CVE-2026-66881
CVE-2026-66881 is a CWE-23 vulnerability. O3 Security confirms whether CVE-2026-66881 is actually reachable in your code before you act, and blocks exploitation at runtime until you patch.
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…
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.
Detection & mitigation playbook
VulnerabilityDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for the affected component. O3's reachability analysis confirms whether the vulnerable code path is actually invoked in your application, so you act on real exposure instead of every transitive match.
Remediation status
No patched version of the affected component has shipped for CVE-2026-66881 yet. Where your build allows, override or pin the dependency away from the vulnerable range, and apply any maintainer-recommended mitigation.
Mitigate without a patch
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 pinpoints whether CVE-2026-66881 is reachable in your code and exactly where to fix it, then blocks exploitation in production at runtime until the patched version is deployed.
Tailored to CVE-2026-66881. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is CVE-2026-66881 in your dependencies?
O3 detects CVE-2026-66881 across dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.