Detect Adobe Acrobat and Reader Prototype Pollution Vulnerability (CVE-2026-34621) in Splunk
Detects exploitation of CVE-2026-34621, a prototype pollution vulnerability (CWE-1321) in Adobe Acrobat and Reader. This KEV-listed vulnerability allows attackers to manipulate JavaScript object prototypes within PDF processing, potentially leading to arbitrary code execution, privilege escalation, or sandbox escape. Exploitation typically occurs via malicious PDF documents that trigger prototype chain manipulation during rendering or form processing.
MITRE ATT&CK
SPL Detection Query
index=endpoint sourcetype IN ("XmlWinEventLog:Microsoft-Windows-Sysmon/Operational", "WinEventLog:Security", "crowdstrike:events:sensor")
| eval parent_image=coalesce(ParentImage, parent_process_name, InitiatingProcessFileName)
| eval child_image=coalesce(Image, process_name, FileName)
| where match(parent_image, "(?i)(AcroRd32\.exe|Acrobat\.exe|AdobeCollabSync\.exe)")
| where match(child_image, "(?i)(cmd\.exe|powershell\.exe|wscript\.exe|cscript\.exe|mshta\.exe|regsvr32\.exe|rundll32\.exe|certutil\.exe|bitsadmin\.exe|wmic\.exe|curl\.exe|wget\.exe)")
| eval risk_score=case(
match(child_image, "(?i)(powershell|mshta|regsvr32)"), 90,
match(child_image, "(?i)(cmd|wscript|cscript)"), 75,
true(), 60
)
| table _time, host, user, parent_image, CommandLine, child_image, ParentCommandLine, risk_score
| join type=left host [
search index=endpoint sourcetype IN ("XmlWinEventLog:Microsoft-Windows-Sysmon/Operational")
| eval net_parent=coalesce(Image, process_name)
| where match(net_parent, "(?i)(AcroRd32\.exe|Acrobat\.exe)")
| where DestinationPort IN (80, 443, 4444, 8080, 1337)
| stats values(DestinationIp) as c2_candidates, values(DestinationPort) as ports by host
]
| sort - risk_score
| eval detection="CVE-2026-34621 Adobe Acrobat Prototype Pollution"Detects suspicious child process spawning from Adobe Acrobat and Reader processes, correlated with potential C2 network activity, indicative of CVE-2026-34621 prototype pollution exploitation.
Data Sources
Required Sourcetypes
False Positives & Tuning
- Legitimate Acrobat JavaScript workflows that invoke system utilities for printing or export
- Enterprise DLP solutions that hook into Acrobat and spawn child processes for content scanning
- Adobe Creative Cloud update services that run alongside Acrobat
- Legitimate Acrobat plugin installers that require post-install scripting
Other platforms for CVE-2026-34621
Testing Methodology
Validate this detection against 4 adversary techniques from Atomic Red Team. Each test below lists the behaviour to exercise and the telemetry you should expect to see. Executable commands and cleanup steps are available with Pro.
- Test 1Simulate Acrobat Prototype Pollution Child Process Spawn (Windows)
Expected signal: Sysmon Event ID 1: Process Create with ParentImage matching AcroRd32.exe and Image matching cmd.exe; DeviceProcessEvents in MDE showing the parent-child relationship
- Test 2Simulate Acrobat JavaScript Prototype Pollution Payload (PDF)
Expected signal: File creation event for .js file in temp directory; if embedded in PDF and opened in Acrobat, Sysmon Event ID 11 file create events and JavaScript engine activity
- Test 3Simulate Acrobat-Initiated Outbound Network Connection (C2 Beacon Pattern)
Expected signal: Sysmon Event ID 3: Network connection from AcroRd32.exe to 127.0.0.1:4444; DeviceNetworkEvents in MDE showing Acrobat making a connection to port 4444
- Test 4Acrobat Suspicious File Drop in AppData (Post-Exploitation Staging)
Expected signal: Sysmon Event ID 11: File created at %APPDATA%\adobe_helper.exe with Image matching AcroRd32.exe; DeviceFileEvents in MDE with InitiatingProcessFileName = AcroRd32.exe and FolderPath in AppData
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Get the full detection package for CVE-2026-34621 including response playbook, investigation guide, and atomic red team tests.