Hugo's security.http.urls allowlist is the only control on outbound fetches made by resources.GetRemote, and it inspects the URL text alone. CheckAllowedHTTPURL in config/security/securityConfig.go applies the configured pattern list and then re-checks a canonicalised form of an integer, hex or octal IPv4 host, but it never resolves the hostname and never inspects the address the HTTP client actually connects to. The client constructed in resources/resource_factories/create/create.go installs no dial-time hook, so no check occurs at connection time either. A hostname that resolves to a loopback, private or cloud-metadata address therefore satisfies the policy, and the response body is embedded in the generated site. An attacker who can supply a URL through content, for example a front-matter field or a CMS field, can make the build fetch an internal endpoint and publish the response in the static output, so the build artifact itself carries the data out.

CVE-2026-10582 describes a Server-Side Request Forgery (SSRF) vulnerability in the Hugo static site generator. Hugo's security.http.urls allowlist, which governs outbound HTTP fetches via resources.GetRemote, only inspects URL text and does not resolve hostnames or validate the actual destination IP address at connection time. The CheckAllowedHTTPURL function in securityConfig.go fails to perform DNS resolution, meaning hostnames that resolve to loopback, private, or cloud-metadata addresses (e.g., 169.254.169.254) can bypass the policy. No dial-time hook is installed in the HTTP client created in create.go, so no runtime check occurs either. An attacker who can inject a URL via content fields such as front-matter or CMS inputs can cause the Hugo build process to fetch internal or cloud metadata endpoints. The fetched response body is then embedded into the generated static site output, effectively exfiltrating sensitive internal data through the build artifact itself. This makes it particularly dangerous in CI/CD pipelines with access to cloud metadata services.