CVE-2026-71332: Windows SSTP Use After Free Vulnerability

CVE-2026-71332 Overview

CVE-2026-71332 is a use-after-free vulnerability in the Windows Secure Socket Tunneling Protocol (SSTP) implementation. An authorized local attacker can exploit the flaw to elevate privileges on affected Windows systems. The weakness is categorized as [CWE-416] (Use After Free) and stems from the SSTP component referencing freed memory during protocol processing.

Successful exploitation grants an attacker higher privileges than initially assigned, enabling further compromise of the host. Microsoft addressed the issue through its security update program and published guidance in the Microsoft Security Response Center advisory.

Critical Impact
Local privilege escalation to a higher trust boundary through corruption of freed memory in the SSTP service.

Affected Products

Microsoft Windows (versions listed in the Microsoft Security Update Guide entry for CVE-2026-71332)
Windows Secure Socket Tunneling Protocol (SSTP) component
Refer to the Microsoft Security Update CVE-2026-71332 advisory for the authoritative product list

Discovery Timeline

2026-09-08 - CVE-2026-71332 published to NVD
2026-09-09 - Last updated in NVD database

Technical Details for CVE-2026-71332

Vulnerability Analysis

The vulnerability resides in the Windows implementation of the Secure Socket Tunneling Protocol, a VPN protocol that transports PPP traffic through an SSL/TLS channel. The defect is a use-after-free condition, meaning the SSTP code continues to reference a heap object after that object has been released.

An attacker with valid local credentials can trigger the freed-object reference during SSTP request handling. When the freed allocation is replaced with attacker-controlled data, the subsequent use of the dangling pointer allows corruption of program state. This can be steered toward code execution in a higher-privileged context.

The attack complexity is high because the attacker must win a timing window between the free and the reuse. Once achieved, the impact spans confidentiality, integrity, and availability of the host.

Root Cause

The root cause is improper lifetime management of a heap allocation within the SSTP driver or service. A code path releases the object without clearing or invalidating all pointers that still reference it, leaving a dangling pointer that is later dereferenced.

Attack Vector

Exploitation requires local access and low privileges on the target host. The attacker interacts with the SSTP interface to trigger the free-then-use sequence, then sprays the heap to place controlled data in the reclaimed slot. No user interaction is required. The vulnerability manifests entirely on the affected system and does not require a network position.

No public proof-of-concept exploit code has been observed. See the Microsoft Security Update CVE-2026-71332 advisory for vendor technical detail.

Detection Methods for CVE-2026-71332

Indicators of Compromise

Unexpected crashes or bug checks referencing SSTP driver modules or the RasSstp service.
Creation of new privileged accounts or scheduled tasks by processes that originated from a low-privileged user session.
Anomalous process lineage where SYSTEM-level processes spawn from user-context SSTP interactions.

Detection Strategies

Enable Windows Error Reporting collection and centralize crash dumps to identify repeatable faults in SSTP components.
Alert on privilege changes and token manipulation events (Windows Event IDs 4672, 4673, 4674) originating from non-administrative user sessions.
Correlate SSTP configuration changes with subsequent process elevation events on the same host.

Monitoring Recommendations

Ingest endpoint telemetry into a centralized SIEM or data lake and baseline normal SSTP service behavior per host.
Monitor for repeated service restarts of RAS-related components, which can indicate exploitation attempts against use-after-free conditions.
Track patch compliance for the Microsoft security update associated with CVE-2026-71332 across the fleet.

How to Mitigate CVE-2026-71332

Immediate Actions Required

Apply the Microsoft security update referenced in the Microsoft Security Update CVE-2026-71332 advisory to all affected Windows systems.
Prioritize patching on multi-user systems, jump hosts, and endpoints where non-administrative users have interactive access.
Audit local account inventories and remove unnecessary standing user accounts that could serve as an exploitation foothold.

Patch Information

Microsoft has issued a security update through the Microsoft Security Response Center. Consult the vendor advisory for the KB numbers, applicable Windows builds, and installation guidance specific to your environment.

Workarounds

Disable the SSTP protocol on hosts that do not require it, using the Routing and Remote Access configuration to remove SSTP as an available VPN transport.
Restrict interactive and remote logon rights to trusted administrators only, reducing the population of users able to trigger the local attack path.
Enforce application control policies to block unauthorized binaries from initiating SSTP interactions on endpoints.

bash

# Configuration example: disable SSTP as an accepted VPN protocol on a Windows RRAS server
# Run in an elevated PowerShell session
Set-VpnServerConfiguration -TunnelType Ikev2
Restart-Service RemoteAccess