CVE-2026-0300
CRITICALCVE-2026-0300 is a critical-severity (CVSS 9.8) Out-of-bounds Write vulnerability in paloaltonetworks pan-os. It is in CISA's Known Exploited Vulnerabilities catalog (added 2026-05-06) — treat it as actively exploited and patch now. O3 Security detects and blocks CVE-2026-0300 exploitation at runtime via eBPF exploit-chain detection and L7 egress monitoring, even on unpatched systems.
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…
Exploitation Status
Actively exploited in the wild
- Confirmed by CISA's Known Exploited Vulnerabilities catalog on 2026-05-06. Federal agencies were required to remediate by 2026-05-09.
- CISA assesses this as automatable — exploitation doesn’t require manual, per-target effort, which raises the odds of mass scanning and opportunistic attacks.
- A successful exploit gives an attacker total control of the affected component, not partial access.
Exploitation and automatability from CISA (KEV catalog and SSVC triage) for CVE-2026-0300.
EPSS Exploitation Probability
EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.
How urgent is this, really
CVE-2026-0300 plotted by exploitation likelihood (EPSS) against impact (CVSS). The shaded corner — EPSS 50%+ and CVSS 7.0+ — is where this CVE doesn't sit, though severity or exploitability alone can still warrant action.
Where this sits among everything scored
Of 369,023 CVEs with a current EPSS score, this one falls in the 10–50% band (highlighted). Real counts from FIRST.org, not a sample — log-scaled since the landscape is heavily right-skewed.
Description
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.
Affected Products
pan-ospaloaltonetworksruggedcom ape1808 firmwaresiemensResearch use only. For defensive security, authorized penetration testing, and academic research only. Never execute exploit code against systems without explicit written authorization.
p3Nt3st3r-sTAr/CVE-2026-0300-POC
qassam-315/PAN-OS-User-ID-Buffer-Overflow-PoC
A research-grade Proof-of-Concept (PoC) for CVE-2026-0300, targeting the
matad0r-maghribi/CVE-2026-0300-PANOS
Security Research and Proof-of-Concept (PoC) for CVE-2026-0300 : Unauthe
Detection & mitigation playbook
Vendor / applianceDetect
Inventory every paloaltonetworks pan-os deployment and check each version against the affected-products list above. Because the exploit targets the running system rather than your application code, also watch for remote code execution at the network and runtime layer — O3 flags the exploit behaviour from runtime telemetry and egress traffic even before a vulnerable build is confirmed.
Remediation status
No patch has shipped for CVE-2026-0300 yet — track the paloaltonetworks pan-os advisory for a fixed release and apply the workarounds below in the meantime.
Mitigate without a patch
Cut exposure now: restrict the management/admin interface to trusted networks, segment the device, and apply the vendor's recommended configuration mitigations and any WAF/IPS signature. O3's runtime protection blocks the exploit chain at execution, holding the line on unpatched or end-of-life systems until you can patch.
How O3 protects you
O3 detects and blocks CVE-2026-0300 exploitation at runtime: eBPF exploit-chain detection, plus L7 egress monitoring that catches the post-exploitation callback and severs the attacker's outbound channel.
Tailored to CVE-2026-0300. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is CVE-2026-0300 being exploited in your environment?
O3's eBPF runtime sensors and L7 egress monitoring detect and block the CVE-2026-0300 exploit chain at execution — protecting unpatched and end-of-life systems until the vendor patch is applied.