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 Making a File Executable in a Temp Directory (via process_creation)

Suspicious SSH authorized_keys Persistence Modification (via process_creation)

Malicious EtherRAT SSH authorized_keys Backdoor Injection via Shell (via process_creation)

Suspicious File Immutability Manipulation via chattr

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

Malicious SSH authorized_keys Modification Following Web Server Compromise (via process_creation)

Suspicious Modification of SSH Authorized Keys on SD-WAN Appliance by UAT-8616

Suspicious Download to tmp Followed by chmod Execution on Linux

Linux: chattr Used to Remove Immutable File Attribute

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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