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Potential Linux Reverse Connection through Port Knocking

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Potential Linux Reverse Connection through Port Knocking

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Monitors for a sequence of network activity on atypical ports, prior to receiving a single packet on such a non-standard port, which potentially indicates signal port knocking activity. Port knocking is a covert method of externally opening ports by sending a sequence of packets to previously closed ports, which adversaries may leverage to discreetly gain access without directly alerting traditional monitoring systems.

Rule type: eql

Rule indices:

logs-endpoint.events.*
logs-network_traffic.*

Severity: low

Risk score: 21

Runs every: 5m

Searches indices from: now-9m (Date Math format, see also Additional look-back time)

Maximum alerts per execution: 100

References:

https://github.com/f0rb1dd3n/Reptile

Tags:

Domain: Endpoint
OS: Linux
Use Case: Threat Detection
Tactic: Command and Control
Data Source: Elastic Defend
Rule Type: BBR

Version: 1

Rule authors:

Elastic

Rule license: Elastic License v2

Rule query

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sequence by host.id with maxspan=10s
  [network where host.os.type == "linux" and event.action in ("connection_accepted", "connection_attempted") and
    event.type == "start" and process.name : "*" and (
      process.name : (
        "python*", "php*", "perl*", "ruby", "lua*", "openssl", "nc", "netcat", "ncat", "telnet",
        "awk", "gawk", "mawk", "nawk", "bash", "dash", "sh", "tcsh", "csh", "zsh", "ksh"
      ) or not process.executable : ("/usr/bin/*", "/bin/*")
    ) and not (
       cidrmatch(destination.ip, "127.0.0.0/8", "169.254.0.0/16", "224.0.0.0/4", "::1") or destination.port in (
         20, 21, 22, 23, 25, 53, 67, 68, 69, 80, 110, 123, 137, 138, 139, 143, 161, 162, 179, 443, 445, 465, 514, 515,
         587,636, 989, 990, 993, 995, 1025, 1026, 1080, 1194, 1433, 1434, 1521, 1701, 1723, 1812, 1813, 2082, 2083, 2086,
         2087, 2095, 2096, 2121, 2483, 2484, 3306, 3389, 3478, 3497, 3544, 3689, 3784, 3785, 389, 3998, 5060, 5061, 5190,
         5222, 5223, 5228, 5432, 5500, 554, 5631, 5632, 5800, 5801, 5900, 5901, 8000, 8008, 8080, 8081, 8443, 8888, 9100,
         9200, 9443, 10000
       ) or source.port in (
         20, 21, 22, 23, 25, 53, 67, 68, 69, 80, 110, 123, 137, 138, 139, 143, 161, 162, 179, 443, 445, 465, 514, 515,
         587, 636, 989, 990, 993, 995, 1025, 1026, 1080, 1194, 1433, 1434, 1521, 1701, 1723, 1812, 1813, 2082, 2083, 2086,
         2087, 2095, 2096, 2121, 2483, 2484, 3306, 3389, 3478, 3497, 3544, 3689, 3784, 3785, 389, 3998, 5060, 5061, 5190,
         5222, 5223, 5228, 5432, 5500, 554, 5631, 5632, 5800, 5801, 5900, 5901, 8000, 8008, 8080, 8081, 8443, 8888, 9100,
         9200, 9443, 10000)
      )
  ] by destination.ip
  [network where event.dataset == "network_traffic.flow" and host.os.type == "linux" and event.action == "network_flow"
    and event.type == "connection" and source.packets == 1 and flow.final == false and not (
      cidrmatch(destination.ip, "127.0.0.0/8", "169.254.0.0/16", "224.0.0.0/4", "::1") or destination.port in (
        20, 21, 22, 23, 25, 53, 67, 68, 69, 80, 110, 123, 137, 138, 139, 143, 161, 162, 179, 443, 445, 465, 514, 515,
        587,636, 989, 990, 993, 995, 1025, 1026, 1080, 1194, 1433, 1434, 1521, 1701, 1723, 1812, 1813, 2082, 2083, 2086,
        2087, 2095, 2096, 2121, 2483, 2484, 3306, 3389, 3478, 3497, 3544, 3689, 3784, 3785, 389, 3998, 5060, 5061, 5190,
        5222, 5223, 5228, 5432, 5500, 554, 5631, 5632, 5800, 5801, 5900, 5901, 8000, 8008, 8080, 8081, 8443, 8888, 9100,
        9200, 9443, 10000
      ) or source.port in (
        20, 21, 22, 23, 25, 53, 67, 68, 69, 80, 110, 123, 137, 138, 139, 143, 161, 162, 179, 443, 445, 465, 514, 515,
        587, 636, 989, 990, 993, 995, 1025, 1026, 1080, 1194, 1433, 1434, 1521, 1701, 1723, 1812, 1813, 2082, 2083, 2086,
        2087, 2095, 2096, 2121, 2483, 2484, 3306, 3389, 3478, 3497, 3544, 3689, 3784, 3785, 389, 3998, 5060, 5061, 5190,
        5222, 5223, 5228, 5432, 5500, 554, 5631, 5632, 5800, 5801, 5900, 5901, 8000, 8008, 8080, 8081, 8443, 8888, 9100,
        9200, 9443, 10000)
      )
  ] by source.ip

Framework: MITRE ATT&CK^TM

Tactic:
- Name: Command and Control
- ID: TA0011
- Reference URL: https://attack.mitre.org/tactics/TA0011/
Technique:
- Name: Non-Standard Port
- ID: T1571
- Reference URL: https://attack.mitre.org/techniques/T1571/
Technique:
- Name: Traffic Signaling
- ID: T1205
- Reference URL: https://attack.mitre.org/techniques/T1205/
Sub-technique:
- Name: Port Knocking
- ID: T1205.001
- Reference URL: https://attack.mitre.org/techniques/T1205/001/
Tactic:
- Name: Defense Evasion
- ID: TA0005
- Reference URL: https://attack.mitre.org/tactics/TA0005/

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