CVE-2026-85926 in Windows
Summary
by MITRE • 10/14/2026
Use after free in Windows Secure Socket Tunneling Protocol (SSTP) allows an unauthorized attacker to execute code over a network.
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Analysis
by VulDB Data Team • 10/14/2026
The vulnerability described involves a use-after-free condition within the Microsoft Windows Secure Socket Tunneling Protocol, commonly referred to as SSTP. This protocol is designed to provide secure remote access by encapsulating Point-to-Point Protocol frames inside HTTPS sessions, thereby allowing traffic to traverse firewalls that might otherwise block traditional VPN protocols like PPTP or L2TP. The core technical flaw lies in the memory management logic of the SSTP service implementation. Specifically, a pointer to a previously allocated and subsequently freed memory object is accessed after its deallocation has occurred. This scenario typically arises when an application fails to properly nullify pointers following memory release or maintains stale references that are not updated during state transitions within the protocol handler. When an attacker crafts specific network packets containing malformed SSTP data, they can trigger this erroneous access pattern, leading to undefined behavior in the operating system's kernel mode execution context.
From a technical perspective, use-after-free vulnerabilities represent a critical class of memory corruption errors categorized under CWE-416 in the Common Weakness Enumeration standard. In the context of Windows networking stacks, these flaws are particularly dangerous because they often occur with high privileges and can be exploited remotely without requiring user interaction or authentication on the target system. The attacker constructs malicious SSTP packets that exploit the timing window between memory deallocation and subsequent dereference. By carefully controlling the contents of the freed memory region through further network interactions, an adversary can manipulate the data structure pointed to by the stale pointer. This manipulation allows for arbitrary code execution within the security context of the affected service, which typically runs with SYSTEM-level privileges on the host machine.
The operational impact of this vulnerability is severe, as it enables a remote attacker to gain full control over the compromised Windows system. Once code execution is achieved, the attacker can install malware, exfiltrate sensitive data, create new user accounts for persistent access, or pivot to other systems within the internal network. Because SSTP operates over standard HTTPS ports such as TCP 443, this vulnerability may bypass many perimeter security controls that allow outbound web traffic by default. The ability to execute code remotely makes this a high-severity issue according to CVSS scoring guidelines, particularly when it affects widely deployed server infrastructure or remote access gateways. Organizations relying on SSTP for secure connectivity are at significant risk if the underlying Windows components remain unpatched.
Mitigation strategies primarily involve applying the latest security updates provided by Microsoft that address this specific memory management flaw in the SSTP implementation. Administrators should ensure that all systems running vulnerable versions of Windows are patched promptly. In environments where immediate patching is not feasible, network-level mitigations can be employed to reduce exposure. This includes restricting access to SSTP services through firewall rules or intrusion prevention systems by filtering out malformed packets or limiting connections to trusted IP ranges only. Additionally, disabling the SSTP service if it is not actively required for business operations reduces the attack surface significantly. Security teams should also monitor network traffic for anomalies indicative of exploitation attempts and maintain strict adherence to least privilege principles when configuring remote access services.
This vulnerability aligns with several tactics in the MITRE ATT&CK framework, particularly those related to initial access and execution via compromised infrastructure or legitimate protocols. Attackers often leverage trusted protocols like HTTPS to evade detection, making this type of exploit effective against modern security architectures that rely on protocol whitelisting rather than deep packet inspection for all traffic types. Understanding these attack vectors is crucial for defenders who must balance connectivity requirements with robust security postures. Continuous monitoring and timely patching remain the most effective defenses against such sophisticated memory corruption vulnerabilities in network services.