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Gunra Ransomware Exploits Fortinet FortiOS, FortiProxy Flaws to Breach Networks
CISA, FBI, and South Korean agencies warn Gunra ransomware, with 51 victims since April 2025, exploits Fortinet flaws for double-extortion attacks on critical infrastructure.
CISA, the FBI, and South Korean agencies warned of Gunra ransomware attacks targeting healthcare, financial services, government, and professional services worldwide. The Conti-derived operation exploits internet-facing Fortinet FortiOS and FortiProxy flaws CVE-2024-55591 and CVE-2025-24472 for initial access, then deploys double extortion with Salsa20/ChaCha20 encryption and publishes non-payers on a leak site within five to seven days. Ransomware.Live lists 51 victims since April 2025, mostly in South Korea, Brazil, Spain, Thailand, and Hong Kong. The group uses Impacket tools for SMB lateral movement and NTDS credential dumping, tampers with VDI authentication to accept a designated OTP value to bypass MFA, and launched a RaaS affiliate program in January 2026 under the new alias Golden Community.
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CISA Warns of Fortinet Heap-based Buffer Overflow Flaw Exploited in Attacks
CISA added actively exploited Fortinet CVE-2025-25249, a critical heap-based buffer overflow in FortiOS, FortiSwitchManager, and FortiSASE, to its KEV catalog.
CVE-2025-25249 is a heap-based buffer overflow (CWE-122/CWE-787) allowing unauthorized code execution by sending specially crafted packets. CISA added it to the Known Exploited Vulnerabilities catalog on September 9, 2026, with a September 12 remediation deadline for federal agencies under BOD 26-04 and mandatory forensic triage of affected environments. Internet-facing Fortinet firewalls and SASE platforms are a likely foothold for credential theft, persistence, and lateral movement; ransomware use is currently listed as unknown.
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CISA adds Log4Shell flaw to the Known Exploited Vulnerabilities Catalog
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Hackers Exploit FortiGate SSL-VPN Flaw to Breach Thai ISP and Deploy MeshCentral Backdoor
Threat actors exploited FortiOS SSL-VPN flaw CVE-2024-21762 to breach Thai ISP Triple T Broadband, gaining root-level persistence via MeshCentral agents.
Attackers exploited CVE-2024-21762, an out-of-bounds write enabling unauthenticated RCE in FortiOS SSL-VPN, against Triple T Broadband's FortiGate 60F at mail.3bb.co.th, launching a Node.js reverse shell via a ROP payload. Hunt.io uncovered the operation through an exposed staging directory at 92.63.180[.]133:8888 containing 298 files of exploits, credential-harvesting scripts, session cookies, and a device inventory. Post-compromise, the actors deployed MeshCentral agents (device group TH-3BB, C2 www.ayuthayatech.com) running as root, plus a hidden SUID backdoor at /usr/local/bin/.rc, and also targeted an internal Pentaho/Tomcat server with Ghostcat (CVE-2020-1938). A cleanup script removed logs, shell histories, and web shells while deliberately preserving the MeshCentral agent and SUID backdoor.
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U.S., U.K. and Australia Warn of Iranian Hackers Exploiting Microsoft, Fortinet Flaws
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Fortinet security advisory (AV26-898)
Canadian Cyber Centre advisory AV26-898 flags Fortinet vulnerabilities across FortiOS, FortiProxy, FortiPAM, FortiSandbox and FortiMonitorOnSight, urging administrators to apply updates
The Canadian Centre for Cyber Security relayed Fortinet PSIRT advisories (AV26-898) listing vulnerabilities affecting FortiOS 7.6.1-7.6.6, FortiProxy 7.6.2-7.6.6, FortiPAM Chrome extensions 7.4/8.0, FortiSandbox 4.4 and 5.0, FortiSandbox Cloud and PaaS 5.0.4-5.0.5, and FortiMonitorOnSight 7.2. The bulletin does not detail individual CVEs or exploitation. Administrators and users are encouraged to review the linked Fortinet advisories and apply the necessary updates.
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Hackers Actively Exploiting FortiGate Firewalls to Deploy Custom Node.js Malware
Attackers actively exploit CVE-2025-25249 in FortiGate firewalls to deploy PivotC2, a Node.js RAT that decrypts VPN and admin credentials.
SOCRadar assesses with high confidence that threat actors are actively exploiting CVE-2025-25249, a CVSS 9.8 heap buffer overflow in the cw_acd daemon (CAPWAP, UDP 5246) affecting FortiOS 6.4-7.6.3 and FortiSwitchManager 7.0.x/7.2.x. Attackers deploy fortirun.bin and PivotC2, a Node.js post-exploitation framework that harvests configurations and decrypts SSL-VPN, wireless, and admin credentials using AES-256-CBC and AES-128-GCM. Over 30,000 FortiGate IPs were scanned and 178 devices compromised, including two confirmed full intrusions of US organizations with Exchange mailbox exfiltration to Wasabi storage. STRU attributes the campaign to a Russian-speaking, financially motivated cybercrime operator.
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ZTNA Portal Improper Certificate Validation
Fortinet fixed an improper certificate validation flaw (CVSS 7.3) in FortiOS and FortiProxy Agentless ZTNA portal enabling unauthenticated man-in-the-middle attacks on backend traffic.
Fortinet advisory FG-IR-26-174 discloses an improper certificate validation vulnerability (CWE-295) in the FortiOS and FortiProxy Agentless ZTNA portal, rated CVSSv3 7.3. A remote and unauthenticated attacker can perform a man-in-the-middle attack on the communication channel between the ZTNA portal and the backend destination website. The advisory was revised on 2026-09-08.
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Null Pointer Dereference in Log Report
Fortinet patched a low-severity null pointer dereference (CVSS 2.5) in FortiOS, FortiProxy, and FortiPAM that lets authenticated attackers crash the httpsd daemon.
Fortinet advisory FG-IR-26-173 describes a NULL pointer dereference vulnerability (CWE-476) in FortiOS, FortiProxy, and FortiPAM, scored CVSSv3 2.5. An authenticated attacker can crash the httpsd daemon via crafted HTTP requests, causing a denial of service. The advisory was revised on 2026-09-08.
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Stack buffer overflow in WAD
FortiOS explicit proxy WAD daemon stack buffer overflow (CVSS 5.1) allows code execution only with Kerberos and SOCKS configured.
Fortinet advisory FG-IR-26-161 describes a stack-based buffer overflow (CWE-121) in the WAD daemon of FortiOS explicit proxy, scored CVSSv3 5.1. Exploitation requires an attacker able to bypass stack protection and ASLR, and the explicit proxy must be configured with Kerberos authentication and SOCKS enabled. If successful, it yields arbitrary code or command execution in the WAD daemon context via crafted sockets. No exploitation is reported in the advisory.
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UI DoS attack
FortiOS web interface is vulnerable to unauthenticated slow HTTP denial-of-service attacks via crafted requests (CVSS 5.0).
Fortinet advisory FG-IR-26-162 details an unbounded resource allocation flaw (CWE-770) in FortiOS, scored CVSSv3 5.0. An unauthenticated attacker can launch a slow HTTP denial-of-service attack against the FortiOS web interface using crafted HTTP requests. The advisory was revised on 2026-08-12 and does not state that exploitation has been observed.
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June 2026 CVE Landscape
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