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CVE-2026-0300: Palo Alto Networks PAN-OS Out of Bounds Write (CVSS 9.3)

CVE-2026-0300 is a critical severity out of bounds write in Palo Alto Networks PAN-OS with a CVSS score of 9.3. It is listed in the CISA Known Exploited Vulnerabilities catalog, so treat it as an active threat and patch immediately.

Last updated: Jun 17, 2026

Quick answer

Direct answer

CVE-2026-0300 is a critical severity out of bounds write in Palo Alto Networks PAN-OS with a CVSS score of 9.3. It is listed in the CISA Known Exploited Vulnerabilities catalog, so treat it as an active threat and patch immediately.

Risk scores

CVSS base score
9.3CRITICAL
EPSS probability
31.72%
Higher than 98 percent of all CVEs
CISA KEV
Exploited Yes
Added May 6, 2026
CVSS metricWhat it means
Attack vector (AV:N)Network: reachable remotely
Attack complexity (AC:L)Low complexity
Attack requirements (AT:N)No attack requirements
Privileges required (PR:N)No privileges required
User interaction (UI:N)No user interaction
Confidentiality (VC:H)High confidentiality impact
Integrity (VI:H)High integrity impact
Availability (VA:H)High availability impact

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/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:Y/R:U/V:C/RE:M/U:Red

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.

About Palo Alto Networks PAN-OS

CVE-2026-0300 affects Palo Alto Networks PAN-OS, a product from Palo Alto Networks. Before acting, confirm where Palo Alto Networks PAN-OS runs in your estate, who owns it and whether it is reachable from the internet, because exposure decides real risk more than the score alone.

What the flaw is

In plain terms: 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.

The weakness class is Out of Bounds Write. The program writes past the end of a buffer, a common path to code execution.

Based on its CVSS vector, the flaw can be reached over the network, needs no login, and needs no user interaction. It is listed in the CISA Known Exploited Vulnerabilities catalog, so treat it as an active threat and patch immediately.

Affected versions and timeline

FieldDetail
ProductPalo Alto Networks PAN-OS
Affected versionsPan-Os 10.2.0; Pan-Os 10.2.1; Pan-Os 10.2.2; Pan-Os 10.2.3; Pan-Os 10.2.4; Pan-Os 10.2.5; Pan-Os 10.2.6; Pan-Os 10.2.7; Pan-Os 10.2.8; Pan-Os 10.2.9; Pan-Os 10.2.10; Pan-Os 10.2.11
PublishedMay 6, 2026
Last modifiedJun 17, 2026
Added to CISA KEVMay 6, 2026
Assigning CNApsirt@paloaltonetworks.com

How to detect it

  • Inventory every instance of Palo Alto Networks PAN-OS and record the running version against the affected range above.
  • Check external attack surface scans for internet facing instances of the component.
  • Review logs on affected systems for unusual requests, errors or new processes around the vulnerable function.
  • Confirm with an authenticated vulnerability scan once your scanner has a check for this CVE.

How to fix it

  • Apply the fixed version of Palo Alto Networks PAN-OS named in the vendor advisory.
  • If patching must wait, restrict network access to the affected service and put it behind authentication or a web application firewall rule.
  • Rescan after the change to prove the exposure is gone, then close the ticket.

CTEM action plan

CTEM stageWhat to do for this CVE
ScopeAdd every business service that depends on Palo Alto Networks PAN-OS to the current CTEM cycle.
DiscoverFind all instances, including shadow and cloud deployments, and record versions and exposure.
PrioritizeKnown exploited, so top priority.
ValidateConfirm the flaw is reachable and exploitable in your environment and that compensating controls work.
MobilizeAssign the fix to the asset owner with a due date matched to the priority, then verify closure.

CWE References

Technical References

Frequently asked questions

CVE-2026-0300 is a critical severity out of bounds write in Palo Alto Networks PAN-OS with a CVSS score of 9.3. It is listed in the CISA Known Exploited Vulnerabilities catalog, so treat it as an active threat and patch immediately.

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