June 2025 Windows Patch Tuesday: Zero-Days, Legacy Protocols, and Critical Security Fixes

June 2025's Patch Tuesday brought a sense of urgency back to the Windows security community, as Microsoft addressed a suite of 67 new vulnerabilities—among them, two zero-day exploits and multiple high-profile threats targeting legacy protocols and modern productivity tools. As enterprises and individuals increasingly depend on the stability of the Windows ecosystem, the stakes for prompt patch management and informed system administration have seldom been higher. This feature unpacks the technical details, analyzes the risks, and guides administrators and users in navigating the implications of this significant security update.

Critical Vulnerabilities: The Big Picture​

Microsoft's June 2025 cumulative update cycle tackles 67 newly identified vulnerabilities spread across core Windows components, server roles, and productivity applications. Notably, eight of these issues are classified as "critical"—those that enable remote code execution (RCE), potentially allowing attackers to run arbitrary code on vulnerable systems without significant user interaction. Two zero-day vulnerabilities stood out due to their potential for widespread exploitation: one in the WebDAV protocol stack (CVE-2025-33053) and another in the SMB client (CVE-2025-33073).
According to Microsoft's public advisory and corroborated by the Cybersecurity and Infrastructure Security Agency's (CISA) Known Exploited Vulnerabilities (KEV) catalogue, at least one of these flaws had already been used in active attacks. This aligns with recent trends, as threat actors increasingly seize upon unpatched zero-days within hours of disclosure. Security professionals and IT departments are, therefore, on high alert whenever 'Patch Tuesday' rolls around, but the variety and potential impact of this month's issues make the June 2025 cycle particularly noteworthy.

Zero-Day in WebDAV: Legacy Technology, Modern Risk​

The spotlight this month falls on CVE-2025-33053, the first publicly acknowledged zero-day in Microsoft's implementation of WebDAV in seven years. WebDAV, or Web Distributed Authoring and Versioning, is a protocol designed in the late 1990s to enable collaborative web content editing and file sharing over HTTP. Though largely regarded as legacy technology—its heyday was in early versions of Microsoft Exchange Server—WebDAV continues to persist as a supported feature in all current Windows releases, including Server 2025 and Windows 11 24H2.

Technical Overview​

• Vulnerability: CVE-2025-33053 (WebDAV RCE, Zero-Day)
• Attack Complexity: Low
• User Interaction Required: Yes — exploitation is triggered when a user clicks a malicious link.
• Scope: All supported Windows versions, including newest Server and Windows 11 releases.

Despite its deprecation (Microsoft announced in November 2023 that the associated WebClient service would no longer start by default), the persistence of WebDAV within the Windows codebase presents a stubborn attack surface. On new machines, such as those running Windows Server 2025, administrators can still add the “WebDAV Redirector” feature, which in turn reactivates the WebClient service and revives the legacy protocol stack.
Publicly, Microsoft attributes the discovery and responsible disclosure of the vulnerability to Check Point Research (CPR), who have associated it with Stealth Falcon, an advanced persistent threat (APT) group with a documented history of targeting government organizations in the Middle East and beyond. This attribution is supported by multiple security vendors, though specific technique details remain closely held by researchers due to the ongoing threat of in-the-wild exploitation.

Legacy Meets Modern Deployment​

One of the paradoxes of modern system administration is the continued relevance of old protocols like WebDAV. Though rarely required for day-to-day operation, these features remain in the code for backward compatibility or specialized enterprise needs. Microsoft's decision to release patches for every supported Windows OS—regardless of default service status—underscores their risk calculus: code that isn’t actively enabled still poses a threat if misconfigured, re-enabled by administrators, or targeted in complex chained exploits.

Analysis and Risks​

• Strengths: Microsoft's broad scope of patch deployment indicates a proactive stance; disabling the WebClient service by default further reduces exposure.
• Risks: The necessity for user interaction (clicking a malicious link) lowers, but does not eliminate, mass-exploitation potential—especially given ongoing phishing campaigns targeting enterprise environments.
• Unverified Claims: While public reports link the exploit to a specific APT, readers should treat such attribution with caution until more technical details emerge from incident analyses and forensic reporting.

In summary, organizations still relying on WebDAV or with legacy server roles enabled must prioritize patching, implement strict network segmentation, and consider disabling rarely used components unless absolutely required.

SMB Client Zero-Day: Privilege Escalation in Focus​

CVE-2025-33073, the second zero-day in this cycle, exploits the ubiquitous SMB (Server Message Block) client to escalate privileges to SYSTEM—a level of authority that gives attackers control over the entire affected system. According to Microsoft's advisories and industry analysis, exploitation occurs when a user connects to a malicious SMB server. The details provided by Microsoft introduce some ambiguity: it's unclear whether authentication is required for successful exploitation, a point of confusion echoed by Adam Barnett of Rapid7. Such ambiguity is not unfamiliar in initial patch advisories and is often due to a lack of complete incident data at the time of release.

Technical Overview​

• Vulnerability: CVE-2025-33073 (SMB Client EoP, Zero-Day)
• Attack Vector: Network (via malicious SMB server)
• Privileges Gained: SYSTEM
• Disclosure: Publicly disclosed before the patch's release.

The breadth of systems potentially at risk from SMB-related attacks cannot be overstated: SMB is integral not only to Windows file sharing but also to printer access, network browsing, and even various enterprise security solutions. Past SMB vulnerabilities (such as those exploited by WannaCry in 2017) have led to rapid, worm-like propagation on poorly segmented networks, making even privilege escalation issues without direct remote code execution a high-priority concern.

Analysis and User Concerns​

• Strengths: Microsoft's quick patch rollout minimizes the "window of opportunity" for opportunistic attackers, and vendor clarifications can be expected in future documentation updates.
• Risks: Ambiguity over the requirements for exploitation warrants a "better safe than sorry" approach: all endpoints with SMB client activity should be patched immediately, and organizations should monitor for anomalous outbound SMB connections—a classic sign of attempted lateral movement inside compromised networks.

Given the importance of SMB for everyday operations, disabling the service is rarely feasible. Instead, layered defense (network firewalls, endpoint detection, and robust user education) remains crucial.

Windows KDC Proxy Vulnerability: Targeting Domain Boundaries​

Out of the eight critical RCE flaws, CVE-2025-33071 stands out for its impact on domain controller infrastructure—a preferred target for attackers seeking to compromise entire enterprise domains. The KDC Proxy service, used for relaying Kerberos authentication requests between untrusted and trusted environments, is rarely enabled by default but is common in complex, highly segmented, or cloud-connected networks.

Technical Overview​

• Vulnerability: CVE-2025-33071 (KDC Proxy RCE, Critical)
• Attack Prerequisite: Target must act as a Kerberos Key Distribution Center Proxy Protocol server.
• Exploitation: Unauthenticated, but requires winning a "race condition," limiting ease of attack.
• Exposure: Considered higher due to the protocol role in routing authentication requests across boundaries.

Microsoft's own characterization that exploitation is "more likely" should prompt immediate attention from administrators overseeing exposed or internet-facing KDC proxies. As Barnett of Rapid7 advises, "Patching this vulnerability should be top of mind for affected defenders this month." The strategic location of these proxy servers means a successful intrusion could grant attackers a pivot point directly into domain credential flows—a long-standing cybersecurity nightmare.

Best Practices and Mitigation Strategies​

• Prompt patch deployment for all servers with the KDC Proxy role.
• Restrict external access whenever possible, using firewall rules and VPNs.
• Monitor for race-condition exploits, which may appear as intermittent authentication failures or unusual proxy server logs.
• Conduct a thorough role inventory—many organizations are unaware they are running services with such privileges.

Targeting Productivity: Office Preview Pane Vulnerabilities​

No Patch Tuesday would be complete without updates to Microsoft Office, but this cycle brought attention to three closely related RCE vulnerabilities (CVE-2025-47162, CVE-2025-47164, CVE-2025-47167) all leveraging the notoriously dangerous Office Preview Pane. Flaws here are particularly worrisome: simply previewing an attachment in Outlook or Windows Explorer—without opening it—can trigger malicious code execution.

Key Details​

• Vulnerabilities: CVE-2025-47162, CVE-2025-47164, CVE-2025-47167
• Vector: Office Preview Pane
• Impact: Remote Code Execution
• Affected Software: Most supported versions of Office, though patches are not yet available for Microsoft 365 Apps for Enterprise (sometimes labeled "Microsoft 365 for Office").

Security researchers discovered these issues as part of a focused assessment, and exploitation is considered "more likely," according to Microsoft. Historically, Office Preview Pane bugs have been leveraged in targeted spear-phishing campaigns, particularly those aimed at finance and executive roles where high-impact access can be gained with minimal user interaction.

What Should Admins Do?​

• Deploy patches as soon as available. For Microsoft 365 Apps for Enterprise, watch advisories closely and consider temporary workarounds (such as Group Policy restrictions on preview features) until official fixes are released.
• Educate users about the risks of previewing unfamiliar attachments, no matter how benign they may appear.
• Leverage endpoint security tools to analyze and quarantine suspicious Office documents before user access.

Ongoing Product Lifecycle Management​

While the June 2025 update does not introduce major changes to product support timelines, it serves as a reminder that planning for end-of-life milestones must remain part of any organization's security posture. The next significant lifecycle events—such as the sunset of SQL Server 2012 Extended Security Updates and the transition for Visual Studio 2022 17.8 LTSC—are slated for July 2025. Enterprises are encouraged to map upgrade and migration pathways well in advance to avoid a surge of unpatchable vulnerabilities.

Critical Takeaways: Strengths and Gaps in Microsoft’s Security Response​

What Microsoft Did Right​

• Comprehensive, preemptive patches: By issuing fixes for all versions, including those where legacy components are disabled by default, Microsoft demonstrates awareness of both configuration drift and advanced attack techniques that re-enable deprecated services.
• Improved transparency: The documentation references multiple independent sources and, where possible, provides acknowledgements for vulnerability discovery.
• Infrastructure-wide coverage: Updates extend beyond desktop OSs to server roles, protocol stacks, and widely deployed Office productivity tools.
• Speed of response: Quick inclusion of active zero-days, even those with public exploits, helps minimize "time-to-patch" exposure windows for organizations.

Where Gaps Remain​

• Advisory Clarity: For the SMB client zero-day, key elements remain ambiguous (authentication requirements, exploit chain details), which limits risk assessment and hinders incident response efforts.
• Patch Gaps for Cloud-First Software: The delay in Office 365 patching for critical vulnerabilities is a reminder that cloud-connected software sometimes follows separate remediation timelines. Enterprises must stay diligent across both on-premises and SaaS footprints.
• Legacy Code Exposure: The continued presence of WebDAV and similar protocols—despite being "deprecated"—illustrates the difficulty vendors face in fully excising obsolete features.

The Bigger Picture: Patch Management and Security Hygiene​

June 2025's Patch Tuesday is more than a single event—it's a spotlight on the challenge facing every organization using Microsoft technologies: how to keep sprawling, interconnected systems both functional and secure. As the stories of WebDAV and SMB illustrate, the threat landscape includes not only new vulnerabilities in novel code, but also lingering attack surfaces from decades-old features.

Security Recommendations for System Administrators​

• Patch Promptly: Enterprises should aim to deploy security updates within days, not weeks, especially for vulnerabilities with known public exploits.
• Scan for Legacy Protocols: Regularly audit systems for unused or deprecated components (WebDAV, SMB v1, legacy mail protocols) and disable or remove them whenever possible.
• Network Segmentation: Isolate critical roles (such as KDC Proxy servers) from general-purpose networks; apply firewalls and microsegmentation to limit attacker movement.
• Monitor for Exploitation: Use endpoint detection and response (EDR) solutions to hunt for indicators of compromise associated with the latest CVEs; monitor unusual SMB and WebDAV traffic.
• Educate End Users: Continual training to recognize phishing, suspicious links, and the dangers of ambiguous file attachments remains one of the most cost-effective defenses.
• Stay Informed: Subscribe to official advisories from Microsoft, CISA, and trusted security vendors for the latest remediation guidance, especially when details are ambiguous or newly clarified.

Concluding Analysis: Security Is an Ongoing Process​

Microsoft's multi-layered approach in June 2025 pushes back against both headline-grabbing zero-days and quieter, yet no less dangerous, protocol flaws. Yet even as vendors patch and document, the responsibility ultimately rests with IT leaders to keep their environments resilient. The persistence of legacy protocols like WebDAV, the omnipresence of SMB, and the everyday lure of Office document exploits underscore one essential truth: security is a journey, not a destination.
Whether your organization is deploying Windows Server 2025 in data centers or relying on Microsoft 365 in the cloud, the formula for success remains constant: rapid patch deployment, reduction of attack surfaces, deep monitoring, and user education. As zero-days move from the realm of obscure exploits to in-the-wild attacks with increasing speed, every patch cycle is an opportunity to harden defenses—and every unpatched system is a door left temptingly ajar for threat actors.
By embracing both technical excellence and a culture of vigilance, enterprises can transform Patch Tuesday from a moment of anxiety into a cornerstone of robust, proactive cybersecurity.

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Source: SecurityBrief Australia Microsoft tackles WebDAV zero-day in June 2025 patch update