@tinacms/graphql's Media Endpoints Can Escape the Media Root via Symlinks or Junctions

## Summary `@tinacms/cli` recently added lexical path-traversal checks to the dev media routes, but the implementation still validates only the path string and does not resolve symlink or junction targets. If a link already exists under the media root, Tina accepts a path like `pivot/written-from-media.txt` as "inside" the media directory and then performs real filesystem operations through that link target. This allows out-of-root media listing and write access, and the same root cause also affects delete. ## Details The dev media handlers validate user-controlled paths with: ```ts function resolveWithinBase(userPath: string, baseDir: string): string { const resolvedBase = path.resolve(baseDir); const resolved = path.resolve(path.join(baseDir, userPath)); if (resolved === resolvedBase) { return resolvedBase; } if (resolved.startsWith(resolvedBase + path.sep)) { return resolved; } throw new PathTraversalError(userPath); } function resolveStrictlyWithinBase(userPath: string, baseDir: string): string { const resolvedBase = path.resolve(baseDir) + path.sep; const resolved = path.resolve(path.join(baseDir, userPath)); if (!resolved.startsWith(resolvedBase)) { throw new PathTraversalError(userPath); } return resolved; } ``` But the validated path is then used directly for real filesystem access: ```ts filesStr = await fs.readdir(validatedPath); ... await fs.ensureDir(path.dirname(saveTo)); file.pipe(fs.createWriteStream(saveTo)); ... await fs.remove(file); ``` This does not account for symlinks/junctions already present below the media root. A path such as `pivot/secret.txt` can be lexically inside the media directory while the filesystem target is outside it. ## Local Reproduction I verified this locally with a real junction on Windows. Test layout: - media root: `D:\bugcrowd\tinacms\temp\junction-repro4\public\uploads` - junction under media root: `public\uploads\pivot -> D:\bugcrowd\tinacms\temp\junction-repro4\outside` - file outside the media root: `outside\secret.txt` Tina's current media-path validation logic was applied and used to perform the same list/write operations the route handlers use. Observed result: ```json { "media": { "base": "D:\\bugcrowd\\tinacms\\temp\\junction-repro4\\public\\uploads", "resolvedListPath": "D:\\bugcrowd\\tinacms\\temp\\junction-repro4\\public\\uploads\\pivot", "listedEntries": [ "secret.txt" ], "resolvedWritePath": "D:\\bugcrowd\\tinacms\\temp\\junction-repro4\\public\\uploads\\pivot\\written-from-media.txt", "outsideWriteExists": true, "outsideWriteContents": "MEDIA_ESCAPE" } } ``` This shows the problem clearly: - the path validator accepted `pivot` - listing revealed a file from outside the media root - writing to `pivot/written-from-media.txt` created `outside\written-from-media.txt` The delete path uses the same flawed containment model and should be hardened at the same time. ## Impact - **Out-of-root file listing** via `/media/list/...` - **Out-of-root file write** via `/media/upload/...` - **Likely out-of-root file delete** via `/media/...` `DELETE`, using the same path-validation gap - **Bypass of the recent path traversal hardening** for any deployment whose media tree contains a link to another location This is especially relevant in development and self-hosted workflows where the media directory may contain symlinks or junctions intentionally or via repository content. ## Recommended Fix Harden media path validation with canonical filesystem checks: 1. resolve the real base path with `fs.realpath()` 2. resolve the real target path, or for writes the nearest existing parent 3. compare canonical paths rather than lexical strings 4. reject any operation that traverses through a symlink/junction to leave the real media root `path.resolve(...).startsWith(...)` is not sufficient for filesystem security on linked paths. ## Resources - `packages/@tinacms/cli/src/next/commands/dev-command/server/media.ts` - `packages/@tinacms/cli/src/server/models/media.ts` - `packages/@tinacms/cli/src/utils/path.ts`