livebook: Relative Path Traversal
CVE-2026-66881 is a high-severity relative path traversal vulnerability in livebook from Livebook-dev, with a CVSS 3.1 base score of 8.1 out of 10. It can be exploited remotely over the network by an unauthenticated attacker, but only if a user takes part, for example by opening a link or file. The record lists versions 0.18.7, 0.19.9, 0.18.7-cuda12 as the first without the flaw, so updating livebook to one of those releases or later removes the exposure. There is no confirmed exploitation so far. EPSS estimates a 0.62% chance of exploitation within 30 days, higher than 50% of scored CVEs.
High severity with no evidence of exploitation so far.
What to do
- Update livebook to 0.18.7 or 0.19.9 or 0.18.7-cuda12 or 0.19.9-cuda12, whichever matches your release line, or a later version.
- Read the advisory on cna.erlef.org for workarounds and exact fixed builds.
- Until you can update, restrict network access to the affected service so it is not reachable from untrusted networks.
- Because the attack needs a user to take part, warn users about unexpected links and files related to this product until it is patched.
Affected products and versions
| Vendor | Product | Affected versions | Fixed in |
|---|---|---|---|
| Livebook-dev | livebook | 0.11.0 up to, but not including, 0.18.7; 0.19.0 up to, but not including, 0.19.9; 0.11.0-cuda12 up to, but not including, 0.18.7-cuda12; 0.19.0-cuda12 up to, but not including, 0.19.9-cuda12; c02eb984f80a543c7a52b1d882c76f56aa5be743 and later | 0.18.7, 0.19.9, 0.18.7-cuda12, 0.19.9-cuda12 |
Version data comes from the organisation that assigned the CVE. Confirm against the vendor advisory before deciding you are unaffected.
How the severity score breaks down
- Attack vector
- NetworkCan be exploited remotely over a network, including the internet.
- Attack complexity
- LowNo special conditions are needed; the attack works reliably.
- Privileges required
- NoneNo account or login is needed.
- User interaction
- RequiredA user must take an action such as opening a file or link.
- Scope
- UnchangedImpact stays within the vulnerable component.
- Confidentiality
- NoneNo data is disclosed.
- Integrity
- HighData or code can be modified at will.
- Availability
- HighThe component can be taken down completely.
Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:H/A:H. Scored by NVD.
| Scoring system | Score | Severity | Scored by |
|---|---|---|---|
| CVSS 4.0 | 7.0 | High | CNA |
| CVSS 3.1 | 8.1 | High | NVD |
Official description
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.
Source: the CVE record as published by its numbering authority, via NVD and CVE.org.
The underlying weakness: Relative Path Traversal
The product uses external input to construct a pathname that should be within a restricted directory, but it does not properly neutralize sequences such as.. that can resolve to a location that is outside of that directory.
How developers prevent this class of flaw
- Use an application firewall that can detect attacks against this weakness. It can be beneficial in cases in which the code cannot be fixed (because it is controlled by a third party), as an emergency prevention measure while more comprehensive software assurance measures are applied, or to provide defense in depth.
Timeline
- CVE record published.
- CISA published its SSVC assessment (exploitation: poc, automatable: no, technical impact: partial).
- Record last changed materially (score, affected products, status or references).
References
Advisories
Patches and release notes
- github.com/livebook-dev/livebook/commit/1443dd23df6e7b9203b6797f0695a807aeb81dde
- github.com/livebook-dev/livebook/commit/50f86982ebf36c22abeb379b55ec0f2859c83bb9
- github.com/livebook-dev/livebook/commit/acf4cb8c0c79b89c795b180f061be7de2d8b5aa9
- github.com/livebook-dev/livebook/commit/c02eb984f80a543c7a52b1d882c76f56aa5be743
Third-party and government advisories
- osv.dev/vulnerability/EEF-CVE-2026-66881Third Party Advisory
Other vulnerabilities in livebook
- 8.8 High severity
- 8.8 High severity
- 8.0 High severity
- 9.8 Critical severity
Recent Relative Path Traversal vulnerabilities
- 7.5 High severity
- 8.7 High severity
- 8.1 High severity
- 7.2 High severity
- 7.5 High severity
- 8.0 High severity
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