CVE-2026-0300

CRITICAL severity · CVSS 9.8 · Out-of-bounds write · actively exploited (CISA KEV)

9.8CVSS CRITICAL ● exploited

🔴 Actively exploited in the wild (CISA Known Exploited Vulnerabilities). Added to KEV 2026-05-06. US federal agencies must patch by 2026-05-09.

Summary

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.

Impact & exploitability

Attack vectorNetwork

Attack complexityLow

Privileges requiredNone

User interactionNone

Confidentiality impactHigh

Integrity impactHigh

Availability impactHigh

Exploit probability (EPSS)5%

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Affected products we track (1)

Palo Alto PAN-OS

Recommendation

This vulnerability is being actively exploited in the wild — patch affected products urgently. Open any affected product above for its exact safe version.

CVE-2026-0300

Summary

Impact & exploitability

Affected products we track (1)

Recommendation

Additional information