CVE-2026-108400 – HEVC Video Extensions Remote Code Execution Vulnerability

Microsoft has released a security update on October 13, 2026, addressing CVE-2026-108400, a Critical remote code execution vulnerability affecting HEVC Video Extensions in the Microsoft Windows Codecs Library. The vulnerability is caused by an integer overflow or wraparound condition that could allow an unauthenticated attacker to execute malicious code when a user opens a specially crafted file. With low attack complexity and no privileges required, an attacker could use a malicious media file to compromise an affected system. Successful exploitation could result in unauthorized code execution, data exposure, and disruption of business operations.

CVSS Score: 8.8

SEVERITY: Not specified in the CVSS:3.1 Metrics.

Threat

The primary threat is remote code execution through malicious media content processed by vulnerable HEVC Video Extensions.

An attacker could create a specially crafted file designed to exploit the vulnerability and convince a user to open it. Once the file is processed by the affected codec, the vulnerability could potentially allow malicious code to execute on the target system.

Unlike vulnerabilities requiring an attacker to already possess credentials, this issue does not require authentication. However, it does depend on a user opening the malicious file.

This makes the vulnerability particularly concerning for organizations where employees regularly receive, download, or work with video files from external sources.

Exploits

• Publicly Disclosed: No
• Actively Exploited: No
• Public Proof-of-Concept (PoC): Not confirmed; exploit code maturity is listed as Unproven.
• Exploitability Assessment: Exploitation Less Likely

Microsoft indicates that exploitation is less likely, and the available vulnerability information does not identify any known active exploitation.

However, the vulnerability’s low attack complexity and lack of authentication requirements make malicious file delivery a potential concern.

Technical Summary

CVE-2026-108400 is an integer overflow or wraparound vulnerability, classified as CWE-190, affecting the Microsoft Windows Codecs Library and HEVC Video Extensions.

Integer overflow occurs when a calculation produces a value outside the range that a variable can represent. When this happens, the resulting value may wrap around or become incorrect, potentially causing software to handle memory or data in an unsafe manner.

In this case, an attacker could create a specially crafted media file that triggers the vulnerability when processed by the affected HEVC codec.

If exploitation succeeds, the attacker could potentially execute unauthorized code on the affected system. The precise internal exploitation mechanism and execution privileges are not specified in the vulnerability details.

The CVSS v3.1 metrics identify several important characteristics:

• Attack Vector: Network, indicating that malicious content can be delivered remotely.
• Attack Complexity: Low, meaning exploitation does not require unusually complex conditions.
• Privileges Required: None, meaning the attacker does not need an authenticated account.
• User Interaction: Required, because the victim must open a specially crafted file.
• Scope: Unchanged, meaning the impact remains within the affected security authority.
• Confidentiality: High, indicating potentially serious exposure of sensitive information.
• Integrity: High, indicating the possibility of unauthorized modification of data or resources.
• Availability: High, indicating potentially significant service disruption.

Successful exploitation could allow an attacker to execute malicious programs, access sensitive information, modify files, or interfere with normal operations.

Exploitability

Affected products include:

• HEVC Video Extensions: Update build 2.4.87.0.
• HEVC Video Extensions for Licensed Applications: Update build 2.4.85.0.
• HEVC Video Extensions from Device Manufacturer: Update builds 2.4.86.0 or 2.5.25.0, depending on the affected system.
• Windows 10: Versions 1809, 21H2, and 22H2.
• Windows 11: Versions 23H2, 24H2, 25H2, and 26H1.
• Windows Server: 2019, 2022, and 2025, including listed Server Core installations.

The listed builds are security update versions, not confirmed vulnerable-version boundaries.

An attacker could attempt exploitation by convincing a user to open a specially crafted file that is processed by the vulnerable HEVC codec. No authentication is required.

Business Impact

CVE-2026-108400 creates a potentially serious security risk for organizations using Windows systems to process video files and other media content.

Video files are commonly exchanged through email, collaboration platforms, cloud storage, and business applications. Attackers could potentially disguise malicious content as legitimate media and use normal file-sharing activities to deliver an exploit.

Because the vulnerability requires no attacker authentication and has low attack complexity, a successful social engineering attempt could result in unauthorized code execution.

Potential business consequences include:

• Unauthorized System Compromise: Attackers could execute malicious code on affected Windows devices.
• Sensitive Data Exposure: Confidential business files, customer information, or internal documents could potentially be accessed.
• Malware Deployment: Compromised systems could be used to install ransomware, spyware, or other malicious software.
• Operational Disruption: Affected workstations or business applications could become unavailable.
• Lateral Movement: Attackers could potentially use a compromised endpoint to target other systems within the organization.
• Financial and Reputational Damage: Successful attacks could lead to downtime, recovery costs, and loss of customer confidence.

“A video file may look harmless, but when the software processing it is vulnerable, one click could put an entire business system at risk.”

Workaround

Until the official security update can be deployed, organizations should consider the following risk-reduction measures:

• Avoid opening video files from unknown or untrusted sources.
• Restrict the downloading and opening of suspicious media attachments.
• Remove or disable HEVC Video Extensions where they are not required and doing so is operationally feasible.
• Use endpoint protection and email security controls to detect suspicious files.
• Apply the appropriate HEVC Video Extensions security updates promptly.

These measures may reduce exposure but are not confirmed fixes for the underlying vulnerability.

Urgency

CVE-2026-108400 carries a Critical maximum severity rating and a CVSS v3.1 base score of 8.8, reflecting the potentially serious consequences of successful remote code execution.

The vulnerability is particularly concerning because it requires no attacker authentication, has low attack complexity, and can potentially be triggered when a user opens a specially crafted file.

Although Microsoft considers exploitation less likely and reports no known active exploitation, malicious media files could be distributed through common business communication channels.

Organizations should prioritize identifying systems with affected HEVC Video Extensions, verifying installed application versions, and deploying the appropriate October 2026 security updates.

“When a single media file can become a path to remote code execution, keeping video codecs updated is an important part of protecting business systems.”