Home/CVE/Palo Alto Networks PAN-OS Out-of-bounds Write Vulnerability
CVE

CVE-2026-0300

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

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.

CRITICAL · CVSS 9.8 ⚠ CISA KEV EPSS 0.04536
Act now
  • Listed on CISA KEV (known exploited in the wild)
  • SSVC exploitation status: active
  • SSVC automatable: yes - attacks can be scripted at scale
  • CVSS base score ≥ 7.0
Sigma rules0 YARA rules0
⬢

Required Remediation

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.

⬡

Weakness Classification

CWE-787Out-of-bounds Write
▤

Affected Products & Versions

1
paloaltonetworks pan-osall versions
▣

Scoring & Timeline

9.8
CRITICAL · CVSS v3.1 · psirt@paloaltonetworks.com
View on NVD
Attack Vector
Network Adjacent Local Physical
Attack Complexity
Low High
Privileges Required
None Low High
User Interaction
None Required
Scope
Unchanged Changed
Confidentiality
None Low High
Integrity
None Low High
Availability
None Low High
Published to NVD06 May 2026 · 07:16 PM
CVSS VectorCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
SSVC triage · cisa-vulnrichment
Exploitation
active
Automatable
yes
Technical impact
total
SSVC asks the questions that actually drive patch urgency: is it being exploited, can attacks be automated, and how total is the impact.
⚑

Vendor Advisories

4
cisa-aa-advisoriesicsa-26-139-02
siemens-csafSSA-967325
cisaKEV-CVE-2026-0300
cisa-csafcisa-csaf-csaf_files-OT-white-2026-icsa-26-139-02
🔗

References & Sources

2
Source URLs (vendor pages, mailing lists, write-ups). Exploit/PoC links are in their own section above to avoid duplication.
https://cert-portal.siemens.com/productcert/html/ssa-967325.htmlThird Party Advisory
https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2026-0300US Government Resource
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