The U.S. Cybersecurity and Infrastructure Security Agency (CISA) added a flaw in the Palo Alto Networks PAN-OS, tracked as CVE-2026-0300 (CVSS score of 9.3), to its Known Exploited Vulnerabilities (KEV) catalog.
The flaw is a buffer overflow that allows unauthenticated remote code execution, especially when the User-ID portal is exposed to the internet.
“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.” reads the advisory published by Palo Alto Networks. “The risk of this issue is greatly reduced if you secure access to the User-ID™ Authentication Portal per the best practice guidelines by restricting access to only trusted internal IP addresses.”
This week, Palo Alto Networks has warned that the critical PAN-OS vulnerability CVE-2026-0300 is actively exploited in the wild.
Below is the list of impacted products:
| Versions | Affected | Unaffected |
|---|---|---|
| Cloud NGFW | None | All |
| PAN-OS 12.1 | < 12.1.4-h5 < 12.1.7 | >= 12.1.4-h5 (ETA: 05/13) >= 12.1.7 (ETA: 05/28) |
| PAN-OS 11.2 | < 11.2.4-h17 < 11.2.7-h13 < 11.2.10-h6 < 11.2.12 | >= 11.2.4-h17 (ETA: 05/28) >= 11.2.7-h13 (ETA: 05/13) >= 11.2.10-h6 (ETA: 05/13) >= 11.2.12 (ETA: 05/28) |
| PAN-OS 11.1 | < 11.1.4-h33 < 11.1.6-h32 < 11.1.7-h6 < 11.1.10-h25 < 11.1.13-h5 < 11.1.15 | >= 11.1.4-h33 (ETA: 05/13) >= 11.1.6-h32 (ETA: 05/13) >= 11.1.7-h6 (ETA: 05/28) >= 11.1.10-h25 (ETA: 05/13) >= 11.1.13-h5 (ETA: 05/13) >= 11.1.15 (ETA: 05/28) |
| PAN-OS 10.2 | < 10.2.7-h34 < 10.2.10-h36 < 10.2.13-h21 < 10.2.16-h7 < 10.2.18-h6 | >= 10.2.7-h34 (ETA: 05/28) >= 10.2.10-h36 (ETA: 05/13) >= 10.2.13-h21 (ETA: 05/28) >= 10.2.16-h7 (ETA: 05/28) >= 10.2.18-h6 (ETA: 05/13) |
| Prisma Access | None | All |
The cybersecurity vendor states that the issue doesn’t impact Prisma Access, Cloud NGFW and Panorama appliances.
Palo Alto Networks says the flaw is being exploited in a limited way, mainly against systems where the User-ID Authentication Portal is exposed to the public internet.
The flaw remains unpatched, with fixes expected from May 13, 2026. It affects PA-Series and VM-Series firewalls using the User-ID Authentication Portal. Palo Alto Networks notes risk is much lower for organizations that follow best practices, like limiting access to trusted internal networks only.
“Limited exploitation has been observed targeting Palo Alto Networks User-ID™ Authentication Portals that are exposed to untrusted IP addresses and/or the public internet.” concludes the advisory. “Customers following standard security best practices, such as restricting sensitive portals to trusted internal networks are at a greatly reduced risk.”
According to Binding Operational Directive (BOD) 22-01: Reducing the Significant Risk of Known Exploited Vulnerabilities, FCEB agencies have to address the identified vulnerabilities by the due date to protect their networks against attacks exploiting the flaws in the catalog.
Experts also recommend that private organizations review the Catalog and address the vulnerabilities in their infrastructure.
CISA orders federal agencies to fix the vulnerability by May 9, 2026.
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