# CVE-2026-66881: Relative Path Traversal vulnerability in livebook-dev livebook allows an attacker-authored notebook to write a file…

Source: https://junglewise.ai/threats/cve-2026-66881-relative-path-traversal-vulnerability-in-livebook-dev-livebook  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-08-05  
License: CC BY 4.0 with a link back

CVE-2026-66881 · Severity: high · CVSS 8.1 · Published 2026-08-05

Relative Path Traversal vulnerability in livebook-dev livebook allows an attacker-authored notebook to write a file with attacker-controlled content to an arbitrary path.

A .livemd notebook can declare file_entries metadata, each entry carrying a name. Every path that creates a file entry through the user interface validates that name with Livebook.Notebook.validate_file_entry_name/2, which requires a flat filename of alphanumerics, dashes, underscores and dots, ending in an extension. The import path does not: Livebook.LiveMarkdown.Import.file_entry_metadata_to_attrs/1 in lib/livebook/live_markdown/import.ex takes the name verbatim from the notebook source.

For a URL-type file entry, Livebook.Session.file_entry_cache_file/2 in lib/livebook/session.ex resolves that name beneath the session's temporary directory without checking that the result stays inside it, and Livebook.FileSystem.Utils.resolve_unix_like_path/2 collapses parent-directory segments while clamping only at the filesystem root. When the entry's content is requested and no cached copy exists, Livebook fetches the entry's URL and writes the response body to the resolved path, creating parent directories as needed. The attacker therefore controls both the destination and the contents of the written file, which may land anywhere the Livebook process can write. The same missing containment check is present in Livebook.Session.to_attachment_file_entry/2.

A victim who opens an attacker-supplied notebook and causes the entry to be fetched triggers the write within their own authenticated session; the attacker needs no account on the target instance. URL-type entries are also not placed under notebook stamping quarantine on import, so no warning is shown.

This issue affects livebook: from 0.11.0 before 0.18.7 and from 0.19.0 before 0.19.9.

Technologies: [Livebook](https://junglewise.ai/threats/technologies/livebook). Vendors: [Livebook](https://junglewise.ai/threats/vendors/livebook).

## Quick answers

**Is CVE-2026-66881 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-66881 being exploited in the wild.

**How severe is CVE-2026-66881?** High severity, with a CVSS score of 8.1, published 5 August 2026.

**Which products and versions are affected?** Livebook. The advisory does not name versions.

**Is there a fix for CVE-2026-66881?** No fixed version is recorded yet. Check the vendor's advisory in the references below. If you run it, Junglewise drafts a mitigation that fits your setup and applies it once you approve, with senior security engineers behind it.

**Am I affected by CVE-2026-66881?** Check whether you run Livebook. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## Affected products

- Livebook

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