# CVE-2026-40242: Arcane Unauthenticated SSRF with Conditional Response Reflection in Template Fetch Endpoint

> Unauthenticated attackers can exploit an SSRF vulnerability in the template fetch endpoint to read internal server responses.

- **Severity:** High 7.2 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:L/A:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 10 Apr 2026
- **Updated:** 13 Apr 2026
- **Also known as:** GHSA-ff24-4prj-gpmj, GO-2026-5356

## What is CVE-2026-40242?

CVE-2026-40242 is a high-severity server-side request forgery vulnerability in getarcaneapp arcane, published on 10 Apr 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

Arcane is an interface for managing Docker containers, images, networks, and volumes. Prior to 1.17.3, the /api/templates/fetch endpoint accepts a caller-supplied url parameter and performs a server-side HTTP GET request to that URL without authentication and without URL scheme or host validation. The server's response is returned directly to the caller. type. This constitutes an unauthenticated SSRF vulnerability affecting any publicly reachable Arcane instance. This vulnerability is fixed in 1.17.3.

Weakness: CWE-918 (Server-Side Request Forgery)

## Which versions are affected by CVE-2026-40242?

3 open source packages ship an affected version, including github.com/getarcaneapp/arcane/backend. It affects 1 product.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `github.com/getarcaneapp/arcane/backend` | Go | All versions | 1.17.3 |
| `github.com/getarcaneapp/arcane/backend` | Go | All versions | 1.17.3 |
| `github.com/getarcaneapp/arcane/backend` | Go | All versions | 1.17.3 |

Products: Getarcane Arcane.

## How do I fix CVE-2026-40242?

Upgrade github.com/getarcaneapp/arcane/backend to 1.17.3 or later.

## Is CVE-2026-40242 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-40242 exists.

Public exploit code:

- Arcane <= 1.17.2 - Server-Side Request Forgery (nuclei): http/cves/2026/CVE-2026-40242.yaml

## Other vulnerabilities in getarcaneapp arcane

- [CVE-2026-42461](https://insights.sbomify.com/CVE-2026-42461/): Arcane Vulnerable to Unauthenticated Disclosure of Custom Compose Template Content (incl. `.env` secrets) (high 8.7)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-40242 and fix it if it is affected.

What it is: CVE-2026-40242 is a high-severity server-side request forgery vulnerability in getarcaneapp arcane, published on 10 Apr 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-40242 exists.

Affected packages and fixed versions:
- github.com/getarcaneapp/arcane/backend (Go): affected all versions; fixed in 1.17.3
- github.com/getarcaneapp/arcane/backend (Go): affected all versions; fixed in 1.17.3
- github.com/getarcaneapp/arcane/backend (Go): affected all versions; fixed in 1.17.3

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-2026-40242/ (Markdown: https://insights.sbomify.com/CVE-2026-40242/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-40242
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-40242
- OSV: https://osv.dev/vulnerability/CVE-2026-40242

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-40242/
Summaries are generated and may contain mistakes; the official description above is the record.