CVE-2026-70465 in FortiClientWindows
Summary
by MITRE • 08/12/2026
A buffer copy without checking size of input ('classic buffer overflow') vulnerability in Fortinet FortiClientWindows 7.4.0 through 7.4.3, FortiClientWindows 7.2.0 through 7.2.11 may allow an unauthenticated attacker in a position to alter or craft DNS responses to the targeted host to execute arbitrary code via malicious packets.
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Analysis
by VulDB Data Team • 10/20/2026
This vulnerability represents a classic buffer overflow flaw that exists within Fortinet FortiClient Windows versions ranging from 7.4.0 through 7.4.3 and 7.2.0 through 7.2.11. The security weakness stems from inadequate input validation during DNS response processing, creating an opportunity for malicious actors to exploit the system through crafted network packets. The vulnerability operates at the network layer where DNS resolution occurs, making it particularly dangerous as it can be triggered without requiring authentication credentials. This type of buffer overflow falls under CWE-121 which specifically addresses stack-based buffer overflow conditions, and aligns with ATT&CK technique T1059.007 for command and scripting interpreter. The flaw allows an unauthenticated attacker positioned within the network to manipulate DNS responses destined for targeted hosts, potentially enabling remote code execution through carefully crafted malicious packets that exceed the allocated buffer space.
The operational impact of this vulnerability extends beyond simple code execution as it fundamentally compromises the integrity of DNS resolution processes within the FortiClient environment. When an attacker successfully exploits this weakness, they can inject malicious content into DNS responses that will be processed by vulnerable FortiClient installations. This creates a persistent threat vector where attackers can redirect network traffic, intercept communications, or establish footholds within the targeted network infrastructure. The vulnerability's exploitation requires minimal privileges and can be executed remotely, making it particularly attractive to threat actors seeking broad system compromise. The affected versions represent a significant portion of FortiClient deployments, amplifying the potential attack surface and organizational impact.
Mitigation strategies for this vulnerability should prioritize immediate patching of all affected FortiClient Windows installations to version 7.4.4 or later where the buffer overflow has been addressed. Network segmentation and monitoring should be implemented to detect anomalous DNS traffic patterns that may indicate exploitation attempts. Implementing DNS security extensions and configuring proper access controls on DNS servers can help reduce the attack surface. Organizations should also deploy intrusion detection systems with signature-based detection for known exploit patterns related to this vulnerability. The mitigation approach aligns with ATT&CK tactics T1590 for reconnaissance and T1071 for application layer protocol usage, requiring both defensive measures and monitoring capabilities to prevent successful exploitation attempts.
The root cause of this vulnerability demonstrates a failure in proper input validation and memory management within the DNS processing module of FortiClient Windows. This type of flaw typically occurs when developers assume that input data will remain within expected bounds without implementing adequate bounds checking mechanisms. The vulnerability's classification as a buffer overflow indicates that the application fails to verify that incoming DNS response data fits within allocated memory buffers, creating opportunities for stack corruption and arbitrary code execution. Security best practices dictate that all input should be validated regardless of source or trust level, particularly when processing network protocols like DNS where attackers can craft malicious payloads. Organizations should implement comprehensive code review processes and static analysis tools to identify similar vulnerabilities in their software development lifecycle, preventing recurrence of such memory safety issues.