---
id: "CVE-2026-0300"
kind: "vulnerability"
aliases: ["CVE-2026-0300"]
title: "paloaltonetworks pan-os: A buffer overflow vulnerability in the User-ID\u2122 Authentication Portal (aka Captive Portal) service of Palo Alto\u2026"
severity: "critical"
cvss: 9.8
epss: null
exploited: true
status: "open"
category: "infrastructure"
products: [{"name": "Palo Alto Networks PAN-OS", "fixed": [], "affected": "", "ecosystem": "vendor"}, {"name": "paloaltonetworks pan-os", "fixed": [], "affected": "= 10.2.0", "ecosystem": "vendor"}, {"name": "paloaltonetworks pan-os", "fixed": [], "affected": "= 10.2.1", "ecosystem": "vendor"}, {"name": "paloaltonetworks pan-os", "fixed": [], "affected": "= 10.2.2", "ecosystem": "vendor"}, {"name": "paloaltonetworks pan-os", "fixed": [], "affected": "= 10.2.3", "ecosystem": "vendor"}, {"name": "paloaltonetworks pan-os", "fixed": [], "affected": "= 10.2.4", "ecosystem": "vendor"}, {"name": "paloaltonetworks pan-os", "fixed": [], "affected": "= 10.2.5", "ecosystem": "vendor"}, {"name": "paloaltonetworks pan-os", "fixed": [], "affected": "= 10.2.6", "ecosystem": "vendor"}, {"name": "paloaltonetworks pan-os", "fixed": [], "affected": "= 10.2.7", "ecosystem": "vendor"}, {"name": "paloaltonetworks pan-os", "fixed": [], "affected": "= 10.2.8", "ecosystem": "vendor"}, {"name": "paloaltonetworks pan-os", "fixed": [], "affected": "= 10.2.9", "ecosystem": "vendor"}, {"name": "paloaltonetworks pan-os", "fixed": [], "affected": "= 10.2.10", "ecosystem": "vendor"}, {"name": "paloaltonetworks pan-os", "fixed": [], "affected": "= 10.2.11", "ecosystem": "vendor"}, {"name": "paloaltonetworks pan-os", "fixed": [], "affected": "= 10.2.12", "ecosystem": "vendor"}, {"name": "paloaltonetworks pan-os", "fixed": [], "affected": "= 10.2.13", "ecosystem": "vendor"}, {"name": "paloaltonetworks pan-os", "fixed": [], "affected": "= 10.2.14", "ecosystem": "vendor"}, {"name": "paloaltonetworks pan-os", "fixed": [], "affected": "= 10.2.15", "ecosystem": "vendor"}, {"name": "paloaltonetworks pan-os", "fixed": [], "affected": "= 10.2.16", "ecosystem": "vendor"}, {"name": "paloaltonetworks pan-os", "fixed": [], "affected": "= 10.2.17", "ecosystem": "vendor"}, {"name": "paloaltonetworks pan-os", "fixed": [], "affected": "= 10.2.18", "ecosystem": "vendor"}, {"name": "paloaltonetworks pan-os", "fixed": [], "affected": "= 11.1.0", "ecosystem": "vendor"}, {"name": "paloaltonetworks pan-os", "fixed": [], "affected": "= 11.1.1", "ecosystem": "vendor"}, {"name": "paloaltonetworks pan-os", "fixed": [], "affected": "= 11.1.2", "ecosystem": "vendor"}, {"name": "paloaltonetworks pan-os", "fixed": [], "affected": "= 11.1.3", "ecosystem": "vendor"}, {"name": "paloaltonetworks pan-os", "fixed": [], "affected": "= 11.1.4", "ecosystem": "vendor"}, {"name": "paloaltonetworks pan-os", "fixed": [], "affected": "= 11.1.5", "ecosystem": "vendor"}, {"name": "paloaltonetworks pan-os", "fixed": [], "affected": "= 11.1.6", "ecosystem": "vendor"}, {"name": "paloaltonetworks pan-os", "fixed": [], "affected": "= 11.1.7", "ecosystem": "vendor"}, {"name": "paloaltonetworks pan-os", "fixed": [], "affected": "= 11.1.8", "ecosystem": "vendor"}, {"name": "paloaltonetworks pan-os", "fixed": [], "affected": "= 11.1.9", "ecosystem": "vendor"}, {"name": "paloaltonetworks pan-os", "fixed": [], "affected": "= 11.1.10", "ecosystem": "vendor"}, {"name": "paloaltonetworks pan-os", "fixed": [], "affected": "= 11.1.11", "ecosystem": "vendor"}, {"name": "paloaltonetworks pan-os", "fixed": [], "affected": "= 11.1.12", "ecosystem": "vendor"}, {"name": "paloaltonetworks pan-os", "fixed": [], "affected": "= 11.1.13", "ecosystem": "vendor"}, {"name": "paloaltonetworks pan-os", "fixed": [], "affected": "= 11.1.14", "ecosystem": "vendor"}, {"name": "paloaltonetworks pan-os", "fixed": [], "affected": "= 11.2.0", "ecosystem": "vendor"}, {"name": "paloaltonetworks pan-os", "fixed": [], "affected": "= 11.2.1", "ecosystem": "vendor"}, {"name": "paloaltonetworks pan-os", "fixed": [], "affected": "= 11.2.2", "ecosystem": "vendor"}, {"name": "paloaltonetworks pan-os", "fixed": [], "affected": "= 11.2.3", "ecosystem": "vendor"}, {"name": "paloaltonetworks pan-os", "fixed": [], "affected": "= 11.2.4", "ecosystem": "vendor"}, {"name": "paloaltonetworks pan-os", "fixed": [], "affected": "= 11.2.5", "ecosystem": "vendor"}]
ecosystems: ["vendor"]
tags: ["exploited", "firewall", "infrastructure", "pa-series", "palo-alto-networks", "pan-os", "vm-series"]
not_affected_if: ["no-untrusted-zone-access", "portal-disabled"]
published_at: "2026-05-06T00:00:00+00:00"
first_seen_at: "2026-10-23T19:11:51+00:00"
updated_at: "2026-10-23T23:44:51+00:00"
sources: [{"source": "kev", "url": "https://www.cisa.gov/known-exploited-vulnerabilities-catalog?search_api_fulltext=CVE-2026-0300", "first_seen_at": "2026-10-23T19:11:51+00:00"}, {"source": "nvd", "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-0300", "first_seen_at": "2026-10-23T23:44:51+00:00"}]
---

# paloaltonetworks pan-os: A buffer overflow vulnerability in the User-ID™ Authentication Portal (aka Captive Portal) service of Palo Alto…

Palo Alto PAN-OS has an out-of-bounds write in the User-ID Authentication Portal (Captive Portal) service on PA-Series and VM-Series firewalls. An unauthenticated attacker can send crafted packets to execute arbitrary code as root on the firewall.

_Summary, check and fix written by a model from the sources; labelled as such._

## Affected

- vendor:Palo Alto Networks PAN-OS affected ? fixed ?
- vendor:paloaltonetworks pan-os affected = 10.2.0 fixed ?
- vendor:paloaltonetworks pan-os affected = 10.2.1 fixed ?
- vendor:paloaltonetworks pan-os affected = 10.2.2 fixed ?
- vendor:paloaltonetworks pan-os affected = 10.2.3 fixed ?
- vendor:paloaltonetworks pan-os affected = 10.2.4 fixed ?
- vendor:paloaltonetworks pan-os affected = 10.2.5 fixed ?
- vendor:paloaltonetworks pan-os affected = 10.2.6 fixed ?
- vendor:paloaltonetworks pan-os affected = 10.2.7 fixed ?
- vendor:paloaltonetworks pan-os affected = 10.2.8 fixed ?
- vendor:paloaltonetworks pan-os affected = 10.2.9 fixed ?
- vendor:paloaltonetworks pan-os affected = 10.2.10 fixed ?
- vendor:paloaltonetworks pan-os affected = 10.2.11 fixed ?
- vendor:paloaltonetworks pan-os affected = 10.2.12 fixed ?
- vendor:paloaltonetworks pan-os affected = 10.2.13 fixed ?
- vendor:paloaltonetworks pan-os affected = 10.2.14 fixed ?
- vendor:paloaltonetworks pan-os affected = 10.2.15 fixed ?
- vendor:paloaltonetworks pan-os affected = 10.2.16 fixed ?
- vendor:paloaltonetworks pan-os affected = 10.2.17 fixed ?
- vendor:paloaltonetworks pan-os affected = 10.2.18 fixed ?
- vendor:paloaltonetworks pan-os affected = 11.1.0 fixed ?
- vendor:paloaltonetworks pan-os affected = 11.1.1 fixed ?
- vendor:paloaltonetworks pan-os affected = 11.1.2 fixed ?
- vendor:paloaltonetworks pan-os affected = 11.1.3 fixed ?
- vendor:paloaltonetworks pan-os affected = 11.1.4 fixed ?
- vendor:paloaltonetworks pan-os affected = 11.1.5 fixed ?
- vendor:paloaltonetworks pan-os affected = 11.1.6 fixed ?
- vendor:paloaltonetworks pan-os affected = 11.1.7 fixed ?
- vendor:paloaltonetworks pan-os affected = 11.1.8 fixed ?
- vendor:paloaltonetworks pan-os affected = 11.1.9 fixed ?
- vendor:paloaltonetworks pan-os affected = 11.1.10 fixed ?
- vendor:paloaltonetworks pan-os affected = 11.1.11 fixed ?
- vendor:paloaltonetworks pan-os affected = 11.1.12 fixed ?
- vendor:paloaltonetworks pan-os affected = 11.1.13 fixed ?
- vendor:paloaltonetworks pan-os affected = 11.1.14 fixed ?
- vendor:paloaltonetworks pan-os affected = 11.2.0 fixed ?
- vendor:paloaltonetworks pan-os affected = 11.2.1 fixed ?
- vendor:paloaltonetworks pan-os affected = 11.2.2 fixed ?
- vendor:paloaltonetworks pan-os affected = 11.2.3 fixed ?
- vendor:paloaltonetworks pan-os affected = 11.2.4 fixed ?
- vendor:paloaltonetworks pan-os affected = 11.2.5 fixed ?

## How to check

Check whether the User-ID Authentication Portal (Captive Portal) is enabled on the firewall and which zones can reach it.

## Fix

Restrict User-ID Authentication Portal access to trusted zones only, or disable it if not required, then apply the PAN-OS patch Palo Alto designated for your version.

## Timeline

- 2026-10-23T19:11:51+00:00 kev https://www.cisa.gov/known-exploited-vulnerabilities-catalog?search_api_fulltext=CVE-2026-0300
- 2026-10-23T23:44:51+00:00 nvd https://nvd.nist.gov/vuln/detail/CVE-2026-0300

## From the sources

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.

CISA required action: 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.

---

_Free to read at a human pace. An API with keys and an MCP server are in preparation; early access: hello@infrastack.ai_