Overview
CVE-2026-0300 identifies a critical out-of-bounds write vulnerability within the User-ID Authentication Portal (Captive Portal) service of Palo Alto Networks PAN-OS. This flaw enables an unauthenticated attacker to execute arbitrary code with root privileges on affected PA-Series and VM-Series firewalls. Given the unauthenticated nature and root-level impact, this vulnerability poses a severe risk to network perimeter security.
Technical Analysis
- Vulnerability Type: Out-of-bounds write.
- Affected Service: User-ID Authentication Portal (also known as Captive Portal).
- Attack Vector: An unauthenticated attacker can exploit this vulnerability by sending specially crafted packets to the affected service.
- Impact: Successful exploitation leads to arbitrary code execution with root privileges on the firewall.
- Affected Products: Palo Alto Networks PA-Series and VM-Series firewalls.
- Affected Versions: Specific affected PAN-OS versions are not detailed in the provided source material. Defenders should consult official Palo Alto Networks advisories for version specifics.
Detection
- Log Sources: Monitor firewall system logs, User-ID logs, and network traffic logs for anomalies related to the Captive Portal service.
- Behavioral Indicators:
- Unexpected reboots or crashes of the firewall.
- Unusual or high CPU/memory utilization on the firewall, particularly associated with the Captive Portal process.
- Detection of new, unauthorized processes running with root privileges.
- Unusual network traffic patterns directed at the firewall’s Captive Portal interface from untrusted sources.
- Alerts from intrusion detection/prevention systems (IDS/IPS) for malformed packets or exploit attempts targeting the Captive Portal.
- Hunt Ideas: Search for connections to the Captive Portal service from external or untrusted networks that exhibit unusual packet sizes, fragmentation, or non-standard protocol behavior.
Mitigations
- Patching: Apply security updates from Palo Alto Networks immediately upon availability. This is the primary and most effective mitigation.
- Disable Service: If the User-ID Authentication Portal (Captive Portal) is not actively used or required, disable the service to remove the attack surface.
- Restrict Access: Implement network access controls (ACLs) to limit which source IP addresses can reach the Captive Portal service on the firewall. Restrict access to only trusted internal networks or specific management IPs.
- Network Segmentation: Ensure firewalls are properly segmented from untrusted networks, and that the Captive Portal interface is not directly exposed to the internet unless absolutely necessary.
- Monitor Logs: Continuously monitor firewall logs for signs of exploitation attempts or unusual activity related to the Captive Portal service.
References
- https://nvd.nist.gov/vuln/detail/CVE-2026-0300
Indicators of Compromise
No public IOCs available at time of writing.