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CVE-2026-0300

critical

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.

References

https://cert-portal.siemens.com/productcert/html/ssa-967325.html

https://security.paloaltonetworks.com/CVE-2026-0300

https://www.securityweek.com/palo-alto-zero-day-exploited-in-campaign-bearing-hallmarks-of-chinese-state-hacking/

https://www.bleepingcomputer.com/news/security/pan-os-firewall-rce-zero-day-exploited-in-attacks-since-april-9/

https://unit42.paloaltonetworks.com/captive-portal-zero-day/

https://thehackernews.com/2026/05/pan-os-rce-exploit-under-active-use.html

https://securityaffairs.com/191831/security/nation-state-actors-exploit-palo-alto-pan-os-zero-day-for-weeks.html

https://securityaffairs.com/191780/security/u-s-cisa-adds-a-flaw-in-palo-alto-networks-pan-os-to-its-known-exploited-vulnerabilities-catalog.html

https://www.securityweek.com/palo-alto-networks-to-patch-zero-day-exploited-to-hack-firewalls/

https://www.databreachtoday.com/palo-alto-firewalls-being-exploited-no-patch-yet-available-a-31612

https://www.cisa.gov/news-events/alerts/2026/05/06/cisa-adds-one-known-exploited-vulnerability-catalog

https://www.bleepingcomputer.com/news/security/palo-alto-networks-warns-of-actively-exploited-firewall-zero-day/

https://therecord.media/palo-alto-warns-of-critical-software-bug-firewalls

https://thehackernews.com/2026/05/palo-alto-pan-os-flaw-under-active.html

https://securityaffairs.com/191748/security/palo-alto-networks-pan-os-flaw-exploited-for-remote-code-execution.html

https://cyberscoop.com/palo-alto-networks-pan-os-firewall-zero-day-vulnerability-exploited/

https://www.cisa.gov/news-events/ics-advisories/icsa-26-139-02

https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2026-0300

Details

Source: Mitre, NVD

Published: 2026-05-06

Updated: 2026-05-12

Known Exploited Vulnerability (KEV)

Risk Information

CVSS v2

Base Score: 10

Vector: CVSS2#AV:N/AC:L/Au:N/C:C/I:C/A:C

Severity: Critical

CVSS v3

Base Score: 9.8

Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Severity: Critical

CVSS v4

Base Score: 9.3

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

Severity: Critical

EPSS

EPSS: 0.0465

Vulnerability Watch

Tenable Research has classified this CVE under the following Vulnerability Watch classification, which includes active and historical (inactive) classifications. You can learn more about these classifications on our blog.

Vulnerability of Interest