Malicious “Claude Code” Browser Extension Deploys Persistent SSH Backdoor on Victims’ Machines
What Happened — Microsoft’s threat‑research team discovered a Chrome/Edge extension masquerading as the AI‑assistant “Claude Code.” The extension, once installed, silently drops an SSH private key into the user’s .ssh directory and creates a scheduled task that re‑establishes the key on reboot, giving an attacker persistent, password‑less SSH access to the host. The backdoor communicates over port 22, evading typical web‑proxy controls, and can be used to exfiltrate files or execute arbitrary commands. Microsoft identified the campaign through telemetry from its Defender for Endpoint product and shared indicators of compromise, detection guidance, and remediation steps.
Why It Matters for Trust & Control Assurance — The incident highlights the need for strong identity‑and‑access controls around privileged credentials and continuous monitoring of unauthorized SSH activity.
Who Is Affected — Software‑as‑a‑Service providers, development teams, and any organization that allows employees to install browser extensions on corporate workstations.
Recommended Actions –
- Inventory and block unauthorized browser extensions via endpoint policy.
- Enforce MFA and just‑in‑time provisioning for privileged SSH keys; rotate any keys discovered on endpoints.
- Deploy continuous monitoring for anomalous SSH connections and scheduled‑task creation.
Source: Microsoft Security Blog
Technical Notes –
- Attack vector: malicious browser extension (malware).
- Persistence: scheduled task that restores the SSH key after reboot.
- Data exposed: potential full filesystem access via SSH.
- No public CVE; the technique exploits trusted OS mechanisms rather than a software flaw.
Source: same as above