CVE-2025-58186 is a vulnerability classified under CWE-400 (Uncontrolled Resource Consumption) found in the Go standard library's net/http package. The root cause is that while 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 data structure, leading to excessive memory allocation. This can cause the server to consume large amounts of memory, potentially leading to degraded performance, denial of service, or crashes. The vulnerability affects all Go versions from 0 up to and including 1.25.0. The CVSS v3.1 base score is 5.3 (medium severity), with an attack vector of network, low attack complexity, no privileges required, no user interaction, and impact limited to availability (no confidentiality or integrity impact). There are no known exploits in the wild at the time of publication. The vulnerability is particularly relevant for HTTP servers implemented using the Go net/http package, which is widely used in modern web services and cloud-native applications. Since the flaw is in the standard library, any Go application that does not implement additional cookie limits is potentially vulnerable. The lack of a patch link suggests that a fix may not yet be released or publicly available, emphasizing the need for interim mitigations.

For European organizations, this vulnerability poses a risk primarily to the availability of web services built with the Go net/http package. Exploitation can lead to denial-of-service conditions by exhausting server memory resources, causing service slowdowns or crashes. This can disrupt business operations, customer access, and critical online services. Organizations in sectors such as finance, healthcare, government, and technology that rely on Go-based HTTP servers are particularly vulnerable. The impact is heightened in environments with high traffic volumes or where attackers can easily send crafted HTTP requests. Additionally, cloud service providers and SaaS companies using Go may face cascading effects if their infrastructure is affected. While confidentiality and integrity are not directly impacted, the availability degradation can lead to reputational damage and financial losses. The medium severity rating reflects the moderate difficulty of exploitation but significant potential disruption. European entities with stringent uptime requirements and regulatory obligations around service availability must address this vulnerability promptly.

To mitigate CVE-2025-58186, European organizations should implement several practical measures beyond generic patching advice. First, monitor and limit the number of cookies accepted per HTTP request at the application or reverse proxy level (e.g., using NGINX or Envoy filters) to prevent excessive cookie counts. Implement rate limiting and request size restrictions to reduce the risk of resource exhaustion. Employ Web Application Firewalls (WAFs) configured to detect and block abnormal cookie patterns or unusually high cookie counts. Until an official patch is released, consider upgrading to the latest Go version if it includes a fix or apply vendor-provided patches. Conduct thorough testing of Go-based services to identify memory usage anomalies under high cookie loads. Additionally, implement robust monitoring and alerting for memory consumption spikes and service performance degradation. Educate developers to validate and sanitize HTTP headers and cookies. Finally, consider deploying container or process-level resource limits to contain the impact of potential attacks.