CVE-2026-40242

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.

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

Untrusted input controls the target URL of a server-initiated request, which may reach internal services not otherwise accessible from outside. Typical impact: access to internal metadata services, internal APIs, or cloud credentials.

CVE-2026-40242 has a CVSS score of 7.2 (High). The vector is network-reachable, no privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (1.17.3); upgrading removes the vulnerable code path.

Kodem intelligence

1. What is CVE-2026-40242? CVE-2026-40242 is a high-severity server-side request forgery (SSRF) vulnerability in github.com/getarcaneapp/arcane/backend (go), affecting versions <= 1.17.2. It is fixed in 1.17.3. Untrusted input controls the target URL of a server-initiated request, which may reach internal services not otherwise accessible from outside.
2. How severe is CVE-2026-40242? CVE-2026-40242 has a CVSS score of 7.2 (High). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
3. Which versions of github.com/getarcaneapp/arcane/backend are affected by CVE-2026-40242? github.com/getarcaneapp/arcane/backend (go) versions <= 1.17.2 is affected.
4. Is there a fix for CVE-2026-40242? Yes. CVE-2026-40242 is fixed in 1.17.3. Upgrade to this version or later.
5. Is CVE-2026-40242 exploitable, and should I be worried? Whether CVE-2026-40242 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
6. What actually determines whether CVE-2026-40242 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
7. How do I fix CVE-2026-40242? Upgrade github.com/getarcaneapp/arcane/backend to 1.17.3 or later.