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CVE-2026-0300: Palo Alto Networks PAN-OS Out-of-bounds Write Vulnerability

• Severity: critical (CVSS 9.8 v3.1)
• Exploited in the wild: yes — in CISA KEV since 2026-05-06
• EPSS: 41.7% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2026-05-06 · updated 2026-10-26
• Weakness: CWE-787

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

• Palo Alto Networks PAN-OS: 10.2.0, 10.2.1, 10.2.2, 10.2.3, 10.2.4, 10.2.5 (+156)
• Siemens Ruggedcom Ape1808 Firmware: all versions

References

• https://security.paloaltonetworks.com/CVE-2026-0300
• https://cert-portal.siemens.com/productcert/html/ssa-967325.html
• https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2026-0300

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