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Detection rules › YARA-L

Lsass Memory Dump via Comsvcs DLL

Severity
high
Type
Detection
Time window
5m
Match by
hostname
Author
Roberto Rodriguez (Cyb3rWard0g), OTR (Open Threat Research)
Source
github.com/chronicle/detection-rules

Detects adversaries leveraging the MiniDump export function from comsvcs.dll via rundll32 to perform a memory dump from lsass

MITRE ATT&CK coverage

TacticTechniques
Credential AccessT1003.001 OS Credential Dumping: LSASS Memory

References

Event coverage

ProviderEventTitle
SysmonEvent ID 10ProcessAccess

Rule body yaral

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 * Copyright 2025 Google LLC
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 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     https://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

rule lsass_memory_dump_comsvcs_dll {

  meta:
    author = "Roberto Rodriguez (Cyb3rWard0g), OTR (Open Threat Research)"
    description = "Detects adversaries leveraging the MiniDump export function from comsvcs.dll via rundll32 to perform a memory dump from lsass"
    reference = "https://github.com/SigmaHQ/sigma/blob/master/rules/windows/process_access/proc_access_win_lsass_dump_comsvcs_dll.yml"
    license = "https://github.com/SigmaHQ/Detection-Rule-License/blob/main/LICENSE.Detection.Rules.md"
    rule_name = "Lsass Memory Dump via Comsvcs DLL"
    sigma_uuid = "a49fa4d5-11db-418c-8473-1e014a8dd462"
    sigma_status = "test"
    rule_id = "mr_4efe14fb-53fb-49ba-b137-f5d70cb6adb9"
    tactic = "TA0006"
    technique = "T1003.001"
    type = "Detection"
    data_source = "Sysmon"
    platform = "Windows"
    severity = "High"
    priority = "High"
    false_positives = "Unknown"

  events:
    $process.metadata.event_type = "PROCESS_OPEN"
    re.regex($process.target.process.file.full_path, `\\lsass\.exe$`) nocase
    re.regex($process.principal.process.file.full_path, `\\rundll32\.exe$`) nocase
    strings.contains(strings.to_lower($process.additional.fields["CallTrace"]), "comsvcs.dll")

    $process.principal.hostname = $hostname

  match:
    $hostname over 5m

  outcome:
    //example usage of specifying test hostname to adjust risk score
    $risk_score = max(if($process.principal.hostname = "hostname", 0, 15))
    $principal_process_pid = array_distinct($process.principal.process.pid)
    $principal_process_command_line = array_distinct($process.principal.process.command_line)
    $principal_process_file_sha256 = array_distinct($process.principal.process.file.sha256)
    $principal_process_file_full_path = array_distinct($process.principal.process.file.full_path)
    $principal_process_product_specfic_process_id = array_distinct($process.principal.process.product_specific_process_id)
    $principal_process_parent_process_product_specfic_process_id = array_distinct($process.principal.process.parent_process.product_specific_process_id)
    $target_process_pid = array_distinct($process.target.process.pid)
    $target_process_command_line = array_distinct($process.target.process.command_line)
    $target_process_file_sha256 = array_distinct($process.target.process.file.sha256)
    $target_process_file_full_path = array_distinct($process.target.process.file.full_path)
    $target_process_product_specfic_process_id = array_distinct($process.target.process.product_specific_process_id)
    $log_type = array_distinct(strings.concat($process.metadata.log_type,"/",$process.metadata.product_event_type))

  condition:
    $process
}

Detection logic

Fires when at least one $process event in the 5m window.

Events

$process PROCESS_OPEN (10)

  • target.process.file.full_path matches "\\lsass\.exe$"
  • principal.process.file.full_path matches "\\rundll32\.exe$"
  • additional.fields["CallTrace"] contains "comsvcs.dll"

Correlation

Match key
$hostname (principal.hostname)
Within
5m

Outcome

Fields the detection emits on a match. $risk_score drives alerting; Chronicle surfaces the rest on the detection.

FieldExpression
risk_scoremax(if($process.principal.hostname = "hostname", 0, 15))
principal_process_pidarray_distinct($process.principal.process.pid)
principal_process_command_linearray_distinct($process.principal.process.command_line)
principal_process_file_sha256array_distinct($process.principal.process.file.sha256)
principal_process_file_full_patharray_distinct($process.principal.process.file.full_path)
principal_process_product_specfic_process_idarray_distinct($process.principal.process.product_specific_process_id)
principal_process_parent_process_product_specfic_process_idarray_distinct($process.principal.process.parent_process.product_specific_process_id)
target_process_pidarray_distinct($process.target.process.pid)
target_process_command_linearray_distinct($process.target.process.command_line)
target_process_file_sha256array_distinct($process.target.process.file.sha256)
target_process_file_full_patharray_distinct($process.target.process.file.full_path)
target_process_product_specfic_process_idarray_distinct($process.target.process.product_specific_process_id)
log_typearray_distinct(strings.concat($process.metadata.log_type,"/",$process.metadata.product_event_type))