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

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS 4.0

7.1 · CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N · score source

EPSS

• CVE-2026-57449: 0.26% estimated exploitation activity in the next 30 days; percentile 17.51 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

Summary Actual Sync Server's CORS proxy is intended to let authenticated users fetch resources only from repositories listed in the official plugin allowlist. When ACTUALGITHUBTOKEN 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: 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 ACTUALGITHUBTOKEN, allowing any authenticated Actual user to read private GitHub resources reachable by that token. Affected Endpoint - GET /cors-proxy?url=... This endpoint is mounted only when: Source: packages/sync-server/src/app.ts:68-70 Details The CORS proxy is…

Published by the source

7 Oct 2026, 14:00 UTC

Last modified by the source

7 Oct 2026, 14:16 UTC

Source last checked

26 Oct 2026, 13:06 UTC

1. Revision 4 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-m62c-5q34-f3cf

2. Revision 3 · amended · 24 Oct 2026

   Reviewed OSV alias/range/CVSS4 correction; package source scopes and original publication preserved. No customer finding resolved.

3. Revision 2 · amended · 24 Oct 2026

   Amended from osv record GHSA-m62c-5q34-f3cf

4. Revision 1 · created · 23 Oct 2026

   Published from ghsa record GHSA-m62c-5q34-f3cf

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# Patch Next advisory brief: CVE-2026-57449

Advisory: Actual Sync Server: CORS Proxy GitHub API Allowlist Prefix Bypass Leaks Private Repositories Through the Server GitHub Token
IDs: CVE-2026-57449, GHSA-m62c-5q34-f3cf
Record: https://patchnext.com/advisories/cve-2026-57449 (revision 4, source checked 26 Oct 2026, 13:06 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: High (CVSS 7.1)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: @actual-app/sync-server 26.7.0. A vendor fix does not mean a deployment is fixed.

## Affected components
- npm @actual-app/sync-server: affected <= 26.6.0; fixed in 26.7.0

## Suggested inspection (read-only)
- `npm ls @actual-app/sync-server --all`: lists every installed copy and version, including transitive ones. Run in the project root after `npm ci`.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on @actual-app/sync-server.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://github.com/advisories/GHSA-m62c-5q34-f3cf (GitHub-reviewed advisory GHSA-m62c-5q34-f3cf lists affected ranges: npm @actual-app/sync-server >=0 <=26.6.0)
- Verified: https://osv.dev/vulnerability/GHSA-m62c-5q34-f3cf (OSV record GHSA-m62c-5q34-f3cf lists affected ranges: npm @actual-app/sync-server >=0 <26.7.0 (fixed))

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