Palo Alto Networks PAN-OS Out-of-bounds Write Vulnerability
Palo Alto Networks / PAN-OS
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.
- CVE identifier
- CVE-2026-0300
- Added to KEV
- May 6, 2026
- CISA catalog dueDate
- May 9, 2026
The dates above are catalog fields. The addition date does not establish when the vulnerability was discovered or first exploited. Confirm which requirements apply to your organisation separately.
Publisher's required action
Apply mitigations per vendor instructions, follow applicable BOD 22-01 guidance for cloud services, or discontinue use of the product if mitigations are unavailable. Until the vendor releases an official fix, the following workaround should be implemented: - Restrict User-ID Authentication Portal access to only trusted zones. - Disable User-ID Authentication Portal if not required. 5/13/2026: Palo Alto has released a variety of patches. If these are relevant to your environment, please apply the designated patch.
This wording is attributed to the CISA snapshot. Verify current vendor guidance, affected versions and your deployment before applying changes.
Keep the signals separate.
- Ransomware use, as reported by CISA
- Unknown
- CVSS severity
- Not supplied by KEV
- EPSS probability
- 31.72%
EPSS score date: 2026-09-27T12:00:21Z. Percentile: 98.24%. Model version: v2026.06.15.
A dated estimate of exploitation probability over the following 30 days, not a severity score or a probability of a breach in your environment.
Inspect the EPSS source ↗“Unknown” ransomware use is an unknown source field, not proof that ransomware activity has not occurred.
Source notes
https://security.paloaltonetworks.com/CVE-2026-0300 ; https://nvd.nist.gov/vuln/detail/CVE-2026-0300
Source & freshness
Source updated: Sep 27, 2026, 9:30 PM UTC
Successfully checked: Sep 27, 2026, 11:50 PM UTC
This snapshot is older than 36 hours. Check current publisher guidance.
Automated source record, not an editorial advisory or an independent discovery. No affected or fixed version is inferred, and no organisation-specific risk rating is generated.