Palo Alto Networks PAN-OS Out-of-bounds Write Vulnerability

Technical Severity

CVSS v3.1 Metrics

CRITICAL

9.8 / 10

Minimal Risk Critical

Vector Specification

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Exploitation Likelihood

EPSS Prediction

31.76 %

Predictive Probability

Percentile Rank

98.1 th

Documented as more likely to be exploited than 98.1% of known CVEs.

Detection Date

May 06, 2026

Remediation Due

May 09, 2026

CISA Catalog Active

Threat Analysis

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.

Remediation Directive

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.

External Intelligence

https://security.paloaltonetworks.com/CVE-2026-0300

NVD

National Vulnerability Database

https://nvd.nist.gov/vuln/detail/CVE-2026-0300