criticalCISA KEVCVE-2026-0300

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

Palo Alto Networks PAN-OS contains an out-of-bounds write vulnerability in the User-ID Authentication Portal (aka Captive Portal) service that can allow an unauthenticated attacker to execute arbitrary code with root privileges on the PA-Series and VM-Series firewalls by sending specially crafted packets.

ProductPAN-OS

CVSS9.3

EPSS0.36157

UpdatedJuly 9, 2026

Quick answer

Palo Alto Networks PAN-OS should be reviewed and updated if it matches the affected versions. The recommended fix is to apply the vendor-supported patched version or the mitigation steps below, then retest the public website with Fixnx.

Who is affected

Affected versions

10.2.0
10.2.1
10.2.2
10.2.3
10.2.4
10.2.5
10.2.6
10.2.7
10.2.8
10.2.9
10.2.10
10.2.11
10.2.12
10.2.13
10.2.14
10.2.15
10.2.16
10.2.17
10.2.18
11.1.0
11.1.1
11.1.2
11.1.3
11.1.4
11.1.5
11.1.6
11.1.7
11.1.8
11.1.9
11.1.10
11.1.11
11.1.12
11.1.13
11.1.14
11.2.0
11.2.1
11.2.2
11.2.3
11.2.4
11.2.5
11.2.6
11.2.7
11.2.8
11.2.9
11.2.10
11.2.11
12.1.2
12.1.3
12.1.4
12.1.5
12.1.6
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Fixed versions

Apply the latest vendor-supported patched version.

How to fix it

CVE-2026-0300 is a critical PAN-OS buffer overflow in the User-ID Authentication Portal service. Palo Alto Networks reports exploitation against portals exposed to untrusted networks, so patching and exposure reduction should happen together. Upgrade PAN-OS to the fixed release for the installed branch, restrict or disable the Authentication Portal, and review firewall logs for attempted exploitation.

Identify PA-Series and VM-Series firewalls with User-ID Authentication Portal enabled.
Upgrade PAN-OS to the fixed release for the installed branch, or to a supported newer branch with the fix.
Restrict User-ID Authentication Portal access to trusted internal zones and trusted source IP ranges only.
Disable User-ID Authentication Portal if it is not required for the environment.
Disable response pages on interfaces where untrusted or internet traffic can ingress unless explicitly required by the vendor guidance.
Enable the relevant Threat Prevention content and signatures where licensed and supported.
Review traffic, threat, system, and configuration logs for suspicious requests to the Authentication Portal.

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Verify the fix

Confirm PAN-OS reports a fixed version for the deployed branch.
Verify User-ID Authentication Portal is not reachable from the public internet or untrusted zones.
Confirm response page and interface management profiles match the vendor mitigation guidance.
Review firewall logs for blocked or suspicious exploit attempts after mitigation.
Run a Fixnx scan and external exposure test against public firewall-facing services.

Related categories

pan-os

Trusted references

CISA KEV entryCISA KEV Source advisoryCISA KEV Source advisoryCISA KEV

FAQ

What is affected by CVE-2026-0300?

Palo Alto Networks PAN-OS should be checked against the vendor advisory and trusted references linked on this page.

What should I fix first?

Start with internet-facing sites, admin panels, login flows, plugins, themes, modules, packages, and systems that process user-controlled input or sensitive data.

How do I confirm the fix worked?

Apply the patched version or mitigation, clear caches where relevant, retest the affected workflow, and run a new Fixnx scan to verify public website exposure signals.

Why can this risk appear in multiple categories?

A vulnerability can belong to more than one platform or ecosystem. Fixnx keeps one canonical risk page while also listing it in every relevant category.