CVE-2026-0300
Published 2026-05-06 · Updated 2026-10-26 · Source psirt@paloaltonetworks.com
Summary
CVE-2026-0300 is a critical-severity (CVSS 9.8) vulnerability in Palo Alto Networks PAN-OS. CISA added it to the Known Exploited Vulnerabilities catalog on May 6, 2026, which means exploitation in the wild has been confirmed; US federal agencies had to remediate it by May 9, 2026. CISA does not currently list it as used in ransomware campaigns. Palo Alto Networks has 16 vulnerabilities in the KEV catalog, 6 of them linked to ransomware.
All 16 known-exploited Palo Alto Networks vulnerabilities →Description
A buffer overflow vulnerability in the User-ID™ Authentication Portal (aka Captive Portal) service of Palo Alto Networks PAN-OS software allows an unauthenticated attacker to execute arbitrary code with root privileges on the PA-Series and VM-Series firewalls by sending specially crafted packets. The risk of this issue is greatly reduced if you secure access to the User-ID™ Authentication Portal per the best practice guidelines https://knowledgebase.paloaltonetworks.com/KCSArticleDetail by restricting access to only trusted internal IP addresses. Prisma Access, Cloud NGFW and Panorama appliances are not impacted by this vulnerability.
CVSS vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
CISA Known-Exploited Vulnerability
Product: Palo Alto Networks — PAN-OS
Name: Palo Alto Networks PAN-OS Out-of-bounds Write Vulnerability
Date added: 2026-05-06 · Due: 2026-05-09
Required action: Apply mitigations per vendor instructions, follow applicable BOD 22-01 guidance for cloud services, or discontinue use of the product if mitigations are unavailable. Until the vendor releases an official fix, the following workaround should be implemented: - Restrict User-ID Authentication Portal access to only trusted zones. - Disable User-ID Authentication Portal if not required. 5/13/2026: Palo Alto has released a variety of patches. If these are relevant to your environment, please apply the designated patch.