External risk intelligence

Microsoft PEAP Remote Code Execution Vulnerability

CVE advisorySeverity: CRITICAL (CVSS 9.8)

CVE-2023-21689

This vulnerability affects PEAP, which is primarily used for authentication within internal network segments like RADIUS/802.1X for corporate Wi-Fi or VPNs. Direct exposure to the public internet is rare and typically restricted by infrastructure controls, making it unlikely for this service to be exposed to external attack vectors.

Remote Code Execution

Microsoft Windows 10 1507

before 10.0.10240.19747before 10.0.14393.5717before 10.0.17763.4010before 10.0.19042.2604before 10.0.19044.2604before 10.0.19045.2604before 10.0.22000.1574before 10.0.22621.1265r2

Halo Surface Signal: 2 out of 5 — less likely to be public-facing.

External exposure likelihood

Horizon Alert

Summary of the vulnerability and why it matters

A vulnerability has been identified in Microsoft's Protected Extensible Authentication Protocol (PEAP) that could allow for remote code execution. This protocol is used for secure authentication, and the vulnerability could potentially be exploited to compromise systems. The main concern is to confirm whether our environment is affected and to what extent.

Authentication protocol has a remote code execution flaw.
Critical flaw impacts network access security.
Confirm relevance and exposure to affected systems.

Attack Path

How an attacker could exploit the issue

An attacker could exploit this vulnerability by sending a specially crafted request to a vulnerable system that handles Protected Extensible Authentication Protocol (PEAP) traffic. Successful exploitation could allow an attacker to execute arbitrary code on the affected system.

No authentication or network access needed.
Triggered by a crafted PEAP request.
Enables remote code execution.

Live Threat

Current exploitation, exposure, and threat context

This vulnerability could allow an unauthenticated attacker to execute arbitrary code on affected systems when PEAP is used. This could lead to a compromise of the system's integrity and confidentiality.

System integrity and confidentiality.
Exploited over the network when PEAP is used.
Full system compromise.

Operational Fix

Recommended remediation, mitigation, and detection steps

This vulnerability impacts Microsoft's Protected Extensible Authentication Protocol (PEAP), which is commonly used for network authentication. Responsibility for addressing this likely falls to infrastructure or platform teams managing authentication services, in coordination with network and security teams for exposure assessment. The first practical step is to identify all systems utilizing PEAP, determine their network exposure and business criticality, and then confirm ownership to prioritize remediation efforts.

Identify PEAP usage and ownership.
Verify network exposure and criticality.
Plan remediation based on risk.

Supplementary metadata

CVSS vector

Validate whether this threat affects your internet-facing exposure.

Halo Threat Intelligence helps prioritize remediation with Halo Surface Signal and H/A/L/O context. Start exposure validation with a free external attack surface trial.

Free EASM Trial See How Signal Works

Frequently asked questions

What is the software affected by CVE-2023-21689?

This vulnerability impacts Microsoft’s Protected Extensible Authentication Protocol (PEAP), a service integrated into a wide range of Windows 10, Windows 11, and Windows Server operating systems. PEAP is used to provide secure authentication for network access, allowing users or devices to verify their identity when connecting to corporate resources like Wi-Fi networks or VPNs.

What does this vulnerability actually do?

CVE-2023-21689 is categorized as a heap-based buffer overflow, identified as CWE-122. In plain terms, this means the software fails to properly manage data stored in a specific memory area when processing network requests. An attacker can leverage this flaw to send specially crafted data that overwhelms the memory, potentially allowing them to run unauthorized code on the targeted system.

How is this vulnerability triggered?

An attacker can trigger this vulnerability by sending a malicious request to a system configured to process PEAP traffic. Because this is a network-based flaw, it does not require the attacker to have valid user credentials or physical access to the machine. It is important to note that this issue is specific to the handling of PEAP communications; it does not impact systems or services that do not use this protocol for authentication.

Is my environment at risk from this flaw?

Halo Surface Signal indicates that direct public internet exposure for this vulnerability is unlikely. Because PEAP is typically used within internal network segments—such as RADIUS or 802.1X environments for managed Wi-Fi—the risk is generally higher for internal systems rather than those directly facing the open internet. You should focus your assessment on servers or infrastructure components that act as authentication gateways.

What steps should I take if I use this technology?

Your first priority is to locate all internal systems in your environment that are actively running PEAP services. Once you have identified these assets, verify their current patch status against the affected Windows versions listed in the advisory. Coordinate with your infrastructure and network teams to confirm ownership and prioritize updates for those systems, specifically focusing on critical authentication infrastructure.

References

msrc.microsoft.com/update-guide/vulnerability/CVE-2023-21689

Written by Nicholas Merritt

Nicholas Merritt is VP of Security Solutions at Halo Security. With more than 25 years across application security, vulnerability prioritization, and offensive security, he helps teams translate threat data into practical exposure validation and remediation focus. He authors Halo Threat Intelligence CVE advisories using Halo Surface Signal and H/A/L/O context to prioritize internet-facing risk.