Suspicious PDF Reader Child Process

  1[metadata]
  2creation_date = "2020/03/30"
  3integration = ["endpoint", "windows", "system", "m365_defender", "sentinel_one_cloud_funnel", "crowdstrike"]
  4maturity = "production"
  5updated_date = "2026/05/04"
  6
  7[rule]
  8author = ["Elastic"]
  9description = """
 10Identifies suspicious child processes of PDF reader applications. These child processes are often launched via
 11exploitation of PDF applications or social engineering.
 12"""
 13from = "now-9m"
 14index = [
 15    "endgame-*",
 16    "logs-crowdstrike.fdr*",
 17    "logs-endpoint.events.process-*",
 18    "logs-m365_defender.event-*",
 19    "logs-sentinel_one_cloud_funnel.*",
 20    "logs-system.security*",
 21    "logs-windows.forwarded*",
 22    "logs-windows.sysmon_operational-*",
 23    "winlogbeat-*",
 24]
 25language = "eql"
 26license = "Elastic License v2"
 27name = "Suspicious PDF Reader Child Process"
 28note = """## Triage and analysis
 29
 30### Investigating Suspicious PDF Reader Child Process
 31
 32PDF is a common file type used in corporate environments and most machines have software to handle these files. This creates a vector where attackers can exploit the engines and technology behind this class of software for initial access or privilege escalation.
 33
 34This rule looks for commonly abused built-in utilities spawned by a PDF reader process, which is likely a malicious behavior.
 35
 36#### Possible investigation steps
 37
 38- Investigate the process execution chain (parent process tree) for unknown processes. Examine their executable files for prevalence, whether they are located in expected locations, and if they are signed with valid digital signatures.
 39- Investigate other alerts associated with the user/host during the past 48 hours.
 40- Retrieve PDF documents received and opened by the user that could cause this behavior. Common locations include, but are not limited to, the Downloads and Document folders and the folder configured at the email client.
 41- Determine if the collected files are malicious:
 42  - Use a private sandboxed malware analysis system to perform analysis.
 43    - Observe and collect information about the following activities:
 44      - Attempts to contact external domains and addresses.
 45      - File and registry access, modification, and creation activities.
 46      - Service creation and launch activities.
 47      - Scheduled task creation.
 48  - Use the PowerShell `Get-FileHash` cmdlet to get the files' SHA-256 hash values.
 49    - Search for the existence and reputation of the hashes in resources like VirusTotal, Hybrid-Analysis, CISCO Talos, Any.run, etc.
 50
 51
 52### False positive analysis
 53
 54- This activity is unlikely to happen legitimately. Benign true positives (B-TPs) can be added as exceptions if necessary.
 55
 56### Response and remediation
 57
 58- Initiate the incident response process based on the outcome of the triage.
 59- Isolate the involved host to prevent further post-compromise behavior.
 60- Investigate credential exposure on systems compromised or used by the attacker to ensure all compromised accounts are identified. Reset passwords for these accounts and other potentially compromised credentials, such as email, business systems, and web services.
 61- If the triage identified malware, search the environment for additional compromised hosts.
 62  - Implement temporary network rules, procedures, and segmentation to contain the malware.
 63  - Stop suspicious processes.
 64  - Immediately block the identified indicators of compromise (IoCs).
 65  - Inspect the affected systems for additional malware backdoors like reverse shells, reverse proxies, or droppers that attackers could use to reinfect the system.
 66- Remove and block malicious artifacts identified during triage.
 67- Run a full antimalware scan. This may reveal additional artifacts left in the system, persistence mechanisms, and malware components.
 68- Determine the initial vector abused by the attacker and take action to prevent reinfection through the same vector.
 69  - If the malicious file was delivered via phishing:
 70    - Block the email sender from sending future emails.
 71    - Block the malicious web pages.
 72    - Remove emails from the sender from mailboxes.
 73    - Consider improvements to the security awareness program.
 74- Using the incident response data, update logging and audit policies to improve the mean time to detect (MTTD) and the mean time to respond (MTTR).
 75"""
 76
 77setup = """## Setup
 78
 79This rule is designed for data generated by [Elastic Defend](https://www.elastic.co/security/endpoint-security), which provides native endpoint detection and response, along with event enrichments designed to work with our detection rules.
 80
 81Setup instructions: https://ela.st/install-elastic-defend
 82
 83### Additional data sources
 84
 85This rule also supports the following third-party data sources. For setup instructions, refer to the links below:
 86
 87- [CrowdStrike](https://ela.st/crowdstrike-integration)
 88- [Microsoft Defender XDR](https://ela.st/m365-defender)
 89- [SentinelOne Cloud Funnel](https://ela.st/sentinel-one-cloud-funnel)
 90- [Sysmon Event ID 1 - Process Creation](https://ela.st/sysmon-event-1-setup)
 91- [Windows Process Creation Logs](https://ela.st/audit-process-creation)
 92"""
 93
 94risk_score = 21
 95rule_id = "53a26770-9cbd-40c5-8b57-61d01a325e14"
 96severity = "low"
 97tags = [
 98    "Domain: Endpoint",
 99    "OS: Windows",
100    "Use Case: Threat Detection",
101    "Tactic: Execution",
102    "Tactic: Initial Access",
103    "Resources: Investigation Guide",
104    "Data Source: Elastic Endgame",
105    "Data Source: Elastic Defend",
106    "Data Source: Windows Security Event Logs",
107    "Data Source: Microsoft Defender XDR",
108    "Data Source: Sysmon",
109    "Data Source: SentinelOne",
110    "Data Source: Crowdstrike",
111]
112timestamp_override = "event.ingested"
113type = "eql"
114
115query = '''
116process where host.os.type == "windows" and event.type == "start" and
117  process.parent.name : ("AcroRd32.exe",
118                         "Acrobat.exe",
119                         "FoxitPhantomPDF.exe",
120                         "FoxitReader.exe") and
121  process.name : ("arp.exe", "dsquery.exe", "dsget.exe", "gpresult.exe", "hostname.exe", "ipconfig.exe", "nbtstat.exe",
122                  "net.exe", "net1.exe", "netsh.exe", "netstat.exe", "nltest.exe", "ping.exe", "qprocess.exe",
123                  "quser.exe", "qwinsta.exe", "reg.exe", "sc.exe", "systeminfo.exe", "tasklist.exe", "tracert.exe",
124                  "whoami.exe", "bginfo.exe", "cdb.exe", "cmstp.exe", "csi.exe", "dnx.exe", "fsi.exe", "ieexec.exe",
125                  "iexpress.exe", "installutil.exe", "Microsoft.Workflow.Compiler.exe", "msbuild.exe", "mshta.exe",
126                  "msxsl.exe", "odbcconf.exe", "rcsi.exe", "regsvr32.exe", "xwizard.exe", "atbroker.exe",
127                  "forfiles.exe", "schtasks.exe", "regasm.exe", "regsvcs.exe", "cmd.exe", "cscript.exe",
128                  "powershell.exe", "pwsh.exe", "wmic.exe", "wscript.exe", "bitsadmin.exe", "certutil.exe", "ftp.exe")
129'''
130
131
132[[rule.threat]]
133framework = "MITRE ATT&CK"
134
135[[rule.threat.technique]]
136id = "T1203"
137name = "Exploitation for Client Execution"
138reference = "https://attack.mitre.org/techniques/T1203/"
139
140[[rule.threat.technique]]
141id = "T1204"
142name = "User Execution"
143reference = "https://attack.mitre.org/techniques/T1204/"
144
145[[rule.threat.technique.subtechnique]]
146id = "T1204.002"
147name = "Malicious File"
148reference = "https://attack.mitre.org/techniques/T1204/002/"
149
150[rule.threat.tactic]
151id = "TA0002"
152name = "Execution"
153reference = "https://attack.mitre.org/tactics/TA0002/"
154
155[[rule.threat]]
156framework = "MITRE ATT&CK"
157
158[[rule.threat.technique]]
159id = "T1566"
160name = "Phishing"
161reference = "https://attack.mitre.org/techniques/T1566/"
162
163[[rule.threat.technique.subtechnique]]
164id = "T1566.001"
165name = "Spearphishing Attachment"
166reference = "https://attack.mitre.org/techniques/T1566/001/"
167
168[rule.threat.tactic]
169id = "TA0001"
170name = "Initial Access"
171reference = "https://attack.mitre.org/tactics/TA0001/"
172
173[[rule.threat]]
174framework = "MITRE ATT&CK"
175
176[[rule.threat.technique]]
177id = "T1218"
178name = "System Binary Proxy Execution"
179reference = "https://attack.mitre.org/techniques/T1218/"
180
181[[rule.threat.technique.subtechnique]]
182id = "T1218.003"
183name = "CMSTP"
184reference = "https://attack.mitre.org/techniques/T1218/003/"
185
186[[rule.threat.technique.subtechnique]]
187id = "T1218.004"
188name = "InstallUtil"
189reference = "https://attack.mitre.org/techniques/T1218/004/"
190
191[[rule.threat.technique.subtechnique]]
192id = "T1218.005"
193name = "Mshta"
194reference = "https://attack.mitre.org/techniques/T1218/005/"
195
196[[rule.threat.technique.subtechnique]]
197id = "T1218.008"
198name = "Odbcconf"
199reference = "https://attack.mitre.org/techniques/T1218/008/"
200
201[[rule.threat.technique.subtechnique]]
202id = "T1218.009"
203name = "Regsvcs/Regasm"
204reference = "https://attack.mitre.org/techniques/T1218/009/"
205
206[[rule.threat.technique.subtechnique]]
207id = "T1218.010"
208name = "Regsvr32"
209reference = "https://attack.mitre.org/techniques/T1218/010/"
210
211[rule.threat.tactic]
212id = "TA0005"
213name = "Defense Evasion"
214reference = "https://attack.mitre.org/tactics/TA0005/"
215
216[[rule.threat]]
217framework = "MITRE ATT&CK"
218
219[[rule.threat.technique]]
220id = "T1016"
221name = "System Network Configuration Discovery"
222reference = "https://attack.mitre.org/techniques/T1016/"
223
224[[rule.threat.technique.subtechnique]]
225id = "T1016.001"
226name = "Internet Connection Discovery"
227reference = "https://attack.mitre.org/techniques/T1016/001/"
228
229[[rule.threat.technique]]
230id = "T1033"
231name = "System Owner/User Discovery"
232reference = "https://attack.mitre.org/techniques/T1033/"
233
234[[rule.threat.technique]]
235id = "T1057"
236name = "Process Discovery"
237reference = "https://attack.mitre.org/techniques/T1057/"
238
239[[rule.threat.technique]]
240id = "T1082"
241name = "System Information Discovery"
242reference = "https://attack.mitre.org/techniques/T1082/"
243
244[rule.threat.tactic]
245id = "TA0007"
246name = "Discovery"
247reference = "https://attack.mitre.org/tactics/TA0007/"