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Fortinet FortiWeb was found to contain a remotely exploitable denial-of-service flaw, tracked as CVE-2026-39811 and published as ZDI-26-265. The bug is an integer overflow in cgi_buf_alloc during HTTP request handling that can be triggered by a crafted request, causing the server to enter an infinite loop and lose availability. The issue requires authentication, carries a CVSS 6.5 rating, and was reported to Fortinet by Jason McFadyen of Trend Research before Fortinet released a fix.
The disclosure lands against a broader backdrop of sustained attacker interest in Fortinet edge technologies. SANS Internet Storm Center previously reported active scanning tied to Fortinet FortiOS and CVE-2024-21762, underscoring how quickly Fortinet vulnerabilities can attract reconnaissance and exploitation attempts once details emerge. For defenders, the combined picture is clear: apply Fortinet updates promptly, review exposure of management and HTTP interfaces, and monitor for abnormal request patterns targeting Fortinet appliances.
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The Zero Day Initiative publicly disclosed the Fortinet FortiWeb vulnerability, describing it as a remotely exploitable but authenticated denial-of-service issue with CVSS 6.5. The advisory stated that crafted requests can force the server into an infinite loop and impact availability.
Fortinet released an update to address the FortiWeb denial-of-service flaw involving an integer overflow in cgi_buf_alloc during HTTP request handling. The fix was issued before public disclosure as part of coordinated vulnerability reporting.
Jason McFadyen of Trend Research reported an integer overflow vulnerability in Fortinet FortiWeb to the vendor. The flaw, later assigned CVE-2026-39811 and ZDI-26-265, could let an authenticated remote attacker trigger an infinite loop and denial of service via crafted HTTP requests.
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Fortinet has disclosed multiple vulnerabilities in its FortiWeb web application firewall, including a critical OS command injection flaw tracked as CVE-2025-64446 and another actively exploited vulnerability, CVE-2025-58034. These vulnerabilities allow authenticated attackers to execute unauthorized code or commands on affected FortiWeb systems via crafted HTTP requests or CLI commands. Fortinet has observed exploitation of these flaws in the wild and has released security updates to address the issues, urging customers to upgrade to the latest versions to mitigate risk. The vulnerabilities impact several FortiWeb versions, and Fortinet has credited researchers from Trend Micro for responsible disclosure. The U.S. Cybersecurity and Infrastructure Security Agency (CISA) has responded by mandating that all federal civilian agencies patch CVE-2025-64446 within seven days, highlighting the severity and active exploitation of the bug. Security researchers have noted that attackers are using HTTP POST requests to create new admin-level accounts on exposed devices, and CISA has recommended disabling HTTP/HTTPS on internet-facing interfaces if immediate patching is not possible. Fortinet has communicated directly with affected customers and emphasized the importance of prompt remediation to prevent further compromise of FortiWeb deployments.
Jul 23, 2026
Fortinet has disclosed two significant vulnerabilities in its FortiWeb product, CVE-2025-58034 and CVE-2025-64446, both of which have been actively exploited in the wild. The first, CVE-2025-58034, is a medium-severity OS command injection flaw that allows authenticated attackers to execute unauthorized code via crafted HTTP requests or CLI commands. The second, CVE-2025-64446, is a critical vulnerability that can be chained with the first to facilitate authentication bypass and further command injection. Fortinet has released patches in version 8.0.2 to address these issues, but the company has faced criticism for its handling and staggered disclosure of the flaws, with some suggesting the delay was to allow customers time to patch before publicizing the risks. Security researchers, including Orange Cyberdefense, have observed several exploitation campaigns leveraging these vulnerabilities, raising concerns about the potential for widespread compromise of FortiWeb deployments. The U.S. CISA has added the new Fortinet FortiWeb flaw to its Known Exploited Vulnerabilities catalog, underscoring the urgency for organizations to apply the latest patches. The incidents highlight ongoing risks in supply chain and critical infrastructure security, as attackers increasingly target widely deployed security appliances with zero-day exploits.
Jun 29, 2026
Attackers are actively exploiting a command injection vulnerability in Fortinet FortiWeb, tracked as CVE-2025-58034, which allows authenticated users to execute unauthorized code on affected systems. The flaw, caused by improper neutralization of special elements in the `policy_scripting_post_handler` method, enables code execution as root via crafted HTTP requests or CLI commands. Fortinet released patches for affected FortiWeb versions between October 23 and 31, 2025, but did not publicly disclose the vulnerability at the time. The issue was privately reported by a Trend Micro researcher, and both Fortinet and CISA have confirmed active exploitation, with CISA adding the CVE to its Known Exploited Vulnerabilities catalog and mandating rapid remediation for US federal agencies. Security researchers warn that proof-of-concept code for CVE-2025-58034 may soon be publicly available, increasing the risk of widespread attacks. There is currently no workaround for this vulnerability, and organizations are urged to upgrade to the fixed FortiWeb versions immediately and check for signs of compromise. The vulnerability requires authentication to exploit, but successful exploitation grants attackers root-level access. The disclosure timeline shows the vulnerability was reported in June 2025 and publicly disclosed in November 2025, with coordinated advisories from both Fortinet and the Zero Day Initiative.
Jun 29, 2026