Microsoft has closed 57 security vulnerabilities in its December 2025 Patch Tuesday release, including three zero‑day issues affecting Windows, GitHub Copilot for JetBrains, and Windows PowerShell. One of these, a privilege escalation flaw in Windows, is already being actively exploited to gain SYSTEM‑level access, making timely patch deployment critical for both enterprise and individual users.
Zero‑Day Definition and Scope in Microsoft’s Security Ecosystem
Microsoft treats as zero‑day vulnerabilities not only bugs with confirmed in‑the‑wild exploitation, but also those that are publicly disclosed before a fix is available. Under this definition, the December 2025 patches address:
– One exploited Windows privilege escalation zero‑day
– One publicly disclosed command injection flaw in GitHub Copilot for JetBrains
– One publicly disclosed command injection vulnerability in Windows PowerShell
This approach reflects a broader industry trend: once technical details are public, the window for attackers to develop reliable exploits shrinks drastically, and the operational priority of patching increases even if exploitation has not yet been observed.
CVE‑2025‑62221: Windows Privilege Escalation to SYSTEM via Cloud Files Driver
The most critical issue in this cycle is CVE‑2025‑62221, rated 7.8 on the CVSS scale. It is a use‑after‑free vulnerability in the Windows Cloud Files Mini Filter Driver. An authenticated local attacker can exploit this bug to elevate privileges from a standard user context to SYSTEM, the highest level of privilege in Windows.
With SYSTEM access, an adversary can install backdoors, disable security controls, harvest credentials, and move laterally across the network. In typical intrusion kill chains, such privilege escalation vulnerabilities are used after initial compromise (for example, via phishing, macro abuse, or a browser exploit) to gain durable control over high‑value systems.
The flaw was discovered by the Microsoft Threat Intelligence Center (MSTIC) and the Microsoft Security Response Center (MSRC). Microsoft confirms that CVE‑2025‑62221 is being exploited in real‑world attacks but has deliberately withheld detailed technical information in its public advisory to slow down exploit development by additional threat actors. A related bug, CVE‑2025‑62454 (also CVSS 7.8), affecting the same driver and enabling similar privilege escalation, has likewise been fixed and should be treated as a high‑value target for future attacks.
GitHub Copilot and PowerShell: Command Injection and Developer Tooling Risk
CVE‑2025‑64671: Command Injection in GitHub Copilot for JetBrains IDEs
The vulnerability CVE‑2025‑64671 is a command injection issue in GitHub Copilot for JetBrains. It enables local code execution through prompt injection when the IDE interacts with untrusted files or MCP (Model Context Protocol) servers. Security researcher Ari Marzuk described the underlying class of issues in the report “IDEsaster: A Novel Vulnerability Class in AI IDEs”, highlighting how AI‑assisted development tools can be abused as an attack surface inside the developer workstation.
While there are no public reports of active exploitation, the vulnerability shows how AI coding assistants can become vectors for supply‑chain style attacks: a malicious repository, configuration file, or MCP endpoint could manipulate the AI assistant into generating or executing unsafe commands within the IDE.
CVE‑2025‑54100: Unsafe Invoke‑WebRequest Behavior in PowerShell
The second publicly disclosed zero‑day, CVE‑2025‑54100, is a command injection vulnerability in Windows PowerShell. When a user downloads a webpage using the Invoke‑WebRequest cmdlet, embedded scripts on that page may be executed due to improper neutralization of special elements in commands. This enables a remote, unauthenticated attacker to trigger local code execution if they can control or influence the retrieved content.
To mitigate the risk, Microsoft has changed the default behavior of PowerShell: running Invoke‑WebRequest now displays a warning and recommends explicitly specifying the -UseBasicParsing flag to reduce the likelihood of inadvertent script execution. For administrators and DevOps teams, this change should trigger a review of automation scripts, CI/CD pipelines, and infrastructure code where Invoke‑WebRequest is commonly used to fetch configuration files, installers, or deployment artifacts.
Microsoft Office Preview Pane RCE: High‑Impact Email Attack Surface
Beyond zero‑days, the December updates address 13 vulnerabilities in Microsoft Office. Two of them, CVE‑2025‑62554 and CVE‑2025‑62557, are rated critical (CVSS 8.4). These bugs (classified as type confusion and use‑after‑free) can lead to remote code execution (RCE) when Office processes specially crafted content.
A particularly concerning aspect is that the Office Preview Pane can act as the attack trigger. Under Microsoft’s worst‑case scenario, simply delivering a malicious email could be sufficient for exploitation: the victim does not need to open the attachment or click a link; rendering in Preview Pane may be enough. In environments heavily reliant on email and Office integration, this significantly amplifies the risk of targeted phishing and mass spam campaigns delivering exploit content.
2025 Vulnerability Trends and Patch Management Priorities
Over the course of 2025, Microsoft has fixed approximately 1,200 vulnerabilities across its product portfolio, marking the second consecutive year with more than a thousand issues addressed. This volume reflects the growing complexity of the Windows, Office, and cloud ecosystems, as well as the activity of security researchers and adversaries. As in previous years, many vulnerabilities fall into two dominant categories: privilege escalation and remote code execution, both essential building blocks in modern attack chains observed in incident reports and threat intelligence analyses.
Organizations should prioritize deployment of the December patches to:
– Windows endpoints and servers exposed to CVE‑2025‑62221 and CVE‑2025‑62454
– Developer environments using GitHub Copilot for JetBrains, especially those handling external or untrusted code
– PowerShell‑based automation and orchestration relying on Invoke‑WebRequest
– Mail and collaboration infrastructure deeply integrated with Microsoft Office and its Preview Pane
Effective risk reduction depends on centralized patch management, accurate software asset inventory, enforcement of the principle of least privilege, and regular configuration audits. By coupling timely deployment of security updates with strong baseline hardening and continuous monitoring, organizations make it substantially more difficult for attackers to chain zero‑day and n‑day vulnerabilities into successful, high‑impact compromises.
