CVE-2026-77484 in SQL Server
Summary
by MITRE • 09/09/2026
Deserialization of untrusted data in SQL Server allows an authorized attacker to execute code over a network.
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Analysis
by VulDB Data Team • 09/09/2026
The vulnerability described involves the deserialization of untrusted data within Microsoft SQL Server, which presents a critical security risk by allowing authenticated attackers to achieve remote code execution through network-based interactions. This flaw stems from the server's handling of serialized objects that are not properly validated or sanitized before being processed. When an authorized user submits maliciously crafted input designed as a legitimate deserialization payload, the application inadvertently instantiates arbitrary classes and executes their methods during the unmarshalling process. This mechanism bypasses standard security controls because the attacker leverages existing authentication credentials to interact with the database engine, exploiting the trust relationship inherent in authenticated sessions rather than breaking through perimeter defenses or gaining unauthorized access from an external network position without prior login privileges.
From a technical perspective, this issue aligns closely with CWE-502, which denotes Deserialization of Untrusted Data. The core deficiency lies in the lack of integrity verification and type checking for incoming serialized streams. In many enterprise environments, SQL Server processes complex data structures that may include custom objects or extended properties. If these inputs are derived from user-controlled sources without rigorous schema validation or allow-listing of permissible types, an attacker can craft a payload containing gadget chains—sequences of object instantiations and method calls—that lead to the execution of arbitrary system commands. This is particularly dangerous because it transforms a routine data exchange operation into a vector for full system compromise, effectively turning the database server itself into an agent for further lateral movement within the network infrastructure.
The operational impact of this vulnerability is severe, as successful exploitation grants the attacker complete control over the underlying operating system running SQL Server. This level of access allows for the exfiltration of sensitive data stored in databases, modification or deletion of critical records, and the establishment of persistent backdoors. Furthermore, because the attack originates from a trusted authenticated source, it may evade detection by traditional network intrusion prevention systems that focus on external threats. The attacker can use the compromised database server as a pivot point to launch attacks against other internal assets, potentially leading to widespread organizational compromise. In high-availability or clustered environments, this could also disrupt service availability if the exploitation causes instability or crashes in the SQL Server process.
Mitigation strategies must address both immediate remediation and long-term architectural improvements. The primary defense is to apply the latest security patches provided by Microsoft that specifically rectify the deserialization logic flaws within affected versions of SQL Server. Organizations should ensure their patch management processes are agile enough to deploy these updates promptly, given the high severity of remote code execution vulnerabilities. Additionally, implementing strict input validation and output encoding practices for any custom applications interacting with the database can reduce the attack surface. It is also advisable to restrict network access to SQL Server instances using firewalls or virtual private networks, ensuring that only authorized hosts can communicate with the service. Enabling advanced auditing features helps in monitoring for anomalous deserialization activities, while adhering to the principle of least privilege ensures that even if exploitation occurs, the scope of potential damage is contained by limiting the permissions associated with database accounts used by applications and users.