CVE-2026-66881

What it is

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.

At a glance

Exploitability

Can be exploited over the network without logging in, but needs a user to act. High risk of data tampering.

Exploit odds

0.6% chance of exploitation in the next 30 days (EPSS).

Fix

A patch, advisory or fixed version is referenced. Upgrade or apply it.

Timeline

1. 2026-08-05 20:17 UTC PublishedDisclosed publicly on CVE.org and NVD
2. 2026-11-10 18:17 UTC Last updatedMost recent change to the record

Why it ranks here

• Exploited in the wild: no, CISA does not list it.
• Exploit odds: 0.6% in the next 30 days (EPSS).
• Severity: 7.0 HIGH (CVSS).
• Fix: a patch or advisory is linked.

Details

Published

2026-08-05 20:17 UTC

Last modified

2026-11-10 18:17 UTC

Exploit probability

0.6% · EPSS, next 30 days

Weakness

CWE-23

Record status

Modified

Affected

• Livebook < 0.18.7
• Livebook < 0.19.9

Attack profile CVSS 4.0 · 7.0

Attack vector

Network

Complexity

Low

Attack requirements

None

Privileges needed

None

User interaction

Active

Confidentiality

None

Integrity

High

Availability

Low

Is it in your code?

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