CVE-2025-11915 is a vulnerability classified under CWE-444, indicating an inconsistent interpretation of HTTP requests, commonly known as HTTP request/response smuggling. This flaw specifically affects Google Cloud's Vertex AI Partner Models for MaaS (Model as a Service). The root cause is a connection desynchronization issue between the HTTP proxy layer and the backend model service. In such scenarios, the proxy and backend server interpret the boundaries of HTTP requests or responses differently, allowing an attacker to smuggle crafted HTTP requests through the proxy. This can lead to various attack vectors such as request hijacking, cache poisoning, or bypassing security controls. The vulnerability is remotely exploitable without authentication or user interaction, increasing its risk profile. However, the impact is limited to partial confidentiality and availability degradation, as indicated by the CVSS vector (VC:L, VI:N, VA:L). Google has proactively rolled out fixes for all proxies in front of the affected models by September 28, 2025, mitigating the risk at the infrastructure level. No user-side patches or configuration changes are required, and no known exploits have been reported in the wild. The vulnerability highlights the challenges in complex cloud service architectures where multiple HTTP handling components must maintain strict protocol synchronization to prevent such attacks.

For European organizations leveraging Google Cloud Vertex AI Partner Models, this vulnerability could allow attackers to manipulate HTTP traffic between the proxy and backend AI models, potentially leading to unauthorized data exposure or service disruption. While the confidentiality impact is limited, sensitive AI model inputs or outputs could be partially exposed or altered, affecting data integrity and trustworthiness of AI-driven decisions. Availability impacts could manifest as degraded service or denial of AI model responses, disrupting business processes dependent on these AI services. Given the cloud-managed nature and Google's prompt patch deployment, the window of exposure is narrow. However, organizations with legacy or custom proxy configurations might still be vulnerable if not aligned with Google's updates. The threat is particularly relevant for sectors relying heavily on AI services for critical operations, such as finance, healthcare, and manufacturing. Additionally, any exploitation attempts could complicate incident response due to the complex proxy-backend interactions. Overall, the impact is moderate but warrants attention to ensure continuous AI service reliability and data protection.

Organizations should verify that their Google Cloud Vertex AI Partner Models are operating behind updated proxies as per Google's September 2025 patch rollout. Although Google states no user action is needed, it is prudent to audit network configurations and proxy versions to confirm compliance. Monitoring HTTP traffic for anomalies indicative of request smuggling, such as unexpected request boundaries or duplicated headers, can provide early detection of exploitation attempts. Employing Web Application Firewalls (WAFs) with specific rules to detect and block smuggling patterns can add an additional defense layer. For organizations using custom or third-party proxies in front of Vertex AI, ensure these components are updated to handle HTTP parsing consistently. Regularly review cloud provider security advisories and integrate automated patch management for cloud services. Finally, conduct security awareness training for DevOps and security teams on HTTP protocol nuances to prevent misconfigurations that could facilitate such vulnerabilities.