Query: detect The DNS Z flag is bit within the DNS protocol header that is, per the IETF design, meant to be used reserved (unused). A in logs
Matching passage: Sigma rule: The DNS Z flag is bit within the DNS protocol header that is, per the IETF design, meant to be used reserved (unused). A. Logsource: zeek / dns. Rule: title: Suspicious DNS Z Flag Bit Set id: ede05abc-2c9e-4624-9944-9ff17fdc0bf5 status: test description: 'The DNS Z flag is bit within the DNS protocol header that is, per the IETF design, meant to be used reserved (unused). Although recently it has been used in DNSSec, the value being set to anything other than 0 should be rare. Otherwise if it is set to non 0 and DNSSec is being used, then excluding the legitimate domains is low effort and high reward. Determine if multiple of these files were accessed in a short period of time to further enhance the possibility of seeing if this was a one off or the possibility of larger sensitive file gathering. This Sigma query is designed to accompany the Corelight Threat Hunting Guide, which can be found here: https://www3.corelight.com/corelights-introductory-guide-to-threat-hunting-with-zeek-bro-logs'' ' references: - https://twitter.com/neu5ron/status/1346245602502443009 - https://tdm.socprime.com/tdm/info/eLbyj4JjI15v#sigma - https://tools.ietf.org/html/rfc2929#section-2.1 - https://www.netresec.com/?page=Blog&month=2021-01&post=Finding-Targeted-SUNBURST-Victims-with-pDNS author: '@neu5ron, SOC Prime Team, Corelight' date: 2021-05-04 modified: 2022-11-29 tags: - attack.t1095 - attack.t1571 - attack.command-and-control logsource: product: zeek service: dns detection: z_flag_unset: Z: 0 most_probable_valid_domain: query|contains: . exclude_tlds: query|endswith: - .arpa - .local - .ultradns.net - .twtrdns.net - .azuredns-prd.info - .azure-dns.com - .azuredns-ff.info - .azuredns-ff.org - .azuregov-dns.org exclude_query_types: qtype_name: - ns - mx exclude_responses: answers|endswith: \\x00 exclude_netbios: id.resp_p: - 137 - 138 - 139 condition: not z_flag_unset and most_probable_valid_domain and not (exclude_tlds or exclude_query_types or exclude_responses or exclude_netbios) falsepositives: - Internal or legitimate external domains using DNSSec. Verify if these are legitimate DNSSec domains and then exclude them. - If you work in a Public Sector then it may be good to exclude things like endswith ".edu", ".gov" and or ".mil" level: medium
Near-miss passage: Sigma rule: Detects the OpenEDR ssh-shellhost.exe spawning a command shell (cmd.exe) or PowerShell with PTY (pseudo-terminal) capabi. Logsource: windows / process_creation. Rule: title: OpenEDR Spawning Command Shell id: 7f3a9c2d-4e8b-4a7f-9d3e-5c6f8a9b2e1d status: experimental description: 'Detects the OpenEDR ssh-shellhost.exe spawning a command shell (cmd.exe) or PowerShell with PTY (pseudo-terminal) capabilities. This may indicate remote command execution through OpenEDR''s remote management features, which could be legitimate administrative activity or potential abuse of the remote access tool. Threat actors may leverage OpenEDR''s remote shell capabilities to execute commands on compromised systems, facilitating lateral movement or other command-and-control operations. ' author: '@kostastsale' date: 2026-02-19 references: - https://kostas-ts.medium.com/detecting-abuse-of-openedrs-permissive-edr-trial-a-security-researcher-s-perspective-fc55bf53972c tags: - attack.execution - attack.t1059.003 - attack.lateral-movement - attack.t1021.004 - attack.command-and-control - attack.t1219 logsource: product: windows category: process_creation detection: selection_img: ParentImage|endswith: \ITSMService.exe Image|endswith: \ssh-shellhost.exe CommandLine|contains: --pty selection_cli_shell: CommandLine|contains: - bash - cmd - powershell - pwsh condition: all of selection_* falsepositives: - Legitimate use of OpenEDR for remote command execution level: medium