CVE-2026-0300
CRITICAL CISA KEVDescription
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.
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CVSS v3.1 Score
9.8
CRITICAL
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
EPSS — Exploit Prediction
0.0454
Probability of exploitation
0.89%
Percentile rank
EPSS estimates the probability that this vulnerability will be exploited in the wild within the next 30 days. A higher score means more likely to be exploited.
CISA Known Exploited Vulnerability
This vulnerability is actively exploited in the wild.
Added: May 6, 2026
Remediation due: May 9, 2026
Weakness Type (CWE)
CWE-787
Out-of-bounds Write
Affected Products
| Vendor | Product |
|---|---|
| paloaltonetworks | pan-os |
| paloaltonetworks | pan-os |
| paloaltonetworks | pan-os |
| paloaltonetworks | pan-os |
| paloaltonetworks | pan-os |
| paloaltonetworks | pan-os |
| paloaltonetworks | pan-os |
| paloaltonetworks | pan-os |
| paloaltonetworks | pan-os |
| paloaltonetworks | pan-os |
| paloaltonetworks | pan-os |
| paloaltonetworks | pan-os |
| paloaltonetworks | pan-os |
| paloaltonetworks | pan-os |
| paloaltonetworks | pan-os |
| paloaltonetworks | pan-os |
| paloaltonetworks | pan-os |
| paloaltonetworks | pan-os |
| paloaltonetworks | pan-os |
| paloaltonetworks | pan-os |
| paloaltonetworks | pan-os |
| paloaltonetworks | pan-os |
| paloaltonetworks | pan-os |
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| paloaltonetworks | pan-os |
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| paloaltonetworks | pan-os |
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| paloaltonetworks | pan-os |
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| paloaltonetworks | pan-os |
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| paloaltonetworks | pan-os |
| paloaltonetworks | pan-os |
| paloaltonetworks | pan-os |
| paloaltonetworks | pan-os |
| paloaltonetworks | pan-os |
| paloaltonetworks | pan-os |
| paloaltonetworks | pan-os |
| paloaltonetworks | pan-os |
| paloaltonetworks | pan-os |
| paloaltonetworks | pan-os |
| paloaltonetworks | pa-1410 |
| paloaltonetworks | pa-1420 |
| paloaltonetworks | pa-3410 |
| paloaltonetworks | pa-3420 |
| paloaltonetworks | pa-3430 |
| paloaltonetworks | pa-3440 |
| paloaltonetworks | pa-410 |
| paloaltonetworks | pa-410r |
| paloaltonetworks | pa-410r-5g |
| paloaltonetworks | pa-415 |
| paloaltonetworks | pa-415-5g |
| paloaltonetworks | pa-440 |
| paloaltonetworks | pa-445 |
| paloaltonetworks | pa-450 |
| paloaltonetworks | pa-450r |
| paloaltonetworks | pa-450r-5g |
| paloaltonetworks | pa-455 |
| paloaltonetworks | pa-455-5g |
| paloaltonetworks | pa-455r-5g |
| paloaltonetworks | pa-460 |
| paloaltonetworks | pa-501 |
| paloaltonetworks | pa-505 |
| paloaltonetworks | pa-510 |
| paloaltonetworks | pa-520 |
| paloaltonetworks | pa-540 |
| paloaltonetworks | pa-5410 |
| paloaltonetworks | pa-5420 |
| paloaltonetworks | pa-5430 |
| paloaltonetworks | pa-5440 |
| paloaltonetworks | pa-5445 |
| paloaltonetworks | pa-545-poe |
| paloaltonetworks | pa-5450 |
| paloaltonetworks | pa-550 |
| paloaltonetworks | pa-5540 |
| paloaltonetworks | pa-555-poe |
| paloaltonetworks | pa-5550 |
| paloaltonetworks | pa-5560 |
| paloaltonetworks | pa-5570 |
| paloaltonetworks | pa-5580 |
| paloaltonetworks | pa-560 |
| paloaltonetworks | pa-7500 |
| paloaltonetworks | pa-7500-dpc-a |
| paloaltonetworks | vm-100 |
| paloaltonetworks | vm-300 |
| paloaltonetworks | vm-50 |
| paloaltonetworks | vm-500 |
| paloaltonetworks | vm-700 |
| siemens | ruggedcom_ape1808_firmware |
| siemens | ruggedcom_ape1808 |
References
Frequently Asked Questions
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. It has a CVSS v3.1 base score of 9.8 (CRITICAL). This vulnerability is listed in CISA's Known Exploited Vulnerabilities catalog, indicating active exploitation in the wild.
How severe is CVE-2026-0300? +
CVE-2026-0300 has a CVSS v3.1 score of 9.8 out of 10, rated CRITICAL. This is a critical vulnerability that should be patched immediately. The EPSS score is 0.0454, placing it in the 1th percentile for exploitation probability.
What products are affected by CVE-2026-0300? +
CVE-2026-0300 affects products from paloaltonetworks, siemens, specifically: pa-1410, pa-1420, pa-3410, pa-3420, pa-3430, pa-3440, pa-410, pa-410r, pa-410r-5g, pa-415, pa-415-5g, pa-440, pa-445, pa-450, pa-450r, pa-450r-5g, pa-455, pa-455-5g, pa-455r-5g, pa-460, pa-501, pa-505, pa-510, pa-520, pa-540, pa-5410, pa-5420, pa-5430, pa-5440, pa-5445, pa-545-poe, pa-5450, pa-550, pa-5540, pa-555-poe, pa-5550, pa-5560, pa-5570, pa-5580, pa-560, pa-7500, pa-7500-dpc-a, pan-os, ruggedcom_ape1808, ruggedcom_ape1808_firmware, vm-100, vm-300, vm-50, vm-500, vm-700. Check the affected products table above for specific version ranges.
How do I check if I'm vulnerable to CVE-2026-0300? +
You can use Secably's free Website Scanner to check your website for known vulnerabilities. For infrastructure scanning, use the Port Scanner to identify exposed services that may be affected. Check the vendor advisories linked above for specific patch and version information.
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