External risk intelligence

Microsoft PEAP Remote Code Execution Vulnerability

CVE advisorySeverity: CRITICAL (CVSS 9.8)

CVE-2023-21690

The vulnerability involves Microsoft PEAP, a protocol typically used within local enterprise networks for authentication to internal Wi-Fi or wired networks. While it is technically network-reachable, it is generally not exposed directly to the public internet in standard deployment patterns, making external reachability possible but uncommon.

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: 3 out of 5 — possibly public-facing.

External exposure likelihood

Horizon Alert

Summary of the vulnerability and why it matters

A critical vulnerability has been identified in Microsoft's Protected Extensible Authentication Protocol (PEAP), a component used for network authentication. This issue could allow an unauthenticated attacker to remotely execute code, potentially leading to a compromise of affected systems. The main concern is confirming whether this specific authentication protocol is in use within our environment and if it is exposed in a way that could be targeted.

Unauthenticated remote code execution flaw found.
Affects network authentication protocols.
Confirm relevance and exposure in our environment.

Attack Path

How an attacker could exploit the issue

An attacker could exploit this vulnerability by sending a specially crafted request over the network to a vulnerable system. This could lead to remote code execution, allowing the attacker to take control of the affected system. The vulnerability is related to the Microsoft Protected Extensible Authentication Protocol (PEAP).

No special access required.
Triggered by network request.
Allows full system control.

Live Threat

Current exploitation, exposure, and threat context

This vulnerability in Microsoft's Protected Extensible Authentication Protocol (PEAP) could allow an unauthenticated attacker to execute arbitrary code on affected systems. This could occur when a vulnerable system attempts to authenticate to a malicious or compromised PEAP server. The confidentiality, integrity, and availability of the system could be impacted.

System data and services are at risk.
Remote unauthenticated code execution is possible.
Complete system compromise could occur.

Operational Fix

Recommended remediation, mitigation, and detection steps

This critical vulnerability in Microsoft's Protected Extensible Authentication Protocol (PEAP) impacts a wide range of Windows operating systems and servers. Ownership typically falls to the infrastructure or platform teams responsible for network authentication services, in coordination with security and system owners. The immediate first step is to identify all instances of affected Windows systems, determine their exposure to attack, and confirm the accountable owner for remediation planning.

Infrastructure and platform teams own the fix.
Verify system exposure and accountable owner.
Plan and execute 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.

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Frequently asked questions

What is Microsoft PEAP and why is it used?

PEAP, or Protected Extensible Authentication Protocol, is a Microsoft authentication component. It is primarily used to securely connect computers to enterprise Wi-Fi or wired networks by validating credentials between a device and an authentication server.

What does CWE-122 mean in the context of CVE-2023-21690?

CWE-122 refers to a heap-based buffer overflow. In simple terms, this vulnerability occurs when the software tries to store more data in a specific area of memory (the heap) than it is designed to hold. This memory corruption can allow an attacker to overwrite adjacent data, potentially leading to unauthorized remote code execution.

How is this vulnerability triggered?

An attacker triggers this flaw by sending a specially crafted request over the network. This often happens when a vulnerable Windows system attempts to authenticate with a malicious or compromised server. Simply being on a network is the primary requirement; no existing user account or special authentication is needed to initiate the attack.

Do I need to worry about internet exposure for CVE-2023-21690?

According to Halo Surface Signal, this vulnerability is most often found within internal enterprise networks where PEAP manages local authentication. While it is theoretically reachable via the network, standard deployments are rarely exposed directly to the public internet, which limits the attack surface for external actors.

What are the first steps to address this issue?

Your first priority is to create an inventory of all Windows systems in your environment that are running the affected versions. Once you have identified these assets, coordinate with your infrastructure or platform teams to assess how these systems are connected to the network and prioritize remediation based on that exposure.

References

msrc.microsoft.com/update-guide/vulnerability/CVE-2023-21690

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.