CVE entry · CVE-2026-0300
CVE-2026-0300: Palo Alto Networks PAN-OS Out-of-bounds Write Vulnerability
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.
- Actively exploited: added to CISA’s KEV catalog on May 6, 2026.
- Use by ransomware: not established so far.
- Remediation deadline for US federal agencies: May 9, 2026.
Description from CISA’s KEV catalog.
What to do
- Check whether your estate includes Palo Alto Networks PAN-OS, including internet-facing devices.
- Apply the vendor’s patch or mitigations (references below). Failing that, isolate the product or stop using it, as CISA requires of US federal agencies.
- An exploited vulnerability has often been used before it was fixed: look for signs of compromise, especially on internet-facing devices.
References
- Vendor advisory or reference cited by CISA (security.paloaltonetworks.com)
- NVD entry (NIST)
- CISA KEV catalog