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

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.

9.3 CRITICALEPSS 41.71%⚡ Known Exploited (CISA KEV)NVD: Analyzed

Last updated: 2026-10-26 19:10 UTC

OverviewCVSS details

9.3CRITICALCVSS 4.0

Score source: palo_alto (CNA)
NVD status: Analyzed
Published: May 6, 2026
Assigner: palo_alto

Affected

Cloud NGFW (Palo Alto Networks)

+2 more products →

Exploitation

Public exploit: None listed
CISA KEV: Listed · May 6, 2026
KEV due date: May 9, 2026
Ransomware use: Unknown
SSVC: Exploitation active · Automatable yes · Impact total

EPSS · FIRST, scored Nov 7

41.71%chance of exploitation in 30 days

Higher than 98.69% of CVEs

CVSS 4.0 · palo_alto (CNA)

9.3Critical

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

Attack vector: Network
Attack complexity: Low
Attack requirements: None
Privileges required: None
User interaction: None
Confidentiality impact: High
Integrity impact: High
Availability impact: High
Confidentiality (other systems): Low
Integrity (other systems): Low
Availability (other systems): None

CVSS 4.0 · palo_alto (CNA)

8.7High

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

Attack vector: Adjacent
Attack complexity: Low
Attack requirements: None
Privileges required: None
User interaction: None
Confidentiality impact: High
Integrity impact: High
Availability impact: High
Confidentiality (other systems): Low
Integrity (other systems): Low
Availability (other systems): None

CVSS 3.1 · NVD

9.8Critical

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

Attack vector: Network
Attack complexity: Low
Privileges required: None
User interaction: None
Scope: Unchanged
Confidentiality impact: High
Integrity impact: High
Availability impact: High

NVD status: Analyzed

Overview Affected Products References

NVD CVE.org

Overview

Severity

Score	Severity	Version	Vector String
9.3	CRITICAL	4.0palo_alto (CNA)	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
8.7	HIGH	4.0palo_alto (CNA)	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
9.8	CRITICAL	3.1NVD	CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

CISA required action

⚡ Known exploited · remediation due May 9, 2026

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.

Details

CVE ID: CVE-2026-0300
Status: Analyzed
Assigner (CNA): palo_alto
Published: May 6, 2026
Last modified: 2026-10-26 19:10 UTC
Weaknesses: CWE-787 · Out-of-bounds Write

Sources

Refreshed hourly from the sources above. Last fetched 2026-11-08 09:18 UTC.