What is CVE-2026-0300?
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.
The record classifies CVE-2026-0300 under weakness class CWE-787. Its CVSS v3 base vector states that the flaw is reachable remotely over the network, needs no prior authentication, needs no user interaction, and has high impact on confidentiality, integrity, availability. 10 affected-product entries are recorded, across 1 vendor, listed below. The identifier was first published 152 days ago.
Severity and exploitation probability
- CVSS v3.1 base score
- 9.8 — CRITICAL
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H - CVSS v4.0 base score
- 9.3
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 - EPSS (FIRST)
- 4.5% probability of exploitation in the next 30 days, higher than 89.3% of all scored CVEs
- CISA KEV
- Listed since 2026-05-06, federal remediation deadline 2026-05-09 — used in known ransomware campaigns
- Threadlinqs priority
- 10/10 — CISA lists it as used in ransomware, which Threadlinqs scores at the maximum
- Published
- 2026-05-06, last modified 2026-05-12
Is CVE-2026-0300 being exploited?
CISA added CVE-2026-0300 to the Known Exploited Vulnerabilities catalog on 2026-05-06, which means the agency holds evidence of exploitation in the wild; US federal civilian agencies had to remediate it by 2026-05-09 under BOD 22-01. CISA flags the vulnerability as one used in known ransomware campaigns. It currently carries a trending score of 37 in the Threadlinqs vulnerability feed.
Affected products and versions
- Paloaltonetworks: Pan-Os, Pa-1410, Pa-1420, Pa-3410, Pa-3420, Pa-3430, Pa-3440, Pa-410, Pa-410R, Pa-410R-5G
How to fix CVE-2026-0300
Vendor advisory: https://security.paloaltonetworks.com/CVE-2026-0300. Because CVE-2026-0300 is KEV-listed, US federal civilian agencies were required to apply the vendor fix, or stop using the product, by 2026-05-09. Apply the vendor fix referenced above to every affected product listed in this record, then confirm the running version against the vendor advisory.
Threat activity tracking CVE-2026-0300
1 tracked threat in the Threadlinqs corpus references CVE-2026-0300, either in the campaign’s CVE list or as an indicator on the campaign record.
Sources
Seeded from cveorg and not yet processed by the Threadlinqs enrichment pipeline, so blank CVSS, EPSS or KEV fields above mean NOT MEASURED rather than measured-absent.