploitation of CVE-2026-87799 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-87799 and fix it if it is affected.

What it is: CVE-2026-87799 is a critical path traversal vulnerability in Canonical LXD, published on 28 Sep 2026. Any signed-in user can exploit it over the network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-87799 in the wild and no public exploit code.

Affected product: Canonical LXD. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-87799/ (Markdown: https://insights.sbomify.com/CVE-2026-87799/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-87799
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-87799
- OSV: https://osv.dev/vulnerability/CVE-2026-87799

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-87799/
Summaries are generated and may contain mistakes; the official description above is the record.