Threat actors have begun to exploit two newly disclosed security flaws in Fortinet FortiGate devices, less than a week after public disclosure.
Cybersecurity company Arctic Wolf said it observed active intrusions involving malicious single sign-on (SSO) logins on FortiGate appliances on December 12, 2025. The attacks exploit two critical authentication bypasses (CVE-2025-59718 and CVE-2025-59719, CVSS scores: 9.8). Patches for the flaws were released by Fortinet last week for FortiOS, FortiWeb, FortiProxy, and FortiSwitchManager.
“These vulnerabilities allow unauthenticated bypass of SSO login authentication via crafted SAML messages, if the FortiCloud SSO feature is enabled on affected devices,” Arctic Wolf Labs said in a new bulletin.
It’s worth noting that while FortiCloud SSO is disabled by default, it is automatically enabled during FortiCare registration unless administrators explicitly turn it off using the “Allow administrative login using FortiCloud SSO” setting in the registration page.
In the malicious activity observed by Arctic Wolf, IP addresses associated with a limited set of hosting providers, such as The Constant Company llc, Bl Networks, and Kaopu Cloud Hk Limited, were used to carry out malicious SSO logins against the “admin” account.
Following the logins, the attackers have been found to export device configurations via the GUI to the same IP addresses.
A spokesperson for Arctic Wolf Labs told The Hacker News that the campaign is still in its early stages, adding that only a relatively small proportion of monitored networks have been affected.
“Our investigation is ongoing into the origin and nature of this threat activity, and we are not able to attribute the attacks to any specific threat actor group at this time,” it added. “So far, the pattern of activity has appeared to be opportunistic in nature.”
In light of ongoing exploitation activity, organizations are advised to apply the patches as soon as possible. As mitigations, it’s essential to disable FortiCloud SSO until the instances are updated to the latest version and limit access to management interfaces of firewalls and VPNs to trusted internal users.
“Although credentials are typically hashed in network appliance configurations, threat actors are known to crack hashes offline, especially if credentials are weak and susceptible to dictionary attacks,” Arctic Wolf said.
Fortinet customers who find indicators of compromise (IoCs) consistent with the campaign are recommended to assume compromise and reset hashed firewall credentials stored in the exfiltrated configurations.
Update
The U.S. Cybersecurity and Infrastructure Security Agency (CISA), on December 16, 2025, added CVE-2025-59718 to its Known Exploited Vulnerabilities (KEV) catalog, requiring Federal Civilian Executive Branch (FCEB) agencies to apply the fixes by December 23, 2025.
