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CVE-2026-0300: Palo Alto Networks PAN-OS Out-of-bounds Write Vulnerability

In short

Palo Alto Networks PAN-OS has a weakness classified as out-of-bounds write (CWE-787). CISA added it to its Known Exploited Vulnerabilities catalog on 2026-05-06. NVD lists CVSS 4.0 at 9.3 CRITICAL.

What it is

“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.” — CISA KEV, retrieved 2026-11-01
“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.” — NVD, retrieved 2026-11-01

Who is affected

Palo Alto Networks PAN-OS. NVD lists the following versions as affected:

  • Paloaltonetworks PAN-OS: version 10.2.0
  • Paloaltonetworks PAN-OS: version 10.2.1
  • Paloaltonetworks PAN-OS: version 10.2.2
  • Paloaltonetworks PAN-OS: version 10.2.3
  • Paloaltonetworks PAN-OS: version 10.2.4
  • Paloaltonetworks PAN-OS: version 10.2.5
  • Paloaltonetworks PAN-OS: version 10.2.6
  • Paloaltonetworks PAN-OS: version 10.2.7
  • Paloaltonetworks PAN-OS: version 10.2.8
  • Paloaltonetworks PAN-OS: version 10.2.9
  • Paloaltonetworks PAN-OS: version 10.2.10
  • Paloaltonetworks PAN-OS: version 10.2.11
  • Paloaltonetworks PAN-OS: version 10.2.12
  • Paloaltonetworks PAN-OS: version 10.2.13
  • Paloaltonetworks PAN-OS: version 10.2.14
  • Paloaltonetworks PAN-OS: version 10.2.15
  • Paloaltonetworks PAN-OS: version 10.2.16
  • Paloaltonetworks PAN-OS: version 10.2.17
  • Paloaltonetworks PAN-OS: version 10.2.18
  • Paloaltonetworks PAN-OS: version 11.1.0
  • Paloaltonetworks PAN-OS: version 11.1.1
  • Paloaltonetworks PAN-OS: version 11.1.2
  • Paloaltonetworks PAN-OS: version 11.1.3
  • Paloaltonetworks PAN-OS: version 11.1.4
  • Paloaltonetworks PAN-OS: version 11.1.5
  • Paloaltonetworks PAN-OS: version 11.1.6
  • Paloaltonetworks PAN-OS: version 11.1.7
  • Paloaltonetworks PAN-OS: version 11.1.8
  • Paloaltonetworks PAN-OS: version 11.1.9
  • Paloaltonetworks PAN-OS: version 11.1.10
  • Paloaltonetworks PAN-OS: version 11.1.11
  • Paloaltonetworks PAN-OS: version 11.1.12
  • Paloaltonetworks PAN-OS: version 11.1.13
  • Paloaltonetworks PAN-OS: version 11.1.14
  • Paloaltonetworks PAN-OS: version 11.2.0
  • Paloaltonetworks PAN-OS: version 11.2.1
  • Paloaltonetworks PAN-OS: version 11.2.2
  • Paloaltonetworks PAN-OS: version 11.2.3
  • Paloaltonetworks PAN-OS: version 11.2.4
  • Paloaltonetworks PAN-OS: version 11.2.5
  • Paloaltonetworks PAN-OS: version 11.2.6
  • Paloaltonetworks PAN-OS: version 11.2.7
  • Paloaltonetworks PAN-OS: version 11.2.8
  • Paloaltonetworks PAN-OS: version 11.2.9
  • Paloaltonetworks PAN-OS: version 11.2.10
  • Paloaltonetworks PAN-OS: version 11.2.11
  • Paloaltonetworks PAN-OS: version 12.1.2
  • Paloaltonetworks PAN-OS: version 12.1.3
  • Paloaltonetworks PAN-OS: version 12.1.4
  • Paloaltonetworks PAN-OS: version 12.1.5
  • Paloaltonetworks PAN-OS: version 12.1.6
  • Siemens Ruggedcom ape1808 Firmware: all versions listed (no range given)

Exploitation status

CISA KEV added: 2026-05-06. Known ransomware campaign use: Not reported by CISA. Due date CISA set for US federal civilian agencies: 2026-05-09.

Scores

NVD CVSS 4.0: 9.3 CRITICAL; 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/E:A/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:Y/R:U/V:C/RE:M/U:Red; source [email protected].

EPSS by FIRST: 41.71%; percentile 98.69; score date 2026-10-31. EPSS estimates the probability of exploitation in the next 30 days.

CWE: CWE-787.

Timeline

Source events
DateEvent
2026-05-06CISA KEV added
2026-05-06T19:16:35.730NVD published
2026-05-09CISA KEV due
2026-10-26T19:10:00.163NVD last modified
2026-10-31FIRST EPSS score

CISA 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.” — CISA KEV

What to do

  • Confirm whether you run Palo Alto Networks PAN-OS and which version.
  • Apply the vendor update or mitigation in the advisory.
  • Follow CISA’s required action.
  • Review the vendor guidance on signs of compromise.
  • Track the fix through completion.

References

Sources and dates

CISA Known Exploited Vulnerabilities Catalog, version 2026.10.30; retrieved 2026-11-01. CISA KEV data: CC0 1.0. No endorsement by CISA.

NVD retrieved: 2026-11-01. This product uses the NVD API but is not endorsed or certified by the NVD.

EPSS scores by FIRST; score date 2026-10-31.

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