PatchSiren cyber security CVE debrief
CVE-2026-42461 Unknown Vendor CVE debrief
CVE-2026-42461 describes a backend authorization gap in Arcane's template APIs. Before version 1.18.0, four GET endpoints under /api/templates* were registered without a Security requirement, so an unauthenticated network client could list and read the full Compose YAML and .env content for every custom template stored in an Arcane instance. The issue was patched in Arcane 1.18.0.
- Vendor
- Unknown Vendor
- Product
- Unknown
- CVSS
- HIGH 8.7
- CISA KEV
- Not listed in stored evidence
- Original CVE published
- 2026-05-09
- Original CVE updated
- 2026-05-09
- Advisory published
- 2026-05-09
- Advisory updated
- 2026-05-09
Who should care
Operators of Arcane instances, especially any deployment that uses the "Save as Template" workflow and stores real environment values in templates. This is most urgent for internet-accessible or multi-user instances because the flaw allows unauthenticated reading of template contents.
Technical summary
The CVE record and GitHub advisory state that four GET routes under /api/templates* lacked backend authorization, while POST/PUT/DELETE on the same template paths required a Bearer or API key. The frontend also treats /customize/templates/* as protected, which supports the conclusion that the issue is an unintended backend authorization bypass rather than an intentionally public read-only feature. In practice, the exposed template data can include Compose YAML plus verbatim .env content saved from project or swarm-stack templates.
Defensive priority
High and urgent for any exposed Arcane deployment. Upgrade to version 1.18.0 as soon as possible, and treat this as a secrets-exposure issue rather than a low-impact information disclosure if templates may contain credentials or API keys.
Recommended defensive actions
- Upgrade Arcane to version 1.18.0 or later immediately.
- Restrict network access to Arcane until patching is complete, especially for instances reachable from untrusted networks.
- Review whether custom templates contain secrets or sensitive environment variables, and rotate any credentials that may have been stored there.
- Audit access logs for requests to /api/templates* prior to patching if logs are available.
- Verify that all template-management routes enforce the intended authentication and authorization controls after upgrading.
Evidence notes
The supplied CVE description states that unauthenticated GET endpoints under /api/templates* exposed template Compose YAML and .env content, and that the issue was fixed in Arcane 1.18.0. The NVD record points to the Arcane v1.18.0 release and the GitHub security advisory as supporting references. The record also lists CWE-862, aligning with missing authorization.
Official resources
According to the CVE record, the issue was published on 2026-05-09 and patched in Arcane version 1.18.0. No exploit code or exploit chain details are included here.