Malicious Immutable Flag on SSH authorized_keys via chattr

ATT&CK techniques

Persistence → Defense Evasion

Recon
Resource Dev
Initial Access
Execution
Persistence
- T1098.004SSH Authorized Keys
Priv Esc
- T1098.004SSH Authorized Keys
Defense Evasion
- T1222.002Linux and Mac Permissions
Cred Access
Discovery
Lateral Movement
Collection
C2
Exfiltration
Impact

What it detects

This rule detects use of chattr to set or clear the immutable attribute on an SSH authorized_keys file. Linux intrusion actors inject a backdoor key and then mark authorized_keys immutable so defenders and competing actors cannot remove their persistent access.

Reporting behind it

Related detections9 linkedT1098.004 — drag to rearrange

Suspicious SSH Daemon Configuration Change Enabling Root Login

Suspicious SSH Authorized Keys Modification via Scripting Interpreter on Linux via Process Creation (via process_creation)

Malicious SSH authorized_keys Overwrite With Outlaw Marker

Malicious SSH authorized_keys Modification for Persistence on Appliance

Malicious vmanage-admin Public Key Authentication in SSH Auth Log

Suspicious File Immutability Set via chattr to Resist Removal

Suspicious File Immutability via chattr

Suspicious SSH authorized_keys Modification for Persistence

Malicious Immutable Attribute Set on SSH Authorized Keys via chattr on Linux

Malicious Immutable Flag on SSH authorized_keys via chattr

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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