Critical SharePoint Vulnerability Exploits Highlight Urgent Security Measures for On-Premises Deployments

Microsoft’s security response apparatus was put to the test yet again this July, following the public disclosure and exploitation of multiple high-severity vulnerabilities impacting on-premises SharePoint Server deployments across a spectrum of enterprise, government, and regulated industries. With remote code execution attacks erupting “in the wild”—targeting business-critical collaborative portals and intranets—Microsoft’s urgent security advisory, subsequent patch rollouts, and rapid engagement with federal cybersecurity authorities signal both the evolving threat environment and the shifting calculus of IT risk management. For IT professionals, enterprise architects, security practitioners, and decision-makers relying on SharePoint’s document-management functionality, the lessons of this incident are likely to resonate long after the current headlines fade.

The Anatomy of the Latest SharePoint Attacks​

This summer’s incident centers on CVE-2025-53770 and CVE-2025-53771, classed as critical remote code execution (RCE) vulnerabilities within locally hosted Microsoft SharePoint Server. According to Microsoft, these attacks are actively being used against business and public sector targets, leveraging a dangerous form of software bug known as “deserialization of untrusted data.” In stark contrast to vulnerabilities requiring either high levels of privilege or some form of user interaction, this flaw allows threat actors to craft and send specially designed payloads directly to SharePoint’s exposed components. The resulting exploitation could grant attackers the ability to execute arbitrary commands on the underlying Windows server—potentially resulting in full system takeover, data theft, ransomware implantation, or the launch pad for further lateral movement within a victim’s network.
In its advisory, Microsoft is clear: these issues afflict only on-premise deployments of SharePoint (SharePoint Server 2016, 2019, Subscription Edition), not the cloud-based SharePoint Online component of Microsoft 365—a crucial distinction as the steady migration toward cloud software continues. Customers using cloud-hosted SharePoint are not impacted, reinforcing the narrative that robust cloud architectures can, in some instances, insulate organizations from vulnerabilities endemic to legacy, self-managed platforms.

Technical Dissection: Why Deserialization Bugs are so Perilous​

Deserialization vulnerabilities, while not new in the world of enterprise software, occupy a feared spot in the hierarchy of software flaws. Deserialization is the process of reconstructing “serialized” data—often formatted as binary streams or object graphs—back into programmatic objects for use in application logic. If this occurs without strict verification of the data’s source and integrity, and if the code paths that process the reconstructed objects are not fortified, attackers can essentially “smuggle” hostile instructions or dangerous object types into the application runtime.
Historically, such flaws have enabled devastating hacks—most notably the Apache Struts bug leveraged in the Equifax breach. In the case of CVE-2025-53770, Microsoft’s patch notes and independent security researchers confirm the flaw arises from SharePoint’s failure to perform adequate validation during deserialization, thus exposing code execution pathways to remote, unauthenticated adversaries. The technical risk is amplified by the absence of any need for privileged access: attackers merely require network connectivity to the server.

Timeline and Scope of Attacks​

Actionable threat intelligence poured in through late June and early July, as various honeypots and public sector incident response teams began to detect exploitation attempts targeting exposed SharePoint endpoints. As reports surfaced, Microsoft confirmed “active attacks” and issued out-of-band security guidance mandating the immediate application of security updates.
The U.S. Cybersecurity and Infrastructure Security Agency (CISA) responded in parallel, adding CVE-2025-53770 to its Known Exploited Vulnerabilities (KEV) catalog. The agency’s directive stipulated that federal civilian agencies must remedy the flaw by July 21, 2025, at latest—underscoring the criticality as judged by national cybersecurity standards.

Who Is at Risk?​

SharePoint’s reach within modern organizations is extensive. As a linchpin of digital transformation—powering document workflows, business automation, portal services, and regulated data management across sectors—SharePoint Server installations regularly straddle both critical business operations and sensitive data repositories. Beyond large, Fortune 500-class firms, SharePoint is ubiquitous in mid-market enterprises, educational institutions, and government. Its tight integration with identity services like Active Directory, custom plugins, and line-of-business automation further amplify the impact of compromise.
While the scope of attack is limited to on-premises SharePoint, the affected population is global. Public web scans and telemetry from security vendors indicate tens of thousands of exposed SharePoint deployments across North America, Europe, the Middle East, and beyond. The situation is even more acute for organizations running hybrid environments, where legacy SharePoint servers may persist behind firewalls, used for integration scenarios not (yet) migrated to Microsoft 365.

Exploitation Chain: How Do These Attacks Unfold?​

The paradigmatic attack chain for this vulnerability is both direct and chillingly efficient:

• The attacker scans for accessible SharePoint endpoints (often using automated tools or Shodan searches).
• Crafted serialized objects containing a “gadget chain” are transmitted to SharePoint’s REST API or related upload endpoint.
• Inadequate input validation during deserialization allows the malicious object to trigger code execution in the application pool context.
• With successful exploitation, the threat actor gains the ability to run commands; this may include installing malware, creating new user accounts, siphoning data, or pivoting laterally within the corporate network.

Notably, these attacks are typically unauthenticated—no user interaction is needed, nor does the attacker require valid sign-ins or administrator privilege.

Patch and Mitigation: Microsoft’s Guidance​

Microsoft’s patching guidance, circulated widely in July’s security update, is unequivocal: organizations running SharePoint Server Subscription Edition or SharePoint 2019 must apply the released updates immediately to avoid a dramatically heightened risk of compromise. The company further instructs administrators to rotate SharePoint server ASP.NET machine keys and restart the IIS web server component following patch application—a step designed to ensure integrity if any authentication artifacts were harvested during prior exploitation attempts.
For those unable to deploy Active Malware Scanning Interface (AMSI), Microsoft insists that machine key rotation is mandatory even after patching. The urgency of these measures reflects both the technical nature of the flaw and the confirmed exploitation campaigns.

Mitigation Steps—A Checklist​

• Apply the latest cumulative security updates for your SharePoint Server edition.
• Rotate ASP.NET machine keys via the documented key management process.
• Restart IIS on all SharePoint servers to enforce the key change and ensure no residual trust in potentially compromised cryptographic assets.
• Restrict network exposure: Where feasible, ensure SharePoint admin interfaces are only accessible via VPN, jump stations, or restricted subnets.
• Audit server logs and monitor for new privileged users, lateral movement indicators, or signs of process injection stemming from SharePoint application context.
• Review custom plugins and workflows for insecure serialization behavior; patching the Microsoft-supplied code does not guarantee safety from vulnerabilities introduced by third-party add-ons.

The Broader Context: SharePoint in the Modern Threat Landscape​

This is not the first, nor will it be the last, time SharePoint figures into a large-scale enterprise security crisis. Time and again, collaboration platforms with extensible plugin architectures and deep integration into enterprise IT stacks have fallen victim to flaws deriving from both legacy design and the rapid push for new features. SharePoint—by virtue of its business centrality and the technical latitude given to administrators, developers, and integrators—remains a perennial favorite for both red and blue teams.
Persistent features of SharePoint exploitation trends include:

• Attackers leveraging internet-facing SharePoint endpoints for initial access, bypassing VPN or single sign-on entirely.
• Rapid emergence of proof-of-concept (PoC) code after Patch Tuesday updates, often within 24 to 72 hours, as cybercriminals reverse-engineer diffed binary patches.
• Real-world ransomware campaigns, data theft, and espionage often tracked back to unpatched or misconfigured SharePoint instances.

Security researchers from respected industry groups (as well as CISA) have repeatedly spotlighted deserialization flaws as a recurring issue that demands defense-in-depth, not simply patching after-the-fact.

Critical Analysis: Microsoft’s Strengths and Shortcomings​

Strengths

• Rapid Communication: Microsoft’s transparency and speed in acknowledging actively exploited zero-day flaws is recognized as a major strength. Unlike in previous decades, today’s Microsoft is proactive in both technical detail and urgency of guidance, empowering IT and SecOps teams to act decisively.
• Patch Breadth and Timeliness: The company’s capacity to simultaneously release updates for legacy and current SharePoint versions—and to coordinate guidance with national security authorities—reflects ongoing maturity in software lifecycle and coordinated vulnerability disclosure.
• Community Vigilance: The rapid response from security vendors to update signatures, raise alerts, and conduct post-patch threat hunting illustrates a robust ecosystem supporting Microsoft’s efforts.

Risks and Exposed Weaknesses

• Legacy and Custom Deployments: Many enterprises continue to run unsupported or unpatched versions of SharePoint for compatibility, regulatory, or budgetary reasons. These “shadow IT” deployments, often outside formal asset management, remain exposed to attack unless isolated or decommissioned.
• Complexities of Patching: In large organizations with intricate SharePoint customizations or unique third-party integrations, the fear of breaking critical workflows often leads to update delays. The patch lifecycle for SharePoint can span weeks or even months—opening a dangerous window for attackers.
• Lack of Deserialization Awareness: Not all IT admins are well-versed in the dangers of insecure deserialization, leading to undue complacency or insufficient urgency in patch cycles.
• Potential for Chained Attacks: SharePoint’s integration with authentication services (Active Directory, Entra) means that a single breach could escalate into domain-wide compromise, risk to identity fabric, and potential trust erosion for users and regulators.
• Zero-Day Arms Race: With public exploit code and scanning routines now appearing rapidly after vulnerability disclosures, even short-term delays in patch adoption increase real-world risk grounds.

From Tactical Response to Strategic Resilience​

The lessons distilled from CVE-2025-53770 and its exploitation traverse well beyond SharePoint and Microsoft to the wider enterprise software landscape:

• Expect persistent risk from legacy serialization and integration features.
• Operationalize a true defense-in-depth approach: patch promptly, but also segment networks, restrict privileges, and harden management interfaces.
• Proactively test updates—using phased deployment, pilot groups, and regression checks—to minimize workflow disruptions while not sacrificing security for stability.
• Invest in continuous education and tabletop exercises for SecOps and IT teams on recognizing serialization patterns, incident response, and active exploit monitoring.
• Demand secure-by-default design from vendors, pushing for architectural hardening in future releases.

Conclusion: No Silver Bullet, but Clear Mandates​

The most recent SharePoint vulnerability wave, culminating in the rapid exploitation of deserialization flaws and the mobilization of both Microsoft and federal agencies, encapsulates the modern cyber risk paradox. On one hand, patch management and technical hygiene have never been better understood; on the other, operational complexity and legacy technical debt stubbornly persist.
This cycle will repeat—on SharePoint, Exchange, ERP, and collaboration platforms yet to come. What can change, however, is the speed and discipline with which organizations translate technical alerts into decisive action; the rigor with which they inventory, segment, and harden their most sensitive collaboration systems; and the urgency they impart upon software vendors to ship platforms that are, at their core, resistant to entire categories of logic flaws.
For organizations still running on-premises SharePoint, this event is more than a headline. It is a mandate to audit, patch, and prepare—not just for the exploit at hand, but for the wider digital transformation toward secure collaboration in an adversarial world.

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Source: Eastern Mirror Tech giant Microsoft issues urgent security patch after ‘active attacks’ on document-sharing software