CVE-2026-0300: Palo Alto Networks PAN-OS Critical Vulnerability

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.

Technical Analysis

Weakness Classification

This vulnerability is classified as CWE-787, Out-of-bounds Write. The software writes data past the end or before the beginning of a buffer, potentially enabling arbitrary code execution or crashes.

Attack Vector Breakdown

• Attack Vector: Network
• Attack Complexity: Low
• Privileges Required: None
• User Interaction: None
• Scope: Unchanged
• Confidentiality: High
• Integrity: High
• Availability: High

Impact Analysis

This vulnerability is exploitable over the network, meaning any system reachable via the internet or internal network is potentially at risk without physical access. The attack complexity is low, requires no special privileges, and needs no user interaction, making it straightforward to exploit at scale. Successful exploitation can result in full confidentiality breach (complete data disclosure), complete integrity compromise (data modification or code execution), total availability loss (denial of service). The software writes data past the end or before the beginning of a buffer, potentially enabling arbitrary code execution or crashes.

Exploitation Probability (EPSS): 32.1% chance of exploitation in the next 30 days (98th percentile). This is a significantly elevated exploitation probability, prioritize patching.

Exploit Availability

Public exploit code or proof-of-concept is available for CVE-2026-0300. This significantly increases the risk of exploitation, as attackers can use or adapt existing exploit code rather than developing their own. A public exploit reference has been identified. Organizations should treat this as an urgent patching priority.

Is CVE-2026-0300 being exploited?

Yes. CVE-2026-0300 is listed in CISA's Known Exploited Vulnerabilities (KEV) catalog, restricted to CVEs with confirmed active exploitation in the wild. CISA added this vulnerability on 2026-05-06. Inclusion in KEV triggers the patching mandate under BOD 22-01 for U.S. federal civilian agencies, with a remediation deadline of 2026-05-09. Additionally, public exploit code is available, which lowers the barrier for attackers.

How to fix CVE-2026-0300

Upgrade PAN-OS to the fixed version listed in the Palo Alto Networks Security Advisory. Use the PAN-OS software update process through the management interface or CLI. If immediate upgrade is not possible, apply Threat Prevention signatures and restrict management interface access as described in the advisory. Check the Palo Alto Networks Security Advisories page for the specific patch or update. CISA's Known Exploited Vulnerabilities catalog requires U.S. federal agencies to remediate this vulnerability by the due date shown below under Binding Operational Directive 22-01. Private organizations should treat KEV entries as priority-one patches because active exploitation has been confirmed in the wild.

Related Vulnerabilities

Other actively exploited vulnerabilities affecting PAN-OS or sharing the same weakness (CWE-787):

• CVE-2026-0257 (Critical 9.1) [same product], Authentication bypass vulnerabilities in the GlobalProtect portal and gateway…

Frequently asked questions

Is CVE-2026-0300 critical?

CVE-2026-0300 has a CVSS 3.1 base score of 9.8, Critical severity. It should be treated as a priority patch, especially given the active exploitation confirmed by CISA. The availability of public exploit code further increases the urgency.

Is CVE-2026-0300 being actively exploited?

Yes, CISA added CVE-2026-0300 to the Known Exploited Vulnerabilities catalog on 2026-05-06. Inclusion in KEV means CISA has confirmed in-the-wild exploitation. Public exploit code has also been identified, making exploitation accessible to a broader range of threat actors.

How do I patch CVE-2026-0300?

Apply the security update from Palo Alto Networks for PAN-OS. Federal agencies must remediate by 2026-05-09 under BOD 22-01. Refer to the Palo Alto Networks Security Advisories for the official patch.

What type of vulnerability is CVE-2026-0300?

CVE-2026-0300 is classified under CWE-787 (Out-of-bounds Write). The software writes data past the end or before the beginning of a buffer, potentially enabling arbitrary code execution or crashes.

What is the CVSS score for CVE-2026-0300?

CVE-2026-0300 has a CVSS 3.1 base score of 9.8, classifying it as Critical severity. The attack vector is Network, attack complexity is Low, and no privileges are required.