CVE-2026-22611 is a vulnerability identified in the AWS SDK for .NET, specifically affecting versions from 4.0.0 up to but not including 4.0.3.3. The root cause is improper input validation (CWE-20) of the 'region' parameter used when making AWS API calls. This parameter determines the AWS region endpoint to which the SDK directs requests. If an attacker has access to the environment where the SDK is running, they can manipulate the region input to an invalid or malicious value, causing API calls to be routed to non-existent or potentially attacker-controlled hosts instead of legitimate AWS services. This can lead to scenarios where sensitive data intended for AWS services could be intercepted, redirected, or lost. The vulnerability does not require user interaction or prior authentication but does require the attacker to have some level of access to the environment (e.g., compromised host or insider threat). The CVSS v3.1 score is 3.7 (low), reflecting limited impact on confidentiality, no impact on integrity or availability, and a higher attack complexity. There are no known exploits in the wild, and AWS has addressed the issue in version 4.0.3.3 of the SDK. Organizations using affected versions should upgrade to the patched release to prevent potential exploitation.

For European organizations, the primary risk lies in the potential interception or misrouting of AWS API calls, which could expose sensitive data or disrupt cloud service interactions. Although the vulnerability requires attacker access to the environment, if exploited, it could facilitate data leakage or man-in-the-middle scenarios by redirecting requests to malicious endpoints. This risk is particularly relevant for enterprises heavily reliant on AWS cloud services via the .NET SDK, including sectors such as finance, healthcare, and government, where data confidentiality is critical. The impact on service availability and integrity is minimal, and the low CVSS score reflects this. However, the presence of this vulnerability could be leveraged as part of a broader attack chain, especially in environments with weak internal security controls. Prompt patching reduces the risk significantly. Given the widespread adoption of AWS in Europe, the vulnerability could affect a broad range of organizations, but exploitation complexity and prerequisite access limit its immediate threat level.

1. Upgrade all AWS SDK for .NET instances to version 4.0.3.3 or later to apply the official patch addressing this vulnerability. 2. Implement strict environment access controls to prevent unauthorized modification of SDK configuration parameters, including the region field. 3. Use runtime integrity monitoring to detect unexpected changes in SDK configuration or network routing behavior. 4. Employ network-level protections such as egress filtering and DNS monitoring to detect and block requests to unauthorized or suspicious endpoints. 5. Conduct regular audits of cloud SDK usage and configuration to ensure compliance with security best practices. 6. Incorporate application-level input validation and sanitization for any parameters influencing SDK behavior, even if the SDK itself performs validation. 7. Monitor logs for anomalous API call destinations or failed requests that could indicate exploitation attempts. 8. Educate developers and DevOps teams about the importance of secure SDK configuration and timely patching.