CVE-2026-0300

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

CVSS 4.0 Critical 9.3Known exploited (CISA KEV)

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

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.

Key data

CVSS 4.0 Critical 9.3

Score published by palo_alto in the CVE record.

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
The vulnerable component can be reached over a network, possibly from the Internet.
Attack complexity: Low
No measurable action is needed to get around the system's built-in security controls. The attack is repeatable.
Attack requirements: None
The attack works without any special deployment or execution conditions.
Privileges required: None
No account or privileges are needed.
User interaction: None
No action from any user is needed.
Vulnerable system: confidentiality: High
Serious or total effect on the secrecy of data.
Vulnerable system: integrity: High
Serious or total effect on the trustworthiness of data.
Vulnerable system: availability: High
Serious or total effect on availability.
Subsequent systems: confidentiality: Low
Limited effect on other systems' data secrecy.
Subsequent systems: integrity: Low
Limited effect on other systems' data trustworthiness.
Subsequent systems: availability: None
No effect on other systems' availability.

Metric	Value	What it means
Attack vector	Network	The vulnerable component can be reached over a network, possibly from the Internet.
Attack complexity	Low	No measurable action is needed to get around the system's built-in security controls. The attack is repeatable.
Attack requirements	None	The attack works without any special deployment or execution conditions.
Privileges required	None	No account or privileges are needed.
User interaction	None	No action from any user is needed.
Vulnerable system: confidentiality	High	Serious or total effect on the secrecy of data.
Vulnerable system: integrity	High	Serious or total effect on the trustworthiness of data.
Vulnerable system: availability	High	Serious or total effect on availability.
Subsequent systems: confidentiality	Low	Limited effect on other systems' data secrecy.
Subsequent systems: integrity	Low	Limited effect on other systems' data trustworthiness.
Subsequent systems: availability	None	No effect on other systems' availability.

CVSS 4.0 High 8.7

Score published by palo_alto in the CVE record.

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
The attacker needs to be on the same shared network segment or a closely related one.
Attack complexity: Low
No measurable action is needed to get around the system's built-in security controls. The attack is repeatable.
Attack requirements: None
The attack works without any special deployment or execution conditions.
Privileges required: None
No account or privileges are needed.
User interaction: None
No action from any user is needed.
Vulnerable system: confidentiality: High
Serious or total effect on the secrecy of data.
Vulnerable system: integrity: High
Serious or total effect on the trustworthiness of data.
Vulnerable system: availability: High
Serious or total effect on availability.
Subsequent systems: confidentiality: Low
Limited effect on other systems' data secrecy.
Subsequent systems: integrity: Low
Limited effect on other systems' data trustworthiness.
Subsequent systems: availability: None
No effect on other systems' availability.

Metric	Value	What it means
Attack vector	Adjacent	The attacker needs to be on the same shared network segment or a closely related one.
Attack complexity	Low	No measurable action is needed to get around the system's built-in security controls. The attack is repeatable.
Attack requirements	None	The attack works without any special deployment or execution conditions.
Privileges required	None	No account or privileges are needed.
User interaction	None	No action from any user is needed.
Vulnerable system: confidentiality	High	Serious or total effect on the secrecy of data.
Vulnerable system: integrity	High	Serious or total effect on the trustworthiness of data.
Vulnerable system: availability	High	Serious or total effect on availability.
Subsequent systems: confidentiality	Low	Limited effect on other systems' data secrecy.
Subsequent systems: integrity	Low	Limited effect on other systems' data trustworthiness.
Subsequent systems: availability	None	No effect on other systems' availability.

CVSS is owned and managed by FIRST.Org, Inc. (FIRST) and is used by permission. Each CVSS score on this site is shown together with its vector string, as published in the CVE record by the source named next to it. Learn more at first.org/cvss.

EPSS

Exploit Prediction Scoring System by FIRST: an estimate of the probability that exploitation activity will be observed in the next 30 days.

Score: 0.41714 (41.7% probability)
Percentile: 98.7%
Scores of: Nov 10, 2026
Model: v2026.06.15

CISA Known Exploited Vulnerabilities

This CVE is listed in the CISA KEV catalog.

Name in the catalog: Palo Alto Networks PAN-OS Out-of-bounds Write Vulnerability
Added to the catalog: May 6, 2026
Federal due date: May 9, 2026

CISA assessment as of May 6, 2026

Stakeholder-Specific Vulnerability Categorization (SSVC) decision points added by CISA.

Exploitation: Recorded by CISA as active
Automatable: yes
Technical impact: total

Weakness (CWE)

CWE catalog version 5.0.

CWE-787Out-of-bounds Write

Affected products

Products listed in the CVE record, as the CNA published them.

Palo Alto Networks PAN-OS
- affected: 12.1.0 up to before 12.1.7
- affected: 11.2.0 up to before 11.2.12
- affected: 11.1.0 up to before 11.1.15
- affected: 10.2.0 up to before 10.2.18-h6

Listed as not affected

Palo Alto Networks Cloud NGFW
Palo Alto Networks Prisma Access

References

Links listed in the CVE record. They lead to other sites, which CubePath does not control.

security.paloaltonetworks.com/CVE-2026-0300vendor-advisory

Timeline

ID reservedNov 3, 2025
Added to CISA KEVMay 6, 2026
Record publishedMay 6, 2026
Record last updatedOct 15, 2026

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About CubePath

CubePath is a cloud provider with data centers in Europe and the United States. It offers VPS, bare metal servers and DDoS protection.

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Data from the CVE Program (MITRE), CISA KEV and FIRST EPSS. CVSS is owned by FIRST and used by permission. Not affiliated with or endorsed by MITRE, CISA or FIRST. Data as of Nov 10, 2026, 19:10 UTC. Sources and licenses