Zero-day vulnerability in Palo Alto PAN-OS

Out-of-bounds write
CVE-2026-0300

Not patched

Vulnerability details

Advisory: SB2026050606 - Buffer overflow in User-ID Authentication Portal on Palo Alto PAN-OS

Vulnerable component: Palo Alto PAN-OS

CVE-ID: CVE-2026-0300

CVSSv3 score: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H/E:H/RL:U/RC:C

CWE-ID: CWE-787 - Out-of-bounds write

Description:

The vulnerability allows a remote attacker to compromise vulnerable system.

The vulnerability exists due to a boundary error within the User-ID Authentication Portal (aka Captive Portal) service. A remote attacker can send specially crafted packets to the device, trigger an out-of-bounds write and execute arbitrary code with root privileges on the PA-Series and VM-Series firewalls.

Note, the vulnerability is being actively exploited in the wild.

External links:

https://security.paloaltonetworks.com/CVE-2026-0300

About zero-day vulnerabilities

Zero-day vulnerability is an undisclosed vulnerability in software that hackers can exploit to compromise computer programs, gain unauthorized access to sensitive data, penetrate networks, etc. We consider vulnerability a zero-day when there is no solution provided from software vendor and the vulnerability is being actively exploited by malicious actors.

Zero-day candidate is a potential zero-day vulnerability in software which might have been used in targeted attacks, however there is no evidence to support this suggestion.