Actively exploited · Published May 6, 2026 · Assigned by palo_alto
CVE-2026-0300PAN-OS: Unauthenticated user initiated Buffer Overflow Vulnerability in User-ID™ Authentication Portal
Critical 9.3 Exploited
In plain English
A critical-severity out-of-bounds write in Cloud NGFW from Palo Alto Networks. Attackers are actively exploiting it in the wild (listed by CISA on May 6, 2026). The chance it is exploited in the next 30 days is estimated at 41.7% (higher than 99% of all known vulnerabilities). Ready-made attack tooling exists: public proof-of-concept code. 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.
CISA guidance
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.
Federal agencies must remediate by May 9, 2026.
Official 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.
Affected products (as reported)
| Vendor | Product | Versions |
|---|---|---|
| Palo Alto Networks | Cloud NGFW | see references |
| Palo Alto Networks | PAN-OS | 12.1.0 – before 12.1.711.2.0 – before 11.2.1211.1.0 – before 11.1.1510.2.0 – before 10.2.18-h6 |
| Palo Alto Networks | Prisma Access | see references |
Weakness: CWE-787 · Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:L/SI:L/SA:N/E:A/AU:Y/R:U/V:C/RE:M/U:Red