CVE-2026-57449: Actual Sync Server: CORS Proxy GitHub API Allowlist Prefix Bypass Leaks Private Repositories Through the Server GitHub Token

Actual Sync Server’s CORS proxy is intended to let authenticated users fetch resources only from repositories listed in the official plugin allowlist. When ACTUAL_GITHUB_TOKEN is configured, the proxy automatically attaches the server’s GitHub token to GitHub requests.

The GitHub API allowlist check uses a raw startsWith() prefix test for /repos/{owner}/{repo} without requiring a path boundary after the repository name. If an allowlisted public plugin repository is https://github.com/acme/plugin, the proxy also accepts GitHub API URLs such as:

https://api.github.com/repos/acme/plugin-private/contents/.env
https://api.github.com/repos/acme/plugin-secrets/actions/secrets
https://api.github.com/repos/acme/plugin-internal/releases

Those URLs are outside the allowlisted repository but still pass because their API path starts with /repos/acme/plugin. The proxy then forwards the request with the server’s ACTUAL_GITHUB_TOKEN, allowing any authenticated Actual user to read private GitHub resources reachable by that token.