CVE-2024-21762 is a critical (CVSS 9.8) out-of-bounds write (CWE-787) in the SSL VPN functionality of Fortinet FortiOS and FortiProxy, allowing an unauthenticated remote attacker to execute unauthorized code or commands by sending specifically crafted requests to the vulnerable service. No authentication or user interaction is required, and network access to the SSL VPN interface is the only precondition. Organizations running affected FortiOS versions (on FortiGate appliances) or any affected FortiProxy version are exposed, particularly where the SSL VPN is internet-facing. The flaw is actively exploited: it was added to CISA's Known Exploited Vulnerabilities catalog on 2024-02-09 with ransomware use noted, EPSS puts the 30-day exploitation probability at 84.3%, and public scans suggest roughly 150,000 internet-exposed Fortinet devices may be impacted.
What to do: Upgrade FortiOS and FortiProxy to fixed releases outside the affected ranges per Fortinet's advisory, prioritizing internet-facing devices; as an interim mitigation, disable SSL VPN (or SSL VPN web mode) where it is not required, per vendor and CISA guidance. After patching, check for signs of compromise and rotate credentials, since Fortinet has warned that attackers retained access to FortiGate devices post-patching. The flaw is in CISA KEV with known ransomware use, so treat this as an urgent patching priority.
Affected
Fortinet FortiOS
7.4.0 through 7.4.2, 7.2.0 through 7.2.6, 7.0.0 through 7.0.13, 6.4.0 through 6.4.14, 6.2.0 through 6.2.15, 6.0.0 through 6.0.17
Fortinet FortiProxy
7.4.0 through 7.4.2, 7.2.0 through 7.2.8, 7.0.0 through 7.0.14, 2.0.0 through 2.0.13, 1.2.0 through 1.2.13, 1.1.0 through 1.1.6, 1.0.0 through 1.0.7
Estimated exposure
mass≈150,000 internet-exposed FortiGate/FortiProxy devices (public internet-wide scans) — Public internet-exposure scans cited in reporting identified roughly 150,000 potentially affected devices, and the true figure is likely higher because Fortinet's installed base is large and many appliances expose SSL VPN only to VPN…
Order-of-magnitude estimate by the model from install counts, market share and public scan data it knows; verify before quoting.
Description
A out-of-bounds write in Fortinet FortiOS versions 7.4.0 through 7.4.2, 7.2.0 through 7.2.6, 7.0.0 through 7.0.13, 6.4.0 through 6.4.14, 6.2.0 through 6.2.15, 6.0.0 through 6.0.17, FortiProxy versions 7.4.0 through 7.4.2, 7.2.0 through 7.2.8, 7.0.0 through 7.0.14, 2.0.0 through 2.0.13, 1.2.0 through 1.2.13, 1.1.0 through 1.1.6, 1.0.0 through 1.0.7 allows attacker to execute unauthorized code or commands via specifically crafted requests
CISA Known Exploited Vulnerability
Affected
Fortinet FortiOS
Required action
Apply mitigations per vendor instructions or discontinue use of the product if mitigations are unavailable.
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.
Exposed attacker staging server reveals intrusion of Thai broadband provider 3BB via actively exploited FortiGate SSL-VPN flaw CVE-2024-21762.
Hunt.io found an open directory on server 92.63.180[.]133 holding 298 files detailing an intrusion into Triple T Broadband's 3BB brand, starting from a FortiGate 60F SSL-VPN at mail.3bb.co[.]th:10443. The actor weaponized CVE-2024-21762 (CVSS 9.8, KEV-listed since February 2024) using heap spraying and a ROP chain to gain a reverse shell. Post-exploitation included MeshCentral root-level persistence via www.ayuthayatech[.]com, Dirty COW/PwnKit privilege escalation, credential harvesting, SSH spraying against 55+ internal addresses, and log-deleting cleanup scripts; a stolen OpenVPN certificate and key from Triple T's PKI may still be valid.
Hackers exploited Fortinet CVE-2024-21762 RCE to breach Thai broadband provider 3BB, deploying MeshCentral backdoors and credential-harvesting tools across its network.
Hunt.io uncovered an intrusion staging directory in Thailand containing 298 files of custom tooling built for Triple T Broadband (3BB) and its former owner Jasmine. Initial access came via fingerprinting a FortiGate SSL-VPN appliance and exploiting CVE-2024-21762 for remote code execution, after probing CVE-2018-13379, CVE-2022-42475, and CVE-2023-27997. The actor also probed F5 BIG-IP for CVE-2021-22986, CVE-2022-1388, and CVE-2023-46747, escalated privileges with PwnKit and Dirty COW, used MeshCentral as a C2 backdoor, harvested SSH/database/SNMP/Radius credentials, deployed PHP web shells, and ran cleanup scripts to hide the intrusion.
Hunt.io found an attacker holding root access inside Thai ISP 3BB via a MeshCentral backdoor, targeting subscriber RADIUS credential databases.
Hunt.io discovered an exposed attacker server on June 3, 2026 revealing an ongoing intrusion at 3BB, one of Thailand's largest broadband providers. The attacker maintained hidden MeshCentral agents reporting to www.ayuthayatech[.]com (device group TH-3BB) and held root on internal servers. Recovered scripts sprayed passwords over SSH against more than 55 internal machines, planted web shells, added SSH keys, searched for stored credentials, and targeted RADIUS subscriber credential databases, though exfiltration was not confirmed. The toolkit included a full exploit for FortiGate SSL-VPN flaw CVE-2024-21762 against mail.3bb.co[.]th, but the initial access vector is unestablished, and a cleanup script erased logs while preserving the backdoor.