This one went entirely under the radar for me yesterday. But it looks spicy. No-priv, un-auth.
https://security.paloaltonetworks.com/CVE-2026-0300
From Palo Alto:
Description
A buffer overflow vulnerability in the User-ID(tm) 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(tm) Authentication Portal per the best practice guidelines by restricting access to only trusted internal IP addresses.
Prisma Access, Cloud NGFW and Panorama appliances are not impacted by this vulnerability.
Product Status
| Versions | Affected | Unaffected ||:---:|:---:|:---:|| Cloud NGFW | None | All || PAN-OS 12.1 | < 12.1.4-h5< 12.1.7 | \>= 12.1.4-h5 (ETA: 05/13)>= 12.1.7 (ETA: 05/28) || PAN-OS 11.2 | < 11.2.4-h17< 11.2.7-h13< 11.2.10-h6< 11.2.12 | \>= 11.2.4-h17 (ETA: 05/28)>= 11.2.7-h13 (ETA: 05/13)>= 11.2.10-h6 (ETA: 05/13)>= 11.2.12 (ETA: 05/28) || PAN-OS 11.1 | < 11.1.4-h33< 11.1.6-h32< 11.1.7-h6< 11.1.10-h25< 11.1.13-h5< 11.1.15 | \>= 11.1.4-h33 (ETA: 05/13)>= 11.1.6-h32 (ETA: 05/13)>= 11.1.7-h6 (ETA: 05/28)>= 11.1.10-h25 (ETA: 05/13)>= 11.1.13-h5 (ETA: 05/13)>= 11.1.15 (ETA: 05/28) || PAN-OS 10.2 | < 10.2.7-h34< 10.2.10-h36< 10.2.13-h21< 10.2.16-h7< 10.2.18-h6 | \>= 10.2.7-h34 (ETA: 05/28)>= 10.2.10-h36 (ETA: 05/13)>= 10.2.13-h21 (ETA: 05/28)>= 10.2.16-h7 (ETA: 05/28)>= 10.2.18-h6 (ETA: 05/13) || Prisma Access | None | All |
Required Configuration for Exposure
This issue is applicable only to PA-Series and VM-Series firewalls that are configured to use User-ID(tm) Authentication Portal.
You can verify whether you have User-ID(tm) Authentication Portal configured in the User-ID(tm) Authentication Portal Settings page (Device > User Identification > Authentication Portal Settings -> Enable Authentication Portal).
Severity: CRITICAL, Suggested Urgency: HIGHEST
The risk is highest when you configure the User-ID(tm) Authentication Portal to enable access from the Internet or any untrusted network.CRITICAL - CVSS-BT: 9.3 /CVSS-B: 9.3 (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/AU:Y/R:U/V:C/RE:M/U:Red)
You can greatly reduce the risk of exploitation by restricting User-ID(tm) Authentication Portal access to only trusted internal IP addresses and preventing its exposure to the internet.HIGH - CVSS-BT: 8.7 /CVSS-B: 8.7 (CVSS:4.0/AV:A/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:L/SI:L/SA:N/E:A/AU:Y/R:U/V:C/RE:M/U:Red)
Exploitation Status
Limited exploitation has been observed targeting Palo Alto Networks User-ID(tm) Authentication Portals that are exposed to untrusted IP addresses and/or the public internet. Customers following standard security best practices, such as restricting sensitive portals to trusted internal networks are at a greatly reduced risk.
Exploitation Details/IOCs
Unit 42 has more details in their report.
https://unit42.paloaltonetworks.com/captive-portal-zero-day/
Starting April 9, 2026, there were unsuccessful exploitation attempts against a PAN-OS device. A week later, the attackers successfully achieved RCE against the device and injected shellcode. Following the compromise, the attackers immediately conducted log cleanup to mitigate detection by clearing crash kernel messages, deleting nginx crash entries and nginx crash records, as well as removing crash core dump files.
The attackers deployed a number of tools with root privileges four days later, before conducting Active Directory (AD) enumeration using the firewall’s service account credentials to target domain root and DomainDnsZones. Following enumeration, the attackers deleted ptrace injection evidence from the audit log and deleted the SetUserID (SUID) privilege escalation binary.
Known attackers are using and downloading the Earthworm and ReverseSocks5 tools.
67.206.213[.]86136.0.8[.]48146.70.100[.]69 (C2 Staging)149.104.66[.]84hxxp[:]//146.70.100[.]69:8000/php_sess (EarthWorm Download)hxxps[:]//github[.]com/Acebond/ReverseSocks5/releases/download/v2.2.0/ReverseSocks5-v2.2.0-linux-amd64.tar[.]gz (ReverseSocks5 Download)e11f69b49b6f2e829454371c31ebf86893f82a042dae3f2faf63dcd84f97a584 (EarthWorm)Safari/532.31 Mozilla/5.5 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/138.0.0.0 Safari/537.36 Edg/138.0.0.0 (Attacker User Agent String)/var/tmp/linuxap, /var/tmp/linuxda, /var/tmp/linuxupdate (Tunneling Tools)/tmp/.c (Unidentified Python Script)/tmp/R5, /var/R5 (ReverseSocks5)
IFIN Recommendations
- Follow above mitigation strategies
- Monitor Palo Alto service accounts for activity, particularly AD enumeration
- Wherever possible, monitor for the use of mentioned tools
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