Arcane has Unauthenticated SSRF with Conditional Response Reflection in Template Fetch Endpoint

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS

7.2 · CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:L/A:N

EPSS

• CVE-2026-40242: 0.62% estimated exploitation activity in the next 30 days; percentile 49.81 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

Summary 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. Details - No allowlist or denylist of destination hosts/CIDRs - No requirement for the caller to be authenticated Response handling produces four distinct outcomes observable by the caller: - Valid JSON targets return a fully reflected response body if the returned fields fit the expected internal struct - Non-JSON HTTP 200 responses produce an error leaking the first byte of the response ("Invalid JSON response: invalid character '<'...") - Non-200 responses leak the HTTP status code - TCP-level failures distinguish between closed ports ("connection refused") and filtered ones ("i/o timeout") PoC Send an…

Published by the source

10 Apr 2026, 20:59 UTC

Last modified by the source

10 Apr 2026, 21:37 UTC

Source last checked

26 Oct 2026, 15:19 UTC

1. Revision 1 · created · 26 Oct 2026

   Published from ghsa record GHSA-ff24-4prj-gpmj

Preview the exact text before you copy it. Commands are read-only suggestions; review them before running anything.

# Patch Next advisory brief: CVE-2026-40242

Advisory: Arcane has Unauthenticated SSRF with Conditional Response Reflection in Template Fetch Endpoint
IDs: CVE-2026-40242, GHSA-ff24-4prj-gpmj
Record: https://patchnext.com/advisories/cve-2026-40242 (revision 1, source checked 26 Oct 2026, 15:19 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: High (CVSS 7.2)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: github.com/getarcaneapp/arcane/backend 1.17.3. A vendor fix does not mean a deployment is fixed.

## Affected components
- Go github.com/getarcaneapp/arcane/backend: affected <= 1.17.2; fixed in 1.17.3

## Suggested inspection (read-only)
- Go github.com/getarcaneapp/arcane/backend: check the installed version with your package manager.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on github.com/getarcaneapp/arcane/backend.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://github.com/advisories/GHSA-ff24-4prj-gpmj (GitHub-reviewed advisory GHSA-ff24-4prj-gpmj lists affected ranges: Go github.com/getarcaneapp/arcane/backend >=0 <=1.17.2)

Commands are suggestions: review each one before running it.