CVE-2026-66881 livebook-dev CVE debrief

Who should care

Livebook users, administrators of Livebook instances, security teams responsible for monitoring and patching vulnerabilities in development tools, and operators of affected platforms should be aware of the potential risks associated with CVE-2026-66881. These stakeholders should prioritize updating to a version that addresses this vulnerability to prevent potential arbitrary file writes. They should also review compensating controls for exposed systems while remediation is scheduled and verified, and track exceptions, retest remediated assets, and close the item only after evidence is documented. Additionally, they should check relevant monitoring, detection, and logs for exposed assets that need extra review and implement additional security measures to restrict file system access for Livebook processes if necessary. Vulnerability management and security teams should ensure that affected product deployments are identified in managed environments and assign an owner for follow-up. They should also plan vendor-supported updates or mitigations through normal change control where exposure is confirmed and review the supplied official advisory or CVE record to validate affected scope, severity, and vendor guidance. Asset inventory management should be updated to reflect the presence of affected Livebook instances, and rollback/change windows should be considered for remediation efforts. Source tracking should be implemented to monitor for potential exploitation attempts. Monitoring and detection capabilities should be reviewed to ensure they can identify suspicious activity related to this vulnerability. Compensating controls, such as restricting access to Livebook instances to trusted users and implementing additional security measures to restrict file system access for Livebook processes, should be considered while remediation is scheduled and verified. The goal is to minimize the risk of arbitrary file writes and ensure the security of Livebook instances and their users. By taking these steps, stakeholders can reduce the likelihood of successful exploitation and protect their systems from potential attacks. Furthermore, they should consider the operational impact

Technical summary

The CVE-2026-66881 vulnerability in livebook-dev livebook allows an attacker-authored notebook to write files with attacker-controlled content to arbitrary paths due to a Relative Path Traversal issue. The vulnerability arises from insufficient containment checks when resolving file entry names for URL-type entries in .livemd notebooks. This affects livebook versions from 0.11.0 before 0.18.7 and from 0.19.0 before 0.19.9.

Defensive priority

Livebook users should prioritize updating to a version that addresses this vulnerability to prevent potential arbitrary file writes.

Recommended defensive actions

• Update livebook to version 0.18.7 or later, or 0.19.9 or later.
• Restrict access to Livebook instances to trusted users.
• Monitor Livebook logs for suspicious file writes.
• Implement additional security measures to restrict file system access for Livebook processes.
• Confirm whether affected product deployments exist in managed environments and assign an owner for follow-up.
• Review the supplied official advisory or CVE record to validate affected scope, severity, and vendor guidance.
• Plan vendor-supported updates or mitigations through normal change control where exposure is confirmed.

Evidence notes

The CVE-2026-66881 issue arises from a Relative Path Traversal vulnerability in livebook-dev livebook, allowing an attacker-authored notebook to write files with attacker-controlled content to arbitrary paths. A .livemd notebook can declare file_entries metadata, and for URL-type entries, Livebook resolves the name beneath the session's temporary directory without proper containment checks. This allows an attacker to control both the destination and contents of the written file, potentially landing anywhere the Livebook process can write. The issue affects livebook versions from 0.11.0 before 0.18.7 and from 0.19.0 before 0.19.9.

Official resources