CVE-2026-22611 is a vulnerability classified under CWE-20 (Improper Input Validation) found in the AWS SDK for .NET, specifically affecting versions from 4.0.0 to before 4.0.3.3. The SDK facilitates integration with AWS services such as Amazon S3, DynamoDB, and Glacier by allowing developers to specify a region parameter that directs API calls to the appropriate AWS service endpoints. The vulnerability arises because the SDK does not sufficiently validate the region input field, enabling an attacker with access to the environment where the SDK is running to supply invalid or malicious region values. This improper input can cause the SDK to route API requests to non-existent or non-AWS hosts, potentially leading to misdirected network traffic or denial of service for legitimate AWS API calls. The flaw does not inherently allow data leakage, unauthorized data modification, or service disruption beyond routing issues. Exploitation does not require authentication or user interaction but does require the attacker to have access to the environment where the SDK is used, such as through compromised credentials or insider threat. AWS addressed this vulnerability by releasing version 4.0.3.3 of the SDK, which implements proper validation of the region parameter to ensure only valid AWS regions are accepted, preventing the routing of API calls to unintended hosts. No public exploits or active exploitation have been reported to date.

For European organizations, the impact of CVE-2026-22611 is primarily operational rather than directly compromising security. Misrouting AWS API calls could lead to application errors, failed service interactions, or potential denial of service conditions if API requests do not reach legitimate AWS endpoints. This could disrupt business-critical cloud services relying on AWS SDK for .NET, affecting availability and reliability of applications. However, since the vulnerability does not expose sensitive data or allow unauthorized actions, the confidentiality and integrity impact is minimal. Organizations with strict compliance requirements or those operating critical infrastructure may experience indirect impacts due to service interruptions. The risk is higher in environments where attackers can gain environment access, such as through compromised developer machines, CI/CD pipelines, or insider threats. European companies heavily dependent on AWS cloud services and using the affected SDK versions should prioritize patching to maintain operational stability and prevent potential exploitation scenarios that could degrade service quality.

European organizations should immediately upgrade all instances of AWS SDK for .NET to version 4.0.3.3 or later to ensure the region input validation flaw is remediated. Additionally, organizations should audit their environments to restrict access to systems running the SDK, minimizing the risk of attackers manipulating environment variables or configuration files. Implement strict access controls and monitoring on developer workstations, build servers, and deployment pipelines to detect unauthorized changes to SDK configuration parameters. Employ network segmentation and egress filtering to prevent API calls from being routed to unauthorized external hosts. Incorporate runtime application self-protection (RASP) or API gateway validation to detect and block anomalous API requests with invalid region parameters. Regularly review and update software dependencies to avoid running vulnerable SDK versions. Finally, conduct security awareness training for developers and operations teams about the risks of environment manipulation and the importance of timely patching.