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CVE Record

CVE-2026-0300: PAN-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.

CriticalCVSS 9.3Known exploitedUpdated
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Glexia's TakeAutomated analysiscritical

Security readout for executives and security teams

Plain-English summary

CVE-2026-0300 is a critical flaw in Palo Alto Networks PAN-OS User-ID Authentication Portal. An unauthenticated attacker can potentially take over affected PA-Series or VM-Series firewalls with root-level code execution. CISA lists it in KEV, so treat internet or broadly reachable portals as urgent.

Executive priority

Emergency priority for any reachable affected firewall. This is an actively exploited, unauthenticated path to root control of security infrastructure. Assign immediate ownership to firewall and incident response teams, reduce exposure now, and follow vendor upgrade guidance as soon as confirmed.

Technical view

The issue is a CWE-787 buffer overflow in the PAN-OS User-ID Authentication Portal, also called Captive Portal. Specially crafted packets can trigger unauthenticated arbitrary code execution with root privileges. Prisma Access, Cloud NGFW, and Panorama appliances are stated as not impacted in the provided advisory data.

Likely exposure

Exposure is highest where the User-ID Authentication Portal is enabled and reachable from untrusted networks. Risk is reduced when portal access is restricted to trusted internal IP addresses. Affected environments include PAN-OS on PA-Series and VM-Series firewalls in the listed 10.2, 11.1, 11.2, and 12.1 version sets.

Exploitation context

CISA KEV inclusion supports active exploitation. The vulnerability requires no authentication, no user interaction, and network reachability to the vulnerable portal service. Root-level execution on a firewall creates high risk for perimeter compromise, traffic interception, persistence, and downstream network access.

Researcher notes

The source bundle does not name fixed PAN-OS versions. Do not assume a patch level without the live vendor advisory. CISA KEV supports active exploitation, but the bundle does not provide exploit details. Siemens has a referenced advisory; product-specific impact is not described in the provided data.

Mitigation direction

  • Review Palo Alto Networks advisory for fixed PAN-OS releases and upgrade guidance.
  • Restrict User-ID Authentication Portal access to trusted internal IP addresses only.
  • Remove internet exposure to the portal wherever operationally possible.
  • Prioritize affected PA-Series and VM-Series firewalls over unaffected products.
  • Consult Siemens advisory if your environment depends on referenced Siemens guidance.

Validation and detection

  • Inventory PAN-OS firewalls and record exact PAN-OS versions.
  • Confirm whether User-ID Authentication Portal or Captive Portal is enabled.
  • Verify portal reachability from internet and untrusted network segments.
  • Check access controls restrict the portal to trusted internal IP addresses.
  • Confirm Prisma Access, Cloud NGFW, and Panorama are not misclassified as affected.
Prepared
Confidence
high
Sources
5

Public sources used

Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.

Potential ATT&CK relevance

Conservative CVE-to-ATT&CK context

These mappings and lookup hints may be relevant to the vulnerability behavior, CWE, affected product, or exposure path. Glexia-inferred context is not an official MITRE, ATT&CK, CWE, or CVE Program mapping.

ATT&CK lookup starting points

Use these exact CWE pages and searches to review the Glexia ATT&CK library from this CVE's weakness and description context.

cwe · low confidence lookup

CWE-787: Exact CWE lookup

Use the exact CWE identifier as the starting point before reviewing related ATT&CK behavior. Open the exact CWE lookup page first, then review the ATT&CK searches from that MITRE weakness context. This is a Glexia lookup hint, not an official ATT&CK mapping.

Open ATT&CK lookup
description · low confidence lookup

Execution behavior lookup

The CVE wording references code or command execution, so execution technique review may help defensive triage. This is a Glexia inferred lookup path, not an official MITRE, ATT&CK, or CVE Program mapping.

Open ATT&CK lookup
cve · low confidence lookup

CVE-2026-0300 mapping review

Open the CVE-to-ATT&CK bridge for reviewed, inferred, or future official mappings tied to this CVE.

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Vulnerability profileCVE Program record
Severity
Critical
CVSS
9.3 (4.0)
Known Exploited
Yes
Published

Vector: 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

Official CVE source material

CNA and ADP enrichment extracted from CVE v5

These fields come from the CVE record and ADP containers, not from Glexia's Take. They preserve time-varying source decisions such as CISA SSVC, KEV status, CVSS metrics, and provider references.

2CVSS vectors
7Timeline events
2ADP providers
4Source links

CISA KEV status

Status
Known exploited
Source
CISA-ADP
Date added
KEV reference

SSVC decision data

CISA-ADPCISA Coordinator
Timestamp
Version
2.0.3
Exploitation: activeAutomatable: yesTechnical Impact: total

CVSS vector scores

2 official scores

We collect every scored CVSS vector available in the official CNA and ADP containers. When more than one version is present, the table keeps the source vectors side by side instead of collapsing them into the highest score.

ScoreVersionSeverityVectorExploitImpactSource
9.3CVSS 4.0CriticalCVSS: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——palo_alto
8.7CVSS 4.0HighCVSS: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——palo_alto

Vulnerability scoring details

Base CVSS 4.0 score

9.3Critical
CVSS 4.0 vector shape for CVE-2026-0300Attack VectorAttack ComplexityAttack RequirementsPrivileges RequiredUser InteractionVS ConfidentialityVS IntegrityVS AvailabilitySS ConfidentialitySS IntegritySS Availability

Vector: 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
NetworkAdjacentLocalPhysical
Attack Complexity
LowHigh
Attack Requirements
NonePresent
Privileges Required
NoneLowHigh
User Interaction
NonePassiveActive
VS Confidentiality
HighLowNone
VS Integrity
HighLowNone
VS Availability
HighLowNone
SS Confidentiality
HighLowNone
SS Integrity
HighLowNone
SS Availability
HighLowNone

Vulnerability timeline

Timeline events are normalized from CVE metadata, CNA source timelines, ADP timelines, and KEV metadata when present.

  1. CVE reservedCVE Program

    The CVE ID was reserved by the assigning CNA.

  2. Source timelinepalo_alto

    Initial publication.

  3. Added to KEVCISA-ADP

    CISA Known Exploited Vulnerabilities metadata lists this CVE as known exploited.

  4. ADP timelineCISA-ADP

    CVE-2026-0300 added to CISA KEV

  5. Source timelinepalo_alto

    Updated with Threat Prevention ID and clarified the Required Configuration section.

  6. CVE publishedCVE Program

    The CVE record was published.

  7. CVE updatedCVE Program

    The CVE record metadata indicates this as the latest update time.

ADP provider summaries

CISA-ADPCISA ADP Vulnrichment
other:ssvcother:kev
  • 2026-05-06T00:00:00.000Z: CVE-2026-0300 added to CISA KEV
siemens-SADPADP container

Source materials

Affected products

Products and packages named in the record

VendorProductVersion / packageStatus
Palo Alto NetworksCloud NGFWAllunaffected
Palo Alto NetworksPAN-OS12.1.0, 11.2.0, 11.1.0, 10.2.0unaffected
Palo Alto NetworksPrisma AccessAllunaffected
Weakness

CWE details

CWE-787

CWE links open Glexia weakness intelligence pages with official CWE context, developer remediation guidance, and related CVE mappings.