Rapid7: Attackers exploit authentication bypass flaw in the wild, meaning more emergency patching for PAN-OS users
Palo Alto customers are being been told to patch yet another internet-facing security flaw after researchers caught attackers bypassing GlobalProtect authentication and gaining unauthorized VPN access.
The flaw, tracked as CVE-2026-0257, affects PAN-OS deployments using GlobalProtect authentication override cookies under specific configurations.
Palo Alto disclosed the bug on May 13 and initially assigned it a medium-severity rating, saying it was aware of attempts to exploit it but had not observed any malicious exploitation.
That assessment has not aged well.
Security boffins at Rapid7 said they observed successful exploitation across multiple customer environments dating back to at least May 17 and validated the attack technique using its own proof-of-concept testing. Attackers established unauthorized VPN sessions on vulnerable systems, potentially granting access to internal corporate networks without legitimate credentials, it added.
Rapid7's analysis suggests the flaw comes down to how PAN-OS trusts authentication override cookies. In certain deployments, hackers can create their own cookies and have the firewall accept them as legitimate. The risk is highest where the same certificate is used for both HTTPS services and authentication override cookies, giving the baddies access to the information needed to generate convincing fakes.
Rapid7 said it observed multiple waves of activity targeting vulnerable devices. In some cases, cybercrims successfully obtained VPN IP addresses and network access, but the company said it didn’t observe evidence of successful lateral movement following initial access in the incidents it investigated.
The flaw has now landed in CISA's Known Exploited Vulnerabilities catalog, with federal agencies given until June 1 to patch or otherwise secure affected systems. Palo Alto has also revised its advisory, elevating the severity rating and attaching its highest urgency label. Fixes are available for supported releases.
"Palo Alto Networks has become aware of limited exploit attempts on unpatched PAN-OS devices without mitigations applied," the firm said in an update.
The latest PAN-OS headache arrives less than a month after another Palo Alto emergency. In May, state-backed attackers were found exploiting CVE-2026-0300, a critical remote code execution flaw in the PAN-OS User-ID Authentication Portal, before patches became widely available.
Organizations running vulnerable GlobalProtect gateways now face a familiar choice: patch quickly or find out whether someone else gets there first.®