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The Silent Threat Breaking Through SharePoint Defenses
In a chilling new development, cybersecurity experts at Bitdefender have confirmed that a critical vulnerability—CVE-2025-53770—is being actively and aggressively exploited in the wild. This severe remote code execution (RCE) flaw in on-premises Microsoft SharePoint Server systems has a CVSS score of 9.8, meaning it poses a near-total system compromise risk for unpatched systems.
This vulnerability allows unauthenticated attackers to execute arbitrary code remotely, using a deserialization flaw that bypasses previous patches. The flaw has already been exploited across a wide range of countries, including the United States, Germany, South Africa, and the Netherlands, triggering alerts from the U.S. Cybersecurity and Infrastructure Security Agency (CISA).
🚨 the Ongoing Exploitation Campaign
Bitdefender’s latest research confirms that CVE-2025-53770 is not just theoretical—it is being weaponized in real-time. The exploit, tied to a malicious campaign named “ToolShell”, takes advantage of a vulnerability in how SharePoint deserializes untrusted data.
Key Details:
Exploit Type: Remote Code Execution (Unauthenticated)
Affected Systems: Microsoft SharePoint Server 2016 (on-premises only)
Unaffected: SharePoint Online / Microsoft 365
Attack Scope: Global exploitation detected in over 10 countries
Attack Technique: Exfiltration of cryptographic MachineKeys, followed by the injection of malicious __VIEWSTATE payloads
The attackers are using malicious ASP.NET web shells to extract sensitive cryptographic keys (ValidationKey and DecryptionKey) from SharePoint’s MachineKey configuration. These keys allow them to forge legitimate-looking __VIEWSTATE payloads that grant full, persistent access to the compromised server.
Bitdefender has even shared a piece of the malicious code, which includes embedded C scripts capable of extracting these keys when a specially crafted page is loaded.
The threat is particularly urgent because attackers can re-enter the system at will, even after initial vulnerabilities are patched, if the stolen MachineKeys are not rotated.
Moreover, the exploitation window is shrinking fast—Bitdefender notes that it typically takes less than 24 hours between the release of Proof-of-Concept (PoC) code and automated exploitation attempts through global scans.
The implications are severe:
Persistence: Attackers maintain long-term access using stolen keys
Ransomware Risk: These RCEs are often the first step before deploying ransomware
Patch Evasion: This flaw bypasses two earlier CVEs (2025-49704, 2025-49706)
Organizations are advised to act immediately, apply security update KB5002760, and follow mitigation strategies from Microsoft and Bitdefender. In the meantime, rotating your MachineKeys is non-negotiable to eliminate the backdoor.
🔍 What Undercode Say:
Anatomy of an Advanced Exploit Chain
From an attacker’s perspective, the beauty of this exploit lies in its simplicity and power. Without any need for credentials, attackers can launch code directly onto the SharePoint server, gain cryptographic access, and deploy persistent malware.
Why This Exploit is Dangerous
No Authentication Required: This makes the vulnerability attractive to botnets and ransomware groups
Bypass Capabilities: Even previously patched servers are once again vulnerable
Automated Exploitation: Script kiddies to APTs can exploit it with minimal effort
Once MachineKeys are stolen, attackers have the cryptographic authority to fake session data indefinitely. This is equivalent to forging a secure login session—without needing a username or password. That’s why rotating MachineKeys post-intrusion is not optional; it’s vital.
Strategic Implications for Enterprises
This attack demonstrates how outdated or misconfigured on-premises environments are now prime targets for attackers. The fact that SharePoint Online is unaffected is telling: Microsoft’s cloud architecture isolates and mitigates threats faster than on-premises systems can.
In our analysis, this incident reflects a growing trend:
Ransomware-as-a-Service (RaaS) groups are shifting to supply chain and enterprise platforms
Proof-of-Concept (PoC) to Exploit Time is now under a day
Initial Access Brokers (IABs) are monetizing these RCEs by selling access to ransomware groups
✅ Fact Checker Results:
CVE-2025-53770 is officially recognized and listed by CISA 🟢
Bitdefender telemetry confirms active global exploitation ✅
Patch KB5002760 is the only official mitigation for SharePoint 2016 🔐
🔮 Prediction:
Given the trajectory of CVE-2025-53770, we can expect:
Increased ransomware attacks targeting unpatched SharePoint servers
Wave of exploits expanding beyond ToolShell into new malware variants
Major enterprise breaches traced back to overlooked on-prem deployments
Security professionals must not underestimate the speed and scale of these attacks. Migrating critical workloads to cloud-native environments and adopting Zero Trust Architecture (ZTA) will be essential strategies moving forward.
🛡️ As with all deserialization flaws, awareness and speed of response are the deciding factors between breach and safety. Don’t wait for the ransomware note—patch now, rotate keys, and hunt for IOCs!
References:
Reported By: www.bitdefender.com
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