CVE-2026-108261

Tina is a headless content management system. Prior to tinacms 3.14.0 and @tinacms/app 2.5.14, the /~/* admin preview route in packages/tinacms/src/admin/index.tsx can turn an attacker-controlled hash-router splat into an off-origin iframe URL through packages/@tinacms/app/src/preview.tsx, while packages/@tinacms/app/src/lib/preview-origin.ts derives expectedOrigin from that same URL for the GraphQL message channel in packages/@tinacms/app/src/lib/graphql-reducer.ts. An unauthenticated attacker can send a crafted link to a signed-in editor, cause the admin to frame an attacker origin, and have that frame treated as the trusted preview. The attacker-controlled frame can submit GraphQL reads or mutations that the admin executes with the editor credentials, exposing or modifying protected content. This issue is fixed in tinacms 3.14.0 and @tinacms/app 2.5.14.

Tina is a headless content management system. Prior to tinacms 3.14.0 and @tinacms/app 2.5.14, the /~/* admin preview route in packages/tinacms/src/admin/index.tsx can turn an attacker-controlled hash-router splat into an off-origin iframe URL through packages/@tinacms/app/src/preview.tsx, while packages/@tinacms/app/src/lib/preview-origin.ts derives expectedOrigin from that same URL for the GraphQL message channel in packages/@tinacms/app/src/lib/graphql-reducer.ts. An unauthenticated attacker can send a crafted link to a signed-in editor, cause the admin to frame an attacker origin, and have that frame treated as the trusted preview. The attacker-controlled frame can submit GraphQL reads or mutations that the admin executes with the editor credentials, exposing or modifying protected content. This issue is fixed in tinacms 3.14.0 and @tinacms/app 2.5.14.

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:

packages/tinacms/src/admin/index.tsx:16     HashRouter as Router,
packages/tinacms/src/admin/index.tsx:329      path='/~/*'
packages/tinacms/src/admin/index.tsx:173    const [url, setURL] = React.useState(`/${params['*']}`);
packages/tinacms/src/admin/index.tsx:176    const paramURL = `/${params['*']}`;
packages/@tinacms/app/src/preview.tsx:24        src={props.url}

The leading / is meant to force a relative path, but [email protected] returns the splat with its own leading slash for /~//x, producing //x. The iframe has no sandbox attribute and the admin bundle ships no CSP.

The trust anchor is then computed from that same value:

packages/@tinacms/app/src/lib/graphql-reducer.ts:209-212   getExpectedPreviewOrigin(url)
packages/@tinacms/app/src/lib/preview-origin.ts:22           return new URL(url, baseOrigin || undefined).origin;
packages/@tinacms/app/src/lib/preview-origin.ts:43-46        event.origin !== expectedOrigin -> reject

Both guards pass for the attacker: event.origin is expectedOrigin, and event.source is the frame the admin itself loaded.

PreviewInner's URL-correction poll (packages/tinacms/src/admin/index.tsx:189-200) does not recover the frame: reading ref.current.contentWindow.location.href across origins throws an uncaught SecurityError, so setReportedURL never fires and no corrective navigate() happens. The PoC below includes that effect verbatim and the attack still completes.

Sink — the attacker's GraphQL string reaches the authenticated client, and the result goes back to the attacker:

packages/@tinacms/app/src/lib/graphql-reducer.ts:613-624   'open' handler; zod validates types only, not query content
packages/@tinacms/app/src/lib/graphql-reducer.ts:973-978   cms.api.tina.request(expandedQuery, { variables })
packages/@tinacms/app/src/lib/graphql-reducer.ts:497-505   postMessageToPreview(..., expectedOrigin)

expandQuery (packages/@tinacms/app/src/lib/expand-query.ts:3-18) is operation-agnostic, so mutations pass through unchanged.

Default-enabled: packages/@tinacms/app/src/App.tsx:70 always passes preview={Preview}, and packages/tinacms/src/admin/index.tsx:327 registers /~/* whenever preview is truthy — so the route exists in every tinacms build output and in tinacms dev.

Incomplete-fix note: [email protected] / @tinacms/[email protected] (PR #7056, c491fc5) added the sender-side origin check, but never validated the URL that check compares against.

Affected-range basis, stated plainly: I tested only [email protected] / @tinacms/[email protected] (commit 0d38acf). The ranges below are given as <= because the vulnerable lines are byte-identical across every commit available to me — a 123-commit shallow clone, earliest 8a86ffa (2026-06-26), which predates the 3.9.3 hardening release — but I did not fetch tags or test earlier releases, so the true lower bound is undetermined. Please narrow it from your own history.

Suggested fix: normalise the splat to a same-origin path before it becomes url (reject a leading / or \), and have getExpectedPreviewOrigin…

Tina is a headless content management system. Prior to tinacms 3.14.0 and @tinacms/app 2.5.14, the /~/* admin preview route in packages/tinacms/src/admin/index.tsx can turn an attacker-controlled hash-router splat into an off-origin iframe URL through packages/@tinacms/app/src/preview.tsx, while packages/@tinacms/app/src/lib/preview-origin.ts derives expectedOrigin from that same URL for the GraphQL message channel in packages/@tinacms/app/src/lib/graphql-reducer.ts. An unauthenticated attacker can send a crafted link to a signed-in editor, cause the admin to frame an attacker origin, and have that frame treated as the trusted preview. The attacker-controlled frame can submit GraphQL reads or mutations that the admin executes with the editor credentials, exposing or modifying protected content. This issue is fixed in tinacms 3.14.0 and @tinacms/app 2.5.14.

Tina is a headless content management system. Prior to tinacms 3.14.0 and @tinacms/app 2.5.14, the /~/* admin preview route in packages/tinacms/src/admin/index.tsx can turn an attacker-controlled hash-router splat into an off-origin iframe URL through packages/@tinacms/app/src/preview.tsx, while packages/@tinacms/app/src/lib/preview-origin.ts derives expectedOrigin from that same URL for the GraphQL message channel in packages/@tinacms/app/src/lib/graphql-reducer.ts. An unauthenticated attacker can send a crafted link to a signed-in editor, cause the admin to frame an attacker origin, and have that frame treated as the trusted preview. The attacker-controlled frame can submit GraphQL reads or mutations that the admin executes with the editor credentials, exposing or modifying protected content. This issue is fixed in tinacms 3.14.0 and @tinacms/app 2.5.14.

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:

packages/tinacms/src/admin/index.tsx:16     HashRouter as Router,
packages/tinacms/src/admin/index.tsx:329      path='/~/*'
packages/tinacms/src/admin/index.tsx:173    const [url, setURL] = React.useState(`/${params['*']}`);
packages/tinacms/src/admin/index.tsx:176    const paramURL = `/${params['*']}`;
packages/@tinacms/app/src/preview.tsx:24        src={props.url}

The leading / is meant to force a relative path, but [email protected] returns the splat with its own leading slash for /~//x, producing //x. The iframe has no sandbox attribute and the admin bundle ships no CSP.

The trust anchor is then computed from that same value:

packages/@tinacms/app/src/lib/graphql-reducer.ts:209-212   getExpectedPreviewOrigin(url)
packages/@tinacms/app/src/lib/preview-origin.ts:22           return new URL(url, baseOrigin || undefined).origin;
packages/@tinacms/app/src/lib/preview-origin.ts:43-46        event.origin !== expectedOrigin -> reject

Both guards pass for the attacker: event.origin is expectedOrigin, and event.source is the frame the admin itself loaded.

PreviewInner's URL-correction poll (packages/tinacms/src/admin/index.tsx:189-200) does not recover the frame: reading ref.current.contentWindow.location.href across origins throws an uncaught SecurityError, so setReportedURL never fires and no corrective navigate() happens. The PoC below includes that effect verbatim and the attack still completes.

Sink — the attacker's GraphQL string reaches the authenticated client, and the result goes back to the attacker:

packages/@tinacms/app/src/lib/graphql-reducer.ts:613-624   'open' handler; zod validates types only, not query content
packages/@tinacms/app/src/lib/graphql-reducer.ts:973-978   cms.api.tina.request(expandedQuery, { variables })
packages/@tinacms/app/src/lib/graphql-reducer.ts:497-505   postMessageToPreview(..., expectedOrigin)

expandQuery (packages/@tinacms/app/src/lib/expand-query.ts:3-18) is operation-agnostic, so mutations pass through unchanged.

Default-enabled: packages/@tinacms/app/src/App.tsx:70 always passes preview={Preview}, and packages/tinacms/src/admin/index.tsx:327 registers /~/* whenever preview is truthy — so the route exists in every tinacms build output and in tinacms dev.

Incomplete-fix note: [email protected] / @tinacms/[email protected] (PR #7056, c491fc5) added the sender-side origin check, but never validated the URL that check compares against.

Affected-range basis, stated plainly: I tested only [email protected] / @tinacms/[email protected] (commit 0d38acf). The ranges below are given as <= because the vulnerable lines are byte-identical across every commit available to me — a 123-commit shallow clone, earliest 8a86ffa (2026-06-26), which predates the 3.9.3 hardening release — but I did not fetch tags or test earlier releases, so the true lower bound is undetermined. Please narrow it from your own history.

Suggested fix: normalise the splat to a same-origin path before it becomes url (reject a leading / or \), and have getExpectedPreviewOrigin…