Docling: `enable_local_fetch` is not enforced in HTML browser-rendering mode

Summary

When the HTML backend renders pages in a headless browser (HTMLBackendOptions(render_page=True)), the enable_local_fetch option is not enforced. A crafted HTML file can embed an arbitrary local file (for example with <iframe src="file:///...">), and that file's contents appear in the page image attached to the returned DoclingDocument.

Details

In render mode, Playwright requests are filtered by HTMLDocumentBackend._get_browser_request_block_reason. In affected versions, this check allowed file: URLs unconditionally, before reading any option. As a result:

• enable_local_fetch=False did not block local file access, and
• even with enable_local_fetch=True, file access was not limited to the source document's directory, unlike the non-render path (ImageResourceLoader), which rejects absolute paths and path traversal.

Versions 2.82.0–2.90.x did no request filtering in render mode at all.

The browser runs with JavaScript disabled (from 2.91.0), so disclosure is passive: only what Chromium renders visibly inside the page viewport ends up in the page image.

Only Path inputs are affected. They are loaded through a file:// URL. Stream inputs are loaded with page.set_content() into an opaque origin, from which Chromium does not load file:// subresources.

Impact

An attacker who can submit HTML for conversion can read any text file the conversion process can read (for example .env files, credential files, or other users' documents on a shared host) by having it rendered into the page image.

Only applications that meet all of these conditions are affected:

• they set HTMLBackendOptions(render_page=True) in Python,
• they have the optional playwright dependency installed, and
• they pass untrusted HTML as a filesystem Path.

The following are not affected: the default configuration (render_page=False), the docling CLI, docling-serve, and the EPUB, Markdown, XBRL and email backends.

Patches

Fixed in 2.118.1 (#3948). In render mode, file: requests are now blocked unless enable_local_fetch=True, and allowed requests are limited to the source document's directory.

Workarounds

If you can't upgrade, don't use render_page=True on untrusted HTML, or pass the input as a stream instead of a Path.

Credits

Reported by @priyankn.