CVE-2026-27638 is a medium-severity missing authorization vulnerability in @actual-app/sync-server (npm), affecting versions <= 26.2.0. It is fixed in 26.2.1.
In multi-user mode (OpenID), the sync API endpoints (/sync/) don't verify that the authenticated user owns or has access to the file being operated on. Any authenticated user can read, modify, and overwrite any other user's budget files by providing their file ID. Affected Code File: packages/sync-server/src/app-sync.ts The validateSessionMiddleware on line 31 confirms the user is authenticated, but individual endpoints only check that the file exists (via verifyFileExists), never that the requesting user owns or has access to* the file. Compare with POST /sync/delete-user-file (lines 394-430) which correctly checks: This check is missing from all other endpoints. Affected Endpoints GET /sync/download-user-file - download any budget file POST /sync/upload-user-file - overwrite any budget file POST /sync/sync - read/write sync messages of any file POST /sync/user-get-key - read encryption key info POST /sync/user-create-key - change encryption key POST /sync/reset-user-file - reset sync state POST /sync/update-user-filename - rename file GET /sync/get-user-file-info - read file metadata PoC Setup: Two users (Alice, Bob) authenticated via OpenID on the same Actual server. Alice has a budget with fileId abc-123. Bob downloads Alice's budget: Bob reads Alice's file metadata: Bob renames Alice's budget: Bob resets Alice's sync state (destructive): File IDs can be discovered by admin users via GET /sync/list-user-files (admins see all files), through user_access sharing, or by guessing. Impact In multi-user deployments (OpenID mode), any authenticated user can steal other users' complete financial data (transactions, accounts, balances, payees), modify or destroy their budgets, and tamper with encryption keys. This is a personal finance app, so the data is highly sensitive.
The application does not perform an authorization check before performing a sensitive operation. Typical impact: unauthorized access to restricted functionality or data.
npm
@actual-app/sync-server (<= 26.2.0)@actual-app/sync-server → 26.2.1 (npm)Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
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Already deployed Kodem? See CVE-2026-27638 in your environment →Upgrade @actual-app/sync-server to 26.2.1 or later to resolve this vulnerability.
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CVE-2026-27638 is a medium-severity missing authorization vulnerability in @actual-app/sync-server (npm), affecting versions <= 26.2.0. It is fixed in 26.2.1. The application does not perform an authorization check before performing a sensitive operation.
@actual-app/sync-server (npm) versions <= 26.2.0 is affected.
Yes. CVE-2026-27638 is fixed in 26.2.1. Upgrade to this version or later.
Whether CVE-2026-27638 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
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.
Upgrade @actual-app/sync-server to 26.2.1 or later.