Palo Alto Networks · PAN-OS
CVE-2026-0300
PAN-OS: Unauthenticated user initiated Buffer Overflow Vulnerability in User-ID™ Authentication Portal
What it is
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.
CISA: Palo Alto Networks PAN-OS contains an out-of-bounds write vulnerability in the User-ID Authentication Portal (aka Captive Portal) service that can allow an unauthenticated attacker to execute arbitrary code with root privileges on the PA-Series and VM-Series firewalls by sending specially crafted packets.
What to do
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.
Deadline for US federal agencies: May 9, 2026
More exploited flaws from Palo Alto Networks
| Added | Vulnerability | Product | Severity | Attack chance |
|---|---|---|---|---|
| Oct 14, 2026 | Code Injection | PAN-OS | High 8.6 | 1.7% |
| May 29, 2026 | Authentication Bypass | PAN-OS | High 7.8 | 95% |
| Feb 20, 2025 | File Read | PAN-OS | High 7.1 | 2.0% |
| Feb 18, 2025 | Authentication Bypass | PAN-OS | High 8.8 | 98% |
| Dec 30, 2024 | Malicious DNS Packet | PAN-OS | High 8.7 | 29% |
| Nov 18, 2024 | Management Interface Authentication Bypass | PAN-OS | Critical 9.3 | 99.8% |
| Nov 18, 2024 | Management Interface OS Command Injection | PAN-OS | Medium 6.9 | 94% |
| Apr 12, 2024 | Command Injection | PAN-OS | Critical 10.0 | >99.9% |
Sources: Known Exploited Vulnerabilities (CISA, public domain), CVE records (cve.org) and EPSS (FIRST). The chance of attacks is the EPSS estimate that someone will try to exploit the flaw in the next 30 days.