CVE-2026-83498 Lets Local Attackers Run Code Inside a Windows VBS Enclave

Microsoft has patched a Windows vulnerability that researchers used to execute attacker-selected code inside the Virtualization-Based Security enclave supporting Enhanced Phishing Protection.

The flaw, tracked as CVE-2026-83498, affects several Windows 11 releases and Windows Server 2025. Microsoft released its advisory and fix on September 8, 2026. Doyensec published its proof-of-concept research on October 13, 2026.

Exploitation requires an attacker to have code already running locally with low privileges. No user interaction is needed, but this is not a remote attack. Doyensec’s laboratory demonstration defeated the enclave’s isolation controls; it did not show the theft of a Windows password.

A four-byte write opens the way into the enclave

The affected component is SFAPE.dll, which contains the VBS enclave used by Enhanced Phishing Protection in Microsoft Defender SmartScreen. The security feature can warn users when they enter their Windows sign-in password in an unsafe location.

According to reporting on Doyensec’s research, Windows stores a hashed representation of the sign-in password inside the enclave for later comparisons. On Windows 11, the enclave is loaded by lsass.exe, a process running as SYSTEM.

VBS enclave memory resides in Virtual Trust Level 1, or VTL1, separating it from ordinary VTL0 code. The vulnerability allowed locally running attacker code to undermine that boundary through a chain of two weaknesses.

A repeated call to the enclave’s initialization function could write a fixed four-byte error value to an address selected by the caller. Unlike the initial call, the second invocation did not perform the same address validation. Doyensec characterized this primitive as limited rather than a general-purpose arbitrary write.

Researchers nevertheless found a consequential target: a value used by the enclave to determine whether memory belongs to the enclave or its host. Corrupting that value disabled a safety check. A separate timing flaw could then trigger a controlled wipe and redirect the enclave’s lookup of a stored object.

The resulting read-and-write capability allowed the researchers to replace the table governing which code the enclave could execute. Their proof of concept ultimately ran attacker-chosen code within the protected environment.

Microsoft’s security advisory describes the underlying weakness as an untrusted pointer dereference and says an attacker could leak data from the target enclave or execute code in its context. NVD maps the issue to CWE-822.

The CVSS 3.1 base score is 7.8, with the vector:

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

Microsoft lists the maximum severity as Critical. Its temporal score is 6.8, reflecting unproven exploit maturity and the availability of an official fix.

Affected Windows versions and fixed builds

NVD identifies the following build thresholds:

For Windows 11 24H2 and 25H2, the correction was distributed through the September 8, 2026 cumulative update KB5124008. Administrators should verify that devices have reached at least the relevant fixed build rather than relying only on the displayed Windows release name.

Doyensec’s binary comparison found that the updated enclave validates the destination address before performing the problematic write. Microsoft also tightened the function involved in the timing condition.

The update additionally introduces a policy that prevents the vulnerable SFAPE enclave from loading. No separate workaround is required according to the reporting; installing the applicable cumulative update is the prescribed action.

Microsoft’s exploitation assessment predates the public research

At the original advisory publication on September 8, 2026, Microsoft marked CVE-2026-83498 as not publicly disclosed and not exploited, with an assessment of “Exploitation Less Likely.” The advisory was last revised on September 21, 2026, for an acknowledgment change.

Those assessments therefore predate Doyensec’s October 13 publication. The available research demonstrates technical exploitability in a lab, not exploitation against users in the wild.

The practical consequence is also narrower than password compromise. Although the vulnerable enclave handles password-related information, Doyensec did not demonstrate extraction of a user’s password. The confirmed research outcome was code execution inside the enclave after a local attacker had already gained the ability to run code on the machine.

Researchers flag a broader enclave-loading concern

Doyensec says Windows does not have a general blocklist for vulnerable enclaves comparable to its vulnerable-driver blocklist. The new policy reportedly blocks the old SFAPE file specifically rather than preventing every previously vulnerable enclave from loading.

As an example, the researchers said an older Microsoft Edge enclave associated with CVE-2023-36880 could still be loaded. That issue affected prefs_enclave_x64.dll, where insufficient pointer validation enabled reads and writes within enclave memory. Its GitHub Security Advisory records that it was reported on 08/29/2023, fixed on 11/27/2023 and disclosed on 12/14/2023.

The claim that this older enclave remains loadable comes from Doyensec’s analysis. It does not change the immediate remediation for CVE-2026-83498: Windows 11 and Windows Server administrators should deploy the applicable September 8, 2026 update and confirm that systems meet or exceed the fixed build listed for their release.