CVE-2026-96251 in PowerShell
Summary
by MITRE • 10/15/2026
Reliance on untrusted inputs in a security decision in Microsoft PowerShell allows an unauthorized attacker to execute code over a network.
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Analysis
by VulDB Data Team • 10/15/2026
The vulnerability described involves a critical flaw within the execution logic of Microsoft PowerShell, specifically concerning how the environment handles and validates external data during security decisions. This issue stems from a reliance on untrusted inputs without adequate sanitization or validation before these inputs influence access control mechanisms or code execution paths. In practical terms, this means that an attacker who can inject malicious content into specific input vectors accessible to the PowerShell engine can manipulate its internal decision-making processes. The core technical flaw lies in the failure to properly distinguish between trusted system configurations and potentially hostile user-supplied data when determining whether certain actions should be permitted or blocked. This misconfiguration allows for a bypass of intended security restrictions, effectively granting an unauthorized actor elevated privileges or execution capabilities that were not originally granted by the system administrator.
From a technical perspective, this vulnerability aligns with CWE-20 Improper Input Validation and CWE-798 Use of Hard-coded Credentials if specific authentication tokens are involved in the decision process. The attacker exploits the lack of rigorous type checking and boundary validation on inputs that feed into security policies such as execution policy settings or script block logging configurations. By crafting a specially designed input, often through network-based protocols like WinRM or SMB which PowerShell frequently interacts with remotely, an adversary can trick the interpreter into executing arbitrary commands. This is particularly dangerous because PowerShell is deeply integrated into Windows operating systems and enterprise management frameworks, making it a high-value target for lateral movement and persistent access within corporate networks.
The operational impact of this vulnerability is severe, as it enables remote code execution without requiring user interaction or prior authentication in some configurations if the service exposing the interface is accessible over the network. An attacker can leverage this flaw to deploy malware, establish persistence mechanisms, exfiltrate sensitive data, or move laterally across a domain by exploiting trusted administrative tools. This capability significantly lowers the barrier for entry for threat actors, allowing them to compromise systems that were previously considered secure due to their reliance on PowerShell as an authorized management channel. The ability to execute code over a network amplifies the risk, turning what might be a local privilege escalation into a widespread remote exploitation scenario affecting multiple endpoints simultaneously if exploited via automated tools or worms.
This behavior is consistent with MITRE ATT&CK techniques such as T1059 Command and Scripting Interpreter, specifically PowerShell abuse, and potentially T1210 Exploitation of Remote Services depending on the specific vector used to deliver the malicious input. The vulnerability underscores the importance of implementing strict least-privilege principles for administrative accounts and ensuring that all external inputs are treated as hostile until proven otherwise. Mitigation strategies include applying vendor-provided security patches immediately upon release, configuring PowerShell Constrained Language Mode to restrict access to sensitive APIs and objects, and disabling unnecessary remote endpoints like WinRM if they are not required for business operations. Additionally, implementing application whitelisting solutions can prevent the execution of unauthorized scripts even if an attacker successfully exploits this input validation flaw. Regular auditing of script block logging and advanced threat protection policies should also be enforced to detect and alert on anomalous PowerShell activity that may indicate exploitation attempts in progress.