Suspicious Linux VSFTPD Errors

Rule ID

PH_Rule_TH_Linux_39

Default Status

Enabled

Description

Detects suspicious VSFTPD error messages that indicate a fatal or suspicious error that could be caused by exploit attempts

Severity

MITRE ATT&CK® Tactics

Execution

Execution consists of techniques that result in adversary-controlled code running on a local or remote system. Techniques that run malicious code are often paired with techniques from all other tactics to achieve broader goals, like exploring a network or stealing data. For example, an adversary might use a remote access tool to run a PowerShell script that does Remote System Discovery.

https://attack.mitre.org/tactics/TA0002

MITRE ATT&CK® Techniques

No Technique Specified

Impacts

Server

Data Source

Linux via Syslog

Detection

Correlation

Remediation Guidance

No remediation guidance specified

Time Window

If the following pattern or patterns match an ingested event within the given time window in seconds, trigger an incident.

300 seconds

Trigger Conditions

If the following defined pattern/s occur within a 300 second time window.

Download

SubPattern Definitions

SubPattern Name: Download

This is the named definition of the event query, this is important if multiple subpatterns are defined to distinguish them.

SubPattern Query

This is the query logic that matches incoming events

eventType CONTAIN "Generic_Unix_" AND
          (rawEventMsg CONTAIN "Connection refused: too many sessions for this address" OR
          rawEventMsg CONTAIN "Connection refused: tcp_wrappers denial" OR
          rawEventMsg CONTAIN "Bad HTTP verb" OR
          rawEventMsg CONTAIN "port and pasv both active" OR
          rawEventMsg CONTAIN "pasv and port both active" OR
          rawEventMsg CONTAIN "Transfer done (but failed to open directory)" OR
          rawEventMsg CONTAIN "Could not set file modification time" OR
          rawEventMsg CONTAIN "bug: pid active in ptrace_sandbox_free" OR
          rawEventMsg CONTAIN "PTRACE_SETOPTIONS failure" OR
          rawEventMsg CONTAIN "weird status:" OR
          rawEventMsg CONTAIN "couldn't handle sandbox event" OR
          rawEventMsg CONTAIN "syscall not permitted" OR
          rawEventMsg CONTAIN "syscall validate failed" OR
          rawEventMsg CONTAIN "Input line too long" OR
          rawEventMsg CONTAIN "poor buffer accounting in str_netfd_alloc" OR
          rawEventMsg CONTAIN "vsf_sysutil_read_loop" OR
          rawEventMsg REGEXP ".*syscall .* out of bounds.*") AND phEventCategory = 0

Group by Attributes

This defines how matching events are aggregated, only events with the same matching attribute values are grouped into one unique incident ID

reptDevName

Aggregate Constraint

This is most typically a numerical constraint that defines when the rule should trigger an incident

COUNT(*) >= 1

Incident Attribute Mapping

This section defines which fields in matching raw events should be mapped to the incident attributes in the resulting incident.

The available raw event attributes to map are limited to the group by attributes and the aggregate event constraint fields for each subpattern

 hostName = Download.reptDevName

FortiSIEM Rules