SiYuan versions before v3.7.4 contain a missing authorization vulnerability in the /api/ref/refreshBacklink endpoint that allows anonymous readers to trigger persistent server-side writes. Attackers can invoke the endpoint with an attacker-controlled block ID to flush transaction queues, scan all references globally, and enqueue database writes, bypassing read-only protections and enabling resource amplification attacks.

Affected: Go: github.com/siyuan-note/siyuan/kernel

**CVE:** This vulnerability corresponds to [CVE-2026-72812](https://nvd.nist.gov/vuln/detail/CVE-2026-72812).

### Summary

The `/api/ref/refreshBacklink` endpoint is gated by `CheckAuth` only. Unlike its mutating siblings, it carries no `CheckAdminRole`, no `CheckReadonly`, and no inline reader-role guard so it falls through all three authorization mechanisms the codebase uses to protect write operations. A publish `RoleReader` or the anonymous account when `Publish.Auth.Enable` is `false` can invoke it, forcing the server to flush its pending write-transaction queue, scan all references globally, load and parse referencing trees from disk, and enqueue database writes. This violates the read-only invariant (it writes even in a globally read-only workspace), provides an unauthenticated resource-amplification/DoS primitive, and applies no per-object access check to the caller-supplied ID.

### Details

**Route / auth tier.** `router.go`: `Handle("POST", "/api/ref/refreshBacklink", model.CheckAuth, refreshBacklink)`, `CheckAuth` only. `CheckAuth` admits `RoleReader`; the publish proxy forwards port-6808 traffic with a Reader JWT (anonymous account when publish auth is disabled). Anonymous/reader reachable.

**Guard fall-through.** SiYuan protects write handlers with one of three mechanisms: route-level `CheckAdminRole` (AV/riff/repo/sync/setting/snippet/notebook mutations), route-level `CheckReadonly` (filetree/block/attr/tag mutations), or an inline `IsReadOnlyRoleContext` ch…