# CVE-2026-0300: PAN-OS: Unauthenticated user initiated Buffer Overflow Vulnerability in User-ID™ Authentication Portal

> CVE-2026-0300: PAN-OS: Unauthenticated user initiated Buffer Overflow Vulnerability in User-ID™ Authentication Portal. CVSS 9.8 (CVSS 3.1), in CISA KEV.

Canonical: https://rewindex.com/cve/CVE-2026-0300
Last updated: 2026-10-15T01:11:55Z

- Published: 2026-05-06 18:57 UTC · Updated: 2026-10-15 01:11 UTC · Assigner: palo\_alto
- CVSS: 9.8 (CVSS 3.1) · Severity: Critical · Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
- EPSS: 41.7%, 99th percentile (scored 2026-10-25)
- CISA KEV: yes, added 2026-05-06, federal due date 2026-05-09, ransomware use: Unknown
- CWE: 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.

## 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.

## Affected vendors and products

- Palo Alto Networks: Cloud NGFW
- Palo Alto Networks: PAN-OS
- Palo Alto Networks: Prisma Access
- Siemens: RUGGEDCOM APE1808

## References

- [CVE record on cve.org](https://www.cve.org/CVERecord?id=CVE-2026-0300)
- [NVD entry](https://nvd.nist.gov/vuln/detail/CVE-2026-0300)
- [https://security.paloaltonetworks.com/CVE-2026-0300](https://security.paloaltonetworks.com/CVE-2026-0300)

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_Sources: CVE records from the CVE Program (cve.org). CVE® is a registered trademark of The MITRE Corporation. (https://www.cve.org/) This product uses data from the NVD API but is not endorsed or certified by the NVD. (https://nvd.nist.gov/) Known Exploited Vulnerabilities catalog from CISA. (https://www.cisa.gov/known-exploited-vulnerabilities-catalog) EPSS scores from FIRST (Exploit Prediction Scoring System). (https://www.first.org/epss/)_


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Canonical: https://rewindex.com/cve/CVE-2026-0300 · Markdown: https://rewindex.com/cve/CVE-2026-0300.md · JSON: https://rewindex.com/api/v1/cves/CVE-2026-0300 · Data licensed CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/) · Generated 2026-10-26T03:13:16.819Z