---
title: "CVE-2026-0300: Palo Alto Networks PAN-OS Out-of-bounds Write Vulnerability"
url: https://erroneo.us/security/cve/CVE-2026-0300/
description: "CVE-2026-0300 (Palo Alto Networks PAN-OS): Exploited in the wild (CISA KEV). A buffer overflow vulnerability in the User-ID™ Authentication Portal (aka…"
type: vulnerability-record
section: "Security Digest"
date_published: 2026-05-06
date_modified: 2026-10-15
publisher: erroneo.us
author: erroneo.us Security Desk
cve: "CVE-2026-0300"
kev: true
cvss: 9.3
epss: 0.31725
license: All rights reserved. Quote with attribution and a link.
---

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

**Signal:** Exploited: patch now if you run it. CISA has confirmed exploitation in the wild. (Computed from CISA KEV, EPSS and CVSS; not an editorial verdict.)

## Should you act?

- Yes, if you run Palo Alto Networks PAN-OS. CISA added this CVE to its Known Exploited Vulnerabilities catalog on 2026-05-06, which means there is reliable evidence of exploitation in the wild. US federal agencies must remediate by 2026-05-09 ; treat that as the outer limit, not the target.
- EPSS 31.7% , percentile 98: FIRST’s model estimates a 31.7% chance of exploitation activity in the next 30 days, higher than 98% of all scored CVEs (very high). EPSS is a probability, not a verdict.
- Remotely reachable with no login and no user interaction. If the vulnerable service is exposed to the internet, prioritize it.

## What it is

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 (CVE record)

- Palo Alto Networks Cloud NGFW: see advisory
- Palo Alto Networks PAN-OS: 12.1.0 < 12.1.7, 11.2.0 < 11.2.12, 11.1.0 < 11.1.15, 10.2.0 < 10.2.18-h6
- Palo Alto Networks Prisma Access: see advisory

## Severity

- palo_alto CVSS 4.0: 9.3 `CVSS: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/AU:Y/R:U/V:C/RE:M/U:Red`
- palo_alto CVSS 4.0: 8.7 `CVSS:4.0/AV:A/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:L/SI:L/SA:N/E:A/AU:Y/R:U/V:C/RE:M/U:Red`

## Exploitation

- CISA KEV: added 2026-05-06; federal due date 2026-05-09. Known ransomware use: Unknown.
- 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.
- CISA SSVC assessment: exploitation active , automatable yes , technical impact total .
- FIRST EPSS (model of 2026-10-21): 31.72% probability of exploitation activity in the next 30 days; percentile 98.

## Sources

- [security.paloaltonetworks.com](https://security.paloaltonetworks.com/CVE-2026-0300)
- [CVE.org record CVE-2026-0300](https://www.cve.org/CVERecord?id=CVE-2026-0300)
- [NVD entry CVE-2026-0300](https://nvd.nist.gov/vuln/detail/CVE-2026-0300)
- [CISA Known Exploited Vulnerabilities catalog entry](https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2026-0300)
- [cert-portal.siemens.com](https://cert-portal.siemens.com/productcert/html/ssa-967325.html)

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Source page: https://erroneo.us/security/cve/CVE-2026-0300/ · Security Digest: https://erroneo.us/security/ · More: https://erroneo.us/llms.txt