Malicious UNC4841 SSH Backdoor Persistence via Non-Standard Port and AllowUsers Restriction (via process_creation)

ATT&CK techniques

Persistence → C2

Recon
Resource Dev
Initial Access
Execution
Persistence
- T1098.004SSH Authorized Keys
Priv Esc
- T1098.004SSH Authorized Keys
Defense Evasion
Cred Access
Discovery
Lateral Movement
Collection
C2
- T1571Non-Standard Port
Exfiltration
Impact

What it detects

This rule detects an sshd process being launched on a high non-standard port while restricting logins to a hardcoded attacker account through the -oAllowUsers option. UNC4841 used this technique to maintain covert SSH access to compromised Barracuda ESG appliances following CVE-2023-2868 exploitation. Establishing a dedicated backdoor listener scoped to a single attacker user provides resilient remote access that blends with legitimate SSH traffic.

Reporting behind it

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Malicious UNC4841 SSH Backdoor Persistence via Non-Standard Port and AllowUsers Restriction (via process_creation)

Pivot detection · T1098.004 · 9 related

Detection content is published as a reviewed draft. Tune thresholds and exclusions against your own telemetry before enabling this rule for alerting.

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