External risk intelligence

Microsoft QUIC Heap-Based Buffer Overflow Leads to Network Code Execution

CVE advisorySeverity: CRITICAL (CVSS 9.8)

CVE-2026-105016

Microsoft QUIC is a transport layer protocol implementation used extensively in internet-facing web servers, APIs, and edge services. Because QUIC is designed to handle network traffic for public-facing applications and services, the underlying library is commonly exposed to, and reachable from, the public internet in standard deployment patterns.

Buffer Overflow

Halo Surface Signal: 4 out of 5 — likely to be public-facing.

External exposure likelihood

Horizon Alert

Summary of the vulnerability and why it matters

This advisory details a critical vulnerability in Microsoft's QUIC implementation, a network communication protocol. The flaw could permit an unauthenticated attacker to remotely execute arbitrary code over a network, posing a significant risk to services that utilize this technology. The main concern is to confirm if our environment utilizes this specific Microsoft QUIC component and assess potential exposure.

Vulnerability in Microsoft QUIC allows remote code execution.
Affects widely used internet-facing services and applications.
Confirm relevance and exposure of Microsoft QUIC.

Attack Path

How an attacker could exploit the issue

An attacker could exploit this vulnerability over a network without needing any special privileges or user interaction. By sending specially crafted data to the vulnerable Microsoft QUIC component, an attacker could trigger a heap-based buffer overflow, potentially leading to arbitrary code execution.

Network access is required.
Specially crafted data triggers overflow.
Arbitrary code execution possible.

Live Threat

Current exploitation, exposure, and threat context

A heap-based buffer overflow in Microsoft QUIC could allow an unauthenticated attacker to execute arbitrary code over a network connection. This could affect systems that use Microsoft QUIC for network communication and are exposed to the internet, potentially leading to a compromise of the underlying system.

System code execution.
Network-based code execution.
Complete system compromise.

Operational Fix

Recommended remediation, mitigation, and detection steps

This critical vulnerability in Microsoft QUIC, an internet-facing transport protocol, requires immediate attention from teams managing public-facing applications and services. The first practical step is to identify all instances of Microsoft QUIC, determine their network reachability and business criticality, locate the accountable system owners, and then prioritize remediation efforts based on potential exposure.

Platform and infrastructure teams own this issue.
Verify network exposure and business criticality first.
Plan coordinated patching or vendor engagement.

Supplementary metadata

CVSS vector

Validate whether this threat affects your internet-facing exposure.

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Frequently asked questions

What is Microsoft QUIC and what is it used for?

Microsoft QUIC is a transport layer network protocol implementation. It is primarily used to facilitate high-performance, low-latency communication for web servers, APIs, and edge services that rely on the QUIC standard to move data across networks efficiently.

What does CVE-2026-105016 mean for system security?

This vulnerability is a heap-based buffer overflow, classified as CWE-122. It occurs when a program writes more data to a specific memory area than it can hold. Because of this flaw, an attacker could potentially overwrite adjacent memory to execute unauthorized code on the system.

How is this Microsoft QUIC vulnerability triggered?

An attacker triggers the flaw by sending specially crafted network data to the QUIC component. The vulnerability requires network access to function; it is not triggered by local file operations or internal system commands that do not involve external network traffic.

Is my infrastructure at risk from CVE-2026-105016?

Halo Surface Signal indicates that because Microsoft QUIC is frequently deployed in internet-facing web servers and public-facing APIs, it is often reachable from the public internet. If your services use this protocol to handle external traffic, they are more likely to be reachable by an attacker.

What should I do first to address this threat?

Start by identifying every system in your environment that utilizes the Microsoft QUIC component. Once inventoried, determine which of those instances are exposed to the network and evaluate their business criticality to prioritize your patching or vendor update schedule.

References

msrc.microsoft.com/update-guide/vulnerability/CVE-2026-105016

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.