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Is your legacy Windows server vulnerable to the critical CredSSP exploit?
Critical Security Update: 0patch Release for CredSSP Vulnerability
Ahead of the January 2026 Patch Tuesday, ACROS Security released a vital micropatch addressing CVE-2025-47987. This update targets an Elevation of Privilege (EoP) flaw within the Credential Security Support Provider Protocol (CredSSP). While Microsoft addressed this issue for supported systems in July 2025, this new micropatch provides essential protection for legacy environments that no longer receive official security maintenance.
Understanding the CredSSP Protocol
The Credential Security Support Provider Protocol (CredSSP) serves as a security agent for applications. It delegates encrypted user credentials from a client machine to a target server during remote authentication requests. This delegation process is critical for remote desktop services and similar administrative tools. When this protocol fails, the integrity of remote sessions is compromised.
Technical Analysis of CVE-2025-47987
This specific vulnerability functions as a heap-based buffer overflow within the Windows Cred SSProvider protocol. It poses a significant risk to system integrity:
- The Mechanism: The flaw exists due to insecure integer addition operations within the protocol code.
- The Impact: An authorized attacker can exploit this overflow to escalate their privileges locally on the target machine.
- Severity: Classified as High, this vulnerability carries a CVSS score of 7.8.
Microsoft originally disclosed and patched this flaw during the July 2025 update cycle. Their solution involved replacing the faulty addition operation with a safe function designed to detect overflows and halt the processing of malicious user-provided data.
The 0patch Solution for Legacy Systems
On January 6, 2026, ACROS Security announced the availability of a third-party micropatch for CVE-2025-47987. This development is crucial for organizations running infrastructure that falls outside Microsoft’s current support lifecycle.
Who needs this micropatch?
This security fix is mandatory for administrators managing systems without an Extended Security Update (ESU) license, including:
- Windows 7
- Windows Server 2008
- Older, unsupported iterations of Windows 10 and 11
By applying this micropatch, legacy systems gain the same overflow detection capabilities introduced in the official Microsoft patch, effectively neutralizing the privilege escalation vector.