On May 6, 2026, Palo Alto Networks published a security advisory for CVE-2026-0300, a critical unauthenticated buffer overflow vulnerability affecting PAN-OS PA-Series and VM-Series firewall appliances. Prisma Access, Cloud NGFW, and Panorama appliances are not affected by this vulnerability.
The vulnerability carries a CVSSv4 score of 9.3 and has been confirmed as exploited in the wild by the vendor. CVE-2026-0300 is a buffer overflow (CWE-787) in the User-ID™ Authentication Portal (also known as Captive Portal), a non-default PAN-OS feature used to map IP addresses to usernames. An unauthenticated remote attacker can exploit this vulnerability by sending specially crafted packets to a device with the Authentication Portal enabled, achieving arbitrary code execution with root privileges on the affected firewall. No authentication or user interaction is required.
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Source: Rapid7
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