Detect Adobe Acrobat and Reader Prototype Pollution Vulnerability (CVE-2026-34621) in Google Chronicle
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
YARA-L Detection Query
rule cve_2026_34621_adobe_acrobat_prototype_pollution {
meta:
author = "df00tech Detection Engineering"
description = "Detects CVE-2026-34621 Adobe Acrobat prototype pollution exploitation via suspicious child process activity"
severity = "CRITICAL"
priority = "HIGH"
reference = "https://helpx.adobe.com/security/products/acrobat/apsb26-43.html"
events:
$proc.metadata.event_type = "PROCESS_LAUNCH"
$proc.principal.process.file.full_path = /(?i)(AcroRd32\.exe|Acrobat\.exe|AdobeCollabSync\.exe)/
$proc.target.process.file.full_path = /(?i)(cmd\.exe|powershell\.exe|wscript\.exe|cscript\.exe|mshta\.exe|regsvr32\.exe|rundll32\.exe|certutil\.exe|bitsadmin\.exe)/
$proc.principal.hostname = $hostname
match:
$hostname over 5m
outcome:
$risk_score = max(
if($proc.target.process.file.full_path = /(?i)(powershell|mshta)/, 95, 70)
)
$child_proc = array_distinct($proc.target.process.file.full_path)
$parent_proc = array_distinct($proc.principal.process.file.full_path)
$user = array_distinct($proc.principal.user.userid)
condition:
$proc
}Chronicle YARA-L rule detecting Adobe Acrobat and Reader spawning LOLBin child processes as an indicator of CVE-2026-34621 prototype pollution exploitation, with risk scoring.
Data Sources
Required Tables
False Positives & Tuning
- Legitimate PDF automation pipelines using Acrobat JavaScript to trigger system commands
- Enterprise document management systems that use Acrobat as a rendering engine with scripted outputs
- Adobe Acrobat plugin ecosystems that legitimately spawn helper processes
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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