CVE-2026-0300

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

Actively exploited (CISA KEV) Critical 9.8 CVSS 3.1

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.

Description as published by the source, in English.

Key facts

Published: 2026-05-06
Last modified: 2026-06-17
Assigned by: psirt@paloaltonetworks.com
CVSS vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Scored by: nvd@nist.gov (NVD Primary)
Probability of exploitation: 32.1 % higher than 98 % of all known vulnerabilities
EPSS, next 30 days, model v2026.06.15
Fix available: Not registered in the sources

Actively exploited

CISA added this vulnerability to the Known Exploited Vulnerabilities catalogue on 2026-05-06, with a remediation deadline of 2026-05-09 for US federal agencies.

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 products

Vendor	Product	Versions	Status
Paloaltonetworks	Pa-1410	all versions listed	Not affected
Paloaltonetworks	Pa-1420	all versions listed	Not affected
Paloaltonetworks	Pa-3410	all versions listed	Not affected
Paloaltonetworks	Pa-3420	all versions listed	Not affected
Paloaltonetworks	Pa-3430	all versions listed	Not affected
Paloaltonetworks	Pa-3440	all versions listed	Not affected
Paloaltonetworks	Pa-410	all versions listed	Not affected
Paloaltonetworks	Pa-410r	all versions listed	Not affected
Paloaltonetworks	Pa-410r-5g	all versions listed	Not affected
Paloaltonetworks	Pa-415	all versions listed	Not affected
Paloaltonetworks	Pa-415-5g	all versions listed	Not affected
Paloaltonetworks	Pa-440	all versions listed	Not affected
Paloaltonetworks	Pa-445	all versions listed	Not affected
Paloaltonetworks	Pa-450	all versions listed	Not affected
Paloaltonetworks	Pa-450r	all versions listed	Not affected
Paloaltonetworks	Pa-450r-5g	all versions listed	Not affected
Paloaltonetworks	Pa-455	all versions listed	Not affected
Paloaltonetworks	Pa-455-5g	all versions listed	Not affected
Paloaltonetworks	Pa-455r-5g	all versions listed	Not affected
Paloaltonetworks	Pa-460	all versions listed	Not affected
Paloaltonetworks	Pa-501	all versions listed	Not affected
Paloaltonetworks	Pa-505	all versions listed	Not affected
Paloaltonetworks	Pa-510	all versions listed	Not affected
Paloaltonetworks	Pa-520	all versions listed	Not affected
Paloaltonetworks	Pa-540	all versions listed	Not affected
Paloaltonetworks	Pa-5410	all versions listed	Not affected
Paloaltonetworks	Pa-5420	all versions listed	Not affected
Paloaltonetworks	Pa-5430	all versions listed	Not affected
Paloaltonetworks	Pa-5440	all versions listed	Not affected
Paloaltonetworks	Pa-5445	all versions listed	Not affected
Paloaltonetworks	Pa-545-poe	all versions listed	Not affected
Paloaltonetworks	Pa-5450	all versions listed	Not affected
Paloaltonetworks	Pa-550	all versions listed	Not affected
Paloaltonetworks	Pa-5540	all versions listed	Not affected
Paloaltonetworks	Pa-555-poe	all versions listed	Not affected
Paloaltonetworks	Pa-5550	all versions listed	Not affected
Paloaltonetworks	Pa-5560	all versions listed	Not affected
Paloaltonetworks	Pa-5570	all versions listed	Not affected
Paloaltonetworks	Pa-5580	all versions listed	Not affected
Paloaltonetworks	Pa-560	all versions listed	Not affected
Paloaltonetworks	Pa-7500	all versions listed	Not affected
Paloaltonetworks	Pa-7500-dpc-a	all versions listed	Not affected
Paloaltonetworks	Pan-os	10.2.0	Affected
Paloaltonetworks	Pan-os	10.2.1	Affected
Paloaltonetworks	Pan-os	10.2.10	Affected
Paloaltonetworks	Pan-os	10.2.11	Affected
Paloaltonetworks	Pan-os	10.2.12	Affected
Paloaltonetworks	Pan-os	10.2.13	Affected
Paloaltonetworks	Pan-os	10.2.14	Affected
Paloaltonetworks	Pan-os	10.2.15	Affected
Paloaltonetworks	Pan-os	10.2.16	Affected
Paloaltonetworks	Pan-os	10.2.17	Affected
Paloaltonetworks	Pan-os	10.2.18	Affected
Paloaltonetworks	Pan-os	10.2.2	Affected
Paloaltonetworks	Pan-os	10.2.3	Affected
Paloaltonetworks	Pan-os	10.2.4	Affected
Paloaltonetworks	Pan-os	10.2.5	Affected
Paloaltonetworks	Pan-os	10.2.6	Affected
Paloaltonetworks	Pan-os	10.2.7	Affected
Paloaltonetworks	Pan-os	10.2.8	Affected

Weakness type

CWE-787: Out-of-bounds Write
The product writes data past the end, or before the beginning, of the intended buffer.

References

https://security.paloaltonetworks.com/CVE-2026-0300 Mitigation, Vendor Advisory
https://cert-portal.siemens.com/productcert/html/ssa-967325.html Third Party Advisory
https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2026-0300 US Government Resource

Related at Berigo

Articles

Critical PAN-OS flaw exploited against exposed firewalls Mentions this CVE 2026-05-06
CVE-2026-0300 in PAN-OS carries CVSS 9.3, can grant root without authentication, and is already under limited exploitation.
Palo Alto releases a fix for a PAN-OS vulnerability Same product 2026-07-08
CVE-2026-0288 can, under specific conditions, let an authenticated attacker affect confidentiality and integrity in PAN-OS.
Unit 42: language models invent domains that attackers then register Same product 2026-06-30
Unit 42 found around 250,000 unregistered domains invented by language models, and at least one case where an attacker registered one and set up phis…
Palo Alto GlobalProtect vulnerability exploited in the wild Same product 2026-05-29
CVE-2026-0257 has been added to CISA's Known Exploited Vulnerabilities catalog, allowing an unauthorised VPN connection in certain PAN-OS configurati…

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Sources and freshness

CVE

What it is: A reference number naming one specific vulnerability, for example CVE-2024-9474.
What it tells you: Which vulnerability we are talking about, and in which product.
What it does NOT tell you: Nothing about how serious it is, whether anyone is exploiting it, or whether it concerns you.
Why it matters: Without a shared number, vendor, authority and tooling cannot discuss the same flaw.
Used with the others: The number is the key. NVD, KEV and EPSS all describe the same CVE.

NVD CWE CISA KEV EPSS

How to read this together

No single value should be used on its own. A high CVSS score does not mean a vulnerability is being exploited, and a low one does not mean it is harmless. The four sources answer four different questions.

CVE names the specific vulnerability.
NVD adds severity and technical detail about it.
CWE describes the type of mistake behind it.
CISA KEV shows that it is already being exploited.
EPSS estimates how likely exploitation is soon.

The order that decides what is urgent

Do you actually have the product?
Is the version you run affected?
Is it listed in CISA KEV?
Does it have a high EPSS score?
Is the system reachable from the internet or from others?
How important is the system to the business?
Are there compensating controls already in place?

The first two questions are not about the vulnerability at all. They are about you, and they remove most of the list before you start.

A short example

Fix this week

CVSS 6,5 (medium)

In CISA KEV: yes
EPSS: 94 per cent
A firewall facing the internet

Can be scheduled

CVSS 9,8 (critical)

In CISA KEV: no
EPSS: 0,04 per cent
A test server with no internet access

Sorted by CVSS alone, the one on the right comes first. It is the more serious flaw in theory. But the one on the left is being used against real organisations right now, and it sits where an attacker can reach it. That is the one to fix first.

The critical one still has to be fixed. It just does not have to be fixed today.

This product uses the NVD API but is not endorsed or certified by the NVD. CVE and the CVE logo are registered trademarks of The MITRE Corporation; CVE records are used under the CVE Terms of Use. CWE is a trademark of The MITRE Corporation, used per the CWE Terms of Use. KEV data from CISA (CC0). Exploitation probability from EPSS, a FIRST.org project. Open-source package data from OSV and the GitHub Advisory Database (CC-BY 4.0).

Scores and vectors are shown as published by the sources. The ordering of results is Berigo's own editorial assessment, described on the search page, and is not NVD data. An empty result never means a system is safe.