Vulnerability

CVE-2026-0300

Critical· 9.8KEVCVSS9.8EPSS6%

.rules3/5

Palo Alto Networks PAN-OS Out-of-bounds Write Vulnerability

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.

Threat signal

100/100

Severe

Severity

critical

CVSS

9.8

EPSS

Active

KEV

CISA KEV — actively exploited

35d overdue

AffectedPalo Alto Networks — PAN-OS

Added to KEV

2026-05-06

Federal patch due (BOD 22-01)

2026-05-09

Required action (CISA verbatim)

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.

Vendor advisory + references

CISA description: “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.”

CVSS

v3.1Open in FIRST calculator →

9.8/ 10CRITICALCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Attack VectorNetworkExploitable remotely over the internet — no local access needed.
Attack ComplexityLowNo special conditions — exploit works reliably.
Privileges RequiredNoneUnauthenticated — no credentials needed.
User InteractionNoneFully automated — no victim action needed.
ScopeUnchangedImpact contained to the vulnerable component.
Confidentiality ImpactHighTotal disclosure of sensitive data.
Integrity ImpactHighTotal compromise of integrity — full data modification possible.
Availability ImpactHighTotal loss of availability — full DoS possible.

EPSS

Exploit prediction · 30-day horizonFIRST.org →

6.13%

probability of exploitation in next 30 days

p91

higher than 91% of all CVEs

3-day trend↑ 1.2pp

Mid-pack — moderate exploitation likelihood.

Vendor VEX

No VEX statements published for CVE-2026-0300. Vendors publish VEX (Vulnerability Exploitability eXchange) to assert per-product whether a CVE is actually exploitable in their distribution.

SSVCAct

Active exploitation with total impact on essential/support systems

exploitation: active
automatable: yes
impact: total
mission: support

Lifecycle

2026-05-06Added to CISA KEVransomware: Unknown
2026-05-06Published
2026-05-09Federal patch due (BOD 22-01)
2026-06-12Last modified1 source

Mentions in news & research

No source-event history recorded yet. New revisions will appear here as ingestors re-fetch this CVE.