An unknown threat actor has been observed using a large language model (LLM) agent to conduct post-compromise actions after obtaining initial access following the exploitation of a publicly-accessible Marimo network using a recently disclosed vulnerability. "The attacker compromised an internet-reachable Marimo notebook via CVE-2026-39987, extracted two cloud credentials from the compromised host, replayed them through a fanned-out egress pool to retrieve an SSH private key from AWS Secrets Manager, and used that key to drive eight short SSH sessions against a downstream SSH bastion server," Sysdig said. "The bastion phase exfiltrated the schema and full contents of an internal PostgreSQL database in under two minutes." CVE-2026-39987 refers to a critical pre-authenticated remote code execution vulnerability impacting all versions of Marimo prior to and including 0.20.4. It allows an unauthenticated attacker to execute arbitrary system commands. The issue was addressed in version 0.23.0, released last month. The security defect has since come under active exploitation, with threat actors using it to initiate manual reconnaissance against honeypot systems and attempt to harvest sensitive data. The latest activity documented by Sysdig sticks to the same pattern, the primary difference being that an LLM agent was used to drive the post-exploitation activity. The incident, per the cloud security firm, was recorded on May 10, 2026, with the attacker gathering credentials from the environment and then using the harvested AWS access key to perform API calls against AWS Secrets Manager and retrieve an SSH private key. Minutes later, the threat actor is said to have carried out the first SSH authentication on the SSH bastion server using the retrieved key, followed by launching eight parallel SSH sessions against the downstream server to siphon an internal PostgreSQL database. The end-to-end attack chain lasted a little over an hour. Sysdig said it uncovered four indi