CVE-2026-0300
Palo Alto Networks PAN-OS Out-of-bounds Write Vulnerability
Does this matter?
Known to be exploited in the wild (CISA KEV, CISA remediation deadline 9 May 2026). Treat as an emergency change: patch or isolate now, then hunt for prior compromise.
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.
- CVSS 4.0
- 9.3 CRITICALCVSS: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/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/M
- EPSS
- 31.72% probability · 98th percentile
- CISA KEV
- Listed 6 May 2026 · due 9 May 2026
- Weakness
- CWE-787
- Affected
- paloaltonetworks/pan-os · siemens/ruggedcom ape1808 firmware
- Source
- psirt@paloaltonetworks.com
CISA notes
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. https://security.paloaltonetworks.com/CVE-2026-0300 ; https://nvd.nist.gov/vuln/detail/CVE-2026-0300
References
- https://security.paloaltonetworks.com/CVE-2026-0300Mitigation, Vendor Advisory
- https://cert-portal.siemens.com/productcert/html/ssa-967325.htmlThird Party Advisory
- https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2026-0300US Government Resource
Source: NVD record, EPSS from FIRST.org, KEV from CISA. Refreshed daily.