CVE-2026-0300: Palo Alto Networks PAN-OS User-ID RCE — Detection and Hardening Guide | Security Arsenal

Palo Alto Networks has confirmed that threat actors are actively exploiting CVE-2026-0300, a critical buffer overflow vulnerability in the PAN-OS User-ID Authentication Portal service. With a CVSS score of 9.3, this flaw allows unauthenticated attackers to execute arbitrary code with root privileges.

Based on intelligence indicating exploitation attempts as early as April 9, 2026, this is not a theoretical risk. The attack chain is simple: send a malicious packet to the exposed User-ID service, achieve remote code execution (RCE) as root, and establish a foothold for espionage or data exfiltration. For defenders, this requires immediate action—identifying exposed management surfaces and applying emergency patches.

Technical Analysis

Vulnerability Details:

CVE ID: CVE-2026-0300
CVSS Score: 9.3 (Critical)
Affected Component: User-ID Authentication Portal service (useridd)
Impact: Unauthenticated RCE with Root privileges

Affected Products & Versions:

PAN-OS 10.2 earlier than specific hotfixes
PAN-OS 11.1 earlier than specific hotfixes
PAN-OS 11.2 earlier than specific hotfixes (Refer to the official advisory for the exact matrix, but assume all standard deployments using the User-ID feature are in scope.)

Attack Chain (Defender's View):

Reconnaissance: The attacker scans for PAN-OS management interfaces or distinct User-ID portal ports exposed to the internet (often TCP 443 or custom ports).
Exploitation: The actor sends a specifically crafted HTTP request to the User-ID Authentication Portal endpoint. This request triggers a buffer overflow in the underlying C/C++ code.
Privilege Escalation & Execution: The overflow overwrites the instruction pointer, redirecting execution to a shellcode payload. Because the service runs as root, the attacker immediately gains full system control.
Espionage/Persistence: The actor may deploy backdoors, harvest configuration data (VPN credentials, SSL keys), or move laterally into the protected network.

Exploitation Status: Confirmed active exploitation. Threat actors have been probing and attempting to exploit this vulnerability since at least April 9, 2026. The intent appears to be espionage-oriented rather than disruptive.

Detection & Response

Detection of this vulnerability relies heavily on logging for the PAN-OS management plane. Since the User-ID service handles authentication and redirection, abnormal termination of the useridd process or suspicious web access logs are the primary indicators.

Sigma Rules

YAML

---
title: Potential PAN-OS User-ID Exploit Attempt via Web Portal
id: 86d7c4d1-9e3a-4b12-8f9e-123456789abc
status: experimental
description: Detects potential exploitation of CVE-2026-0300 by identifying access to the User-ID Authentication Portal with abnormal HTTP methods or suspicious path traversal attempts.
references:
 - https://security.paloaltonetworks.com/CVE-2026-0300
author: Security Arsenal
date: 2026/05/12
tags:
 - attack.initial_access
 - attack.t1190
logsource:
 category: web
 product: pan-os
detection:
 selection:
   cs-method|contains:
     - 'POST'
   cs-uri-path|contains:
     - '/user-auth'
     - '/global-protect/portal/'
   cs-uri-query|contains:
     - '..'
     - '%2e%2e'
   sc-status:
     - 400
     - 500
 condition: selection
falsepositives:
 - Legitimate but misconfigured User-ID redirects
level: high
---
title: PAN-OS User-ID Process Crash (useridd)
id: b2e4f8a1-0d9c-4a5b-8e1f-9876543210ab
status: experimental
description: Detects crashes of the PAN-OS User-ID daemon (useridd), which may indicate a failed buffer overflow exploit attempt against CVE-2026-0300.
references:
 - https://security.paloaltonetworks.com/CVE-2026-0300
author: Security Arsenal
date: 2026/05/12
tags:
 - attack.initial_access
 - attack.t1190
logsource:
 product: pan-os
 category: system
detection:
 selection:
   event_id:
     - 'SYSTEM_EXIT'
     - 'PROCESS_EXIT'
   process_name|contains:
     - 'useridd'
   exit_reason|contains:
     - 'SIGSEGV'
     - 'SIGABRT'
 condition: selection
falsepositives:
 - Rare service restart due to configuration changes
level: critical

KQL (Microsoft Sentinel)

KQL — Microsoft Sentinel / Defender

// Hunt for PAN-OS User-ID Portal exploitation indicators
Syslog
| where DeviceVendor == "Palo Alto Networks"
| where SyslogMessage has "user-id" 
| extend ProcessName = extract(@"process_name:(\S+)", 1, SyslogMessage), 
         StatusCode = extract(@"status_code:(\d+)", 1, SyslogMessage),
         URL = extract(@"url:(\S+)", 1, SyslogMessage)
// Filter for crashes or suspicious web access
| where ProcessName contains "useridd" 
    or (URL has @"/user-auth" and StatusCode in ("400", "500"))
| project TimeGenerated, DeviceName, ProcessName, URL, StatusCode, SyslogMessage
| sort by TimeGenerated desc

Velociraptor VQL

VQL — Velociraptor

-- Hunt for PAN-OS management logs indicating User-ID service crashes or suspicious access
SELECT * FROM parse_lines_with_regex(
    filename=glob('/var/log/pan/*.log'),
    regex='(?P<timestamp>\S+ \S+) \S+ (?P<process>\S+): (?P<message>.*)'
)
WHERE process =~ 'useridd' 
  AND (message =~ 'segfault' 
       OR message =~ 'exiting abnormally' 
       OR message =~ 'overflow')

Remediation Script (Bash)

Bash / Shell

#!/bin/bash
# PAN-OS CVE-2026-0300 Verification Script
# Run this on a management jump host or via API wrapper. 
# This is a template for SSH-based auditing.

TARGET_HOST="your-firewall-ip"
ADMIN_USER="admin"

echo "Checking User-ID Authentication Portal status and version..."

# Check if User-ID is configured and listening
# Note: Actual CLI commands require SSH access. 
# This script simulates the logic for an API-based check.

# 1. Check Software Version
# "show system info" | grep "sw-version"
# 2. Check Management Configuration
# "show management config" | grep "user-id"
# 3. Check Commit History for recent crashes
# "show log system" | match "segfault"

echo "Manual verification required: Ensure PAN-OS is upgraded to the latest security hotfix for CVE-2026-0300."
echo "Action: Disable User-ID Authentication Portal if not explicitly required for operations."

Remediation

Immediate remediation is required to prevent root-level compromise.

Apply Patches: Update to the latest PAN-OS versions that address CVE-2026-0300. Refer to the official Palo Alto Networks Security Advisory (PAN-SA-2026-0012).
Disable Vulnerable Component: If the User-ID Authentication Portal is not required for your network architecture, disable it immediately via the Management Interface.
- Path: Device > User Identification > Authentication Portal
Restrict Access: If the feature is required, ensure the service is not exposed to the internet. Restrict access to trusted internal IP subnets only using Management Interface profiles.
Audit Logs: Review system logs for indicators of compromise (IOCs) dating back to April 9, 2026. Look for useridd process crashes or suspicious configuration changes.

Related Resources

Security Arsenal Penetration Testing Services AlertMonitor Platform Book a SOC Assessment vulnerability-management Intel Hub

CVE-2026-0300: Palo Alto Networks PAN-OS User-ID RCE — Detection and Hardening Guide