Vulnerability in tinacms (CVE-2026-108261)
Summary
Vulnerability in tinacms (CVE-2026-108261). Confidential information can be exposed externally. Exploitable via GET /evil.html. Mitigation: upgrade to 3.14.0 or later.
Original description
The description as published by the source.
Summary
The TinaCMS admin builds its preview `` 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 react-router-dom@6.30.3 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…
Source: GitHub Security Advisories (Global) NVD GitHub Advisory
Auto-generated summary
Assembled by SecPulse from the source data (CVSS, CWE, affected versions) using templates — no AI involved. Check the original description and references below for exact details.
A vulnerability tracked as CVE-2026-108261 has been found in tinacms.
Attackers can target a specific entry point like GET /evil.html over the network to misuse the product.
Confidential information can be exposed externally. CVSS score: 9.3/10.
What to do: upgrade tinacms to 3.14.0 or later.
If unsure, ask your IT team or search "tinacms CVE-2026-108261" on the vendor's site.
CVE-2026-108261 (tinacms) — CWE-346 / CVSS v3 9.3
Attack vector: remote (network-reachable) / unauthenticated
Attack surface: GET /evil.html / GET /exfil / expectedOrigin / postMessage
Patched: 3.14.0 — apply immediately
Plan: 1) Audit SBOM/dependencies, 2) Stage→prod upgrade, 3) Add WAF/proxy monitoring on affected endpoints, 4) Hunt IOCs in logs.
Refs: see the GHSA / vendor advisory / patched release linked on this page.
A vulnerability (CWE-346) exists in tinacms. Attackers reach the vulnerable code path via GET /evil.html without authentication.
Check the vendor advisory for the affected versions of tinacms. Attack surface: GET /evil.html / GET /exfil / expectedOrigin / postMessage.
Severity: Critical (CVSS 9.3/10). Confidential information can be exposed externally.
Update to 3.14.0.
Until the patch is applied: disable the affected feature, apply WAF rules, or restrict access via network ACLs.
Search webserver/proxy logs for unusual GET /evil.html requests with malformed payloads or SQL meta-characters. Run grep -r 'tinacms' . against your dependency files (package-lock.json, requirements.txt, go.sum) to find affected services.
Response actions
Concrete steps and command examples for SOC/SRE teams to execute in order
-
1Identify exposure identify
grep -r 'tinacms' . | grep -v node_modulesリポジトリと本番環境の依存ファイル (package-lock.json / requirements.txt / go.sum / Gemfile.lock 等) で
tinacmsを grep し、稼働しているサービス・バージョンを把握する。 -
2Hunt for indicators of compromise detect
grep 'GET /evil.html' /var/log/nginx/access.log | grep -E '(unusual_payload|sqli_pattern)'アクセスログで
GET /evil.htmlへの異常なリクエスト (不正な認証ヘッダ・SQLメタ文字)を過去 30〜90日分捜索。WAF/SIEM があれば該当パスのアラート発火履歴を確認。 -
3Apply patch patch
Upgrade tinacms to 3.14.0ステージング環境で 3.14.0 に上げて回帰テスト → 本番反映。回帰テストはアプリの主要ハッピーパスと、Step 2 で見つけた異常検知の続報チェックを含めること。
-
4Post-deployment verification verify
Replay attack against GET /evil.html on staging to confirm patch closes the vectorパッチ適用後、ステージングで PoC または同等の悪用パターンを再現して脆弱性が閉じたことを確認。本番では Step 2 と同じログクエリでアラート再発が無いか継続監視。