CVE 2026-0300 is a critical vulnerability with CVSS score of 9.3

PaloAlto Networks has issued strict advisory for its customers after an actively exploited zero-day vulnerability, affected its firewall operating system, PAN-OS. CVE 2026-0300 allows attackers to gain full control of affected systems without authentication.

The zero-day bug stems from a buffer overflow weakness, allowing unauthenticated attackers to execute arbitrary code with root privileges on Internet-exposed PA-Series and VM-Series firewalls via specially crafted packets.

Active Exploitation Observed in the Wild

Palo Alto Networks confirmed that exploitation attempts have already been observed in its advisory and urged its customers and organizations to mitigate exposure immediately.

What did the vulnerability affect:

• PAN-OS 10.2 below 10.2.7-h34, 10.2.10-h36, 10.2.13-h21, 10.2.16-h7, 10.2.18-h6
• PAN-OS 11.1 below 11.1.4-h33, 11.1.6-h32, 11.1.7-h6, 11.1.10-h25, 11.1.13-h5, 11.1.15
• PAN-OS 11.2 below 11.2.4-h17, 11.2.7-h13, 11.2.10-h6, 11.2.12
• PAN-OS 12.1 below 12.1.4-h5, 12.1.7

Excluded from vulnerability are Prisma Access, Cloud Next-Generation Firewall (Cloud NGFW), and Panorama appliances are not impacted by this vulnerability.

PoC of CVE 2026-0300

PaloAlto published a PoC on May 6, showing how an unauthenticated request to the User-ID Authentication Portal can reliably trigger the buffer overflow and achieve root-level RCE on affected PAN-OS versions.

While the repository is framed as research code and includes legal disclaimers, it materially lowers the barrier to exploitation by validating exploit mechanics.

Palo Alto Networks has not shared details about who is behind the attacks and has not released indicators of compromise at the time of writing.

Patching & Remediation

Since security patches takes time, PaloAlto recommends reducing exposure is the most effective way to contain risk. Palo Alto Networks proactively alerted customers to the zero-day, a step that allowed defenders to take action on potentially exposed instances. 

If the User-ID Authentication Portal is not required for business operations, Palo Alto Networks recommends disabling it entirely. Firewalls that do not have the Authentication Portal enabled are not affected by this vulnerability.

The company has stated that security fixes will be released in stages between May 13-28, depending on the PAN‑OS version in use.

In advance of these patches, Palo Alto released a Threat Prevention signature on May 5 for PAN-OS 11.1 and newer to help detect or block exploitation attempts. Applying this signature, where supported, provides interim protection but does not replace the need to reduce exposure and deploy patches once available.

For security teams, immediate focus should be on identifying PA-Series and VM-Series firewalls with the User-ID Authentication Portal enabled, confirming whether those services are reachable from untrusted networks, and scheduling timely deployment of Palo Alto’s fixes as they are released.

Monitoring unexpected firewall behavior or unplanned configuration changes provides additional awareness during the period of active exploitation.

A similar authentication bypass vulnerability (CVE-2025-0108) was discovered in Palo Alto Networks PAN-OS allows unauthenticated attackers with network access to bypass authentication on the management web interface on 20 feb 2025. https://intruceptlabs.com/2025/02/palo-alto-firewall-vulnerabilities-under-active-exploitation/

Firewall infrastructure attack increased in recent years so are the Stakes for Enterprise and Critical Infrastructure

Firewalls are the prime targets because if firewall can be controlled the entire network is in hands of hackers. In recent years, the frequency and success of exploits targeting firewall vulnerabilities have been alarmingly high. Threat actors take on management interfaces, login pages and authentication portals as most common targets for both opportunistic and targeted campaigns.

A successful compromise in the firewall can allow attackers to:

• Intercept entire network traffic
• Disable security protections
• Move laterally inside corporate networks
• Establish persistent backdoors

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Sources: https://fieldeffect.com/blog/palo-alto-firewall-zero-day-unauthenticated-root-access#:~:text=On%20May%205%2C%202026%2C%20Palo,systems%20accessible%20from%20untrusted%20networks.

Sources: https://www.bleepingcomputer.com/news/security/palo-alto-networks-warns-of-actively-exploited-firewall-zero-day