TinaCMS admin preview iframe loads an attacker-controlled origin from the URL fragment

Exploitation

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

CVSS

9.3 · CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:H/A:N

EPSS

• CVE-2026-108261: 0.20% estimated exploitation activity in the next 30 days; percentile 9.49 (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 The TinaCMS admin builds its preview <iframe src from the /~/ hash-router splat without checking that the value stays same-origin. A fragment with a doubled slash (#/~//attacker.example/p) becomes the protocol-relative URL //attacker.example/p, so the admin frames an external site. That same unvalidated string derives expectedOrigin, the only trust anchor for the admin↔preview postMessage channel, so the attacker's frame is treated as trusted: it can submit any GraphQL operation, which the admin executes with the signed-in editor's token and posts back to the attacker's origin. One link, opened by a logged-in editor, gives an unauthenticated remote attacker arbitrary read and write access to the site's content API as that editor. Details Root cause — the router splat becomes the frame source with no same-origin check: The leading / is meant to force a relative path, but react-router-dom@6.30.3 returns the splat with its own leading slash for /~//x, producing //x. The iframe…

Published by the source

9 Oct 2026, 20:56 UTC

Last modified by the source

9 Oct 2026, 21:15 UTC

Source last checked

26 Oct 2026, 13:07 UTC

1. Revision 3 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-x34j-47hf-4xg7

2. Revision 2 · amended · 24 Oct 2026

   Amended from osv record GHSA-x34j-47hf-4xg7

3. Revision 1 · created · 23 Oct 2026

   Published from ghsa record GHSA-x34j-47hf-4xg7

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# Patch Next advisory brief: CVE-2026-108261

Advisory: TinaCMS admin preview iframe loads an attacker-controlled origin from the URL fragment
IDs: CVE-2026-108261, GHSA-x34j-47hf-4xg7
Record: https://patchnext.com/advisories/cve-2026-108261 (revision 3, source checked 26 Oct 2026, 13:07 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Critical (CVSS 9.3)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: tinacms 3.14.0; @tinacms/app 2.5.14. A vendor fix does not mean a deployment is fixed.

## Affected components
- npm tinacms: affected <= 3.13.0; fixed in 3.14.0
- npm @tinacms/app: affected <= 2.5.13; fixed in 2.5.14

## Suggested inspection (read-only)
- `npm ls tinacms --all`: lists every installed copy and version, including transitive ones. Run in the project root after `npm ci`.
- `npm ls @tinacms/app --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 tinacms, @tinacms/app.
- 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-x34j-47hf-4xg7 (GitHub-reviewed advisory GHSA-x34j-47hf-4xg7 lists affected ranges: npm tinacms >=0 =0 <=2.5.13)
- Verified: https://osv.dev/vulnerability/GHSA-x34j-47hf-4xg7 (OSV record GHSA-x34j-47hf-4xg7 lists affected ranges: npm tinacms >=0 =0 <2.5.14 (fixed))

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