CVE-2025-58186 is a vulnerability classified under CWE-400 (Uncontrolled Resource Consumption) found in the Go programming language's standard library, specifically in the net/http package. The root cause is that although HTTP headers have a default size limit of 1MB, the number of cookies parsed by the server is not limited. An attacker can exploit this by sending a large number of very small cookies (e.g., "a=;") in an HTTP request. Each cookie causes the server to allocate a separate struct in memory. Because there is no cap on the number of cookies, this can lead to excessive memory allocation, potentially exhausting server resources and causing denial of service (DoS). This vulnerability affects all Go versions from the initial release up to version 1.25.0. The vulnerability was reserved in August 2025 and published in October 2025. There are no known exploits in the wild at this time, and no patch links have been provided yet. The issue is significant because Go is widely used for building scalable web services, and the net/http package is a core component for handling HTTP requests. Without proper mitigation, servers using vulnerable versions of Go could be overwhelmed by crafted requests, impacting availability and potentially causing service outages.

For European organizations, the impact of CVE-2025-58186 can be substantial, particularly for those relying on Go-based web servers or microservices exposed to the internet. The uncontrolled resource consumption can lead to denial of service, causing service downtime and degraded performance. This can affect critical infrastructure, financial services, e-commerce platforms, and public sector services that depend on Go for backend operations. Memory exhaustion attacks can also increase operational costs due to resource over-provisioning or incident response efforts. Additionally, service unavailability can damage reputation and customer trust. Since the vulnerability does not require authentication or user interaction, it can be exploited remotely by any attacker capable of sending HTTP requests. The absence of a patch at the time of disclosure increases the urgency for organizations to implement interim mitigations. The impact is primarily on availability, with no direct confidentiality or integrity compromise reported.

To mitigate CVE-2025-58186, European organizations should take the following specific actions: 1) Monitor and limit the number of cookies accepted per HTTP request at the application or proxy level, implementing custom middleware or reverse proxy rules to reject requests with excessive cookies. 2) Employ Web Application Firewalls (WAFs) that can detect and block abnormal cookie patterns or unusually large numbers of cookies. 3) Upgrade to a patched version of the Go standard library once it is released by the Go project, as this will likely include limits on cookie parsing or improved resource management. 4) Implement rate limiting and request throttling to reduce the risk of resource exhaustion from repeated malicious requests. 5) Conduct thorough testing of Go-based services under high cookie load scenarios to identify potential memory issues. 6) Use container or process-level resource limits to prevent a single process from exhausting system memory. 7) Keep monitoring threat intelligence feeds for any emerging exploits or patches related to this vulnerability.