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

High severity GitHub Reviewed Published Apr 10, 2026 in getarcaneapp/arcane • Updated Apr 10, 2026

Package

gomod github.com/getarcaneapp/arcane/backend (Go)

Affected versions

<= 1.17.2

Patched versions

1.17.3

Description

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 unauthenticated GET request to /api/templates/fetch, passing the target URL as the url query parameter.

image

Impact

  • Unauthenticated port scanning of internal networks
  • Access to internal HTTP services not exposed to the public internet (service discovery endpoints, internal dashboards, Kubernetes API)

References

@kmendell kmendell published to getarcaneapp/arcane Apr 10, 2026
Published to the GitHub Advisory Database Apr 10, 2026
Reviewed Apr 10, 2026
Published by the National Vulnerability Database Apr 10, 2026
Last updated Apr 10, 2026

Severity

High

CVSS overall score

This score calculates overall vulnerability severity from 0 to 10 and is based on the Common Vulnerability Scoring System (CVSS).
/ 10

CVSS v3 base metrics

Attack vector
Network
Attack complexity
Low
Privileges required
None
User interaction
None
Scope
Changed
Confidentiality
Low
Integrity
Low
Availability
None

CVSS v3 base metrics

Attack vector: More severe the more the remote (logically and physically) an attacker can be in order to exploit the vulnerability.
Attack complexity: More severe for the least complex attacks.
Privileges required: More severe if no privileges are required.
User interaction: More severe when no user interaction is required.
Scope: More severe when a scope change occurs, e.g. one vulnerable component impacts resources in components beyond its security scope.
Confidentiality: More severe when loss of data confidentiality is highest, measuring the level of data access available to an unauthorized user.
Integrity: More severe when loss of data integrity is the highest, measuring the consequence of data modification possible by an unauthorized user.
Availability: More severe when the loss of impacted component availability is highest.
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:L/A:N

EPSS score

Exploit Prediction Scoring System (EPSS)

This score estimates the probability of this vulnerability being exploited within the next 30 days. Data provided by FIRST.
(5th percentile)

Weaknesses

Server-Side Request Forgery (SSRF)

The web server receives a URL or similar request from an upstream component and retrieves the contents of this URL, but it does not sufficiently ensure that the request is being sent to the expected destination. Learn more on MITRE.

CVE ID

CVE-2026-40242

GHSA ID

GHSA-ff24-4prj-gpmj

Source code

Credits

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