Actively exploited in the wild
Palo Alto Networks PAN-OS Out-of-bounds Write Vulnerability
Palo Alto Networks - PAN-OS · Listed in the CISA KEV since 2026-05-06. This indicates confirmed attacks in production environments.
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.
CVE-2026-0300
CriticalCVSS 9.8KEVSummary
CVE-2026-0300 describes a buffer overflow vulnerability in the User-ID™ Authentication Portal service of Palo Alto Networks PAN-OS software, allowing an unauthenticated attacker to execute arbitrary code with root privileges on PA-Series and VM-Series firewalls by sending specially crafted packets.
Risk Assessment
The risk of this issue is greatly reduced if access to the User-ID™ Authentication Portal is secured according to best practice guidelines, restricting access to only trusted internal IP addresses.
Recommendation
It is recommended to secure access to the User-ID™ Authentication Portal by restricting it to trusted internal IP addresses in accordance with best practice guidelines.
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Original NVD description (English source)
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.
Vulnerability data from NVD (NIST) · CISA KEV · EPSS