Hugo is a static site generator. From v0.161.0, Hugo executes Node tools under Node's permission model, but TailwindCSS — included in the default security.exec.allow list — requires a highly permissive configuration (--allow-addons, --allow-child-process, --allow-worker). As a result, the restrictions intended by the fix for GHSA-x597-9fr4-5857 could still be bypassed, allowing a Node tool invoked during a build to read and write files outside the project's working directory. Affected versions are those after v0.43; the issue was fixed in v0.165.0 by removing tailwindcss from the default security.exec.allow list. Users who do not use TailwindCSS, or who only build trusted sites, are not affected. As a workaround, users can define a restrictive security.exec.allow list in hugo.toml.

Hugo is a static site generator. In versions after v0.123.0 and before v0.165.0, symlinks in parent directories were not dropped during direct resource lookups, allowing path confinement to be bypassed. An attacker who can place — or who convinces a site author to place — a symlink inside a mounted directory (for example, in a locally vendored theme under themes/) can cause functions that perform direct lookups, such as resources.Get and os.ReadFile, to follow that symlink and read files outside the intended project boundaries, disclosing their contents in the built site. Themes mounted as Go modules fetched from GitHub have symlinks stripped on download and are not affected, and multi-directory walks (e.g. content/asset walking) are not affected. This issue is an incomplete-fix follow-up to GHSA-c3wq-j5vh-68rc and GHSA-fw87-fv5r-9fpw; it is fixed in v0.165.0.

Hugo's default fenced-code-block renderer writes attribute values taken from the code-fence info string into the rendered HTML without escaping them. New in markup/internal/attributes/attributes.go converts every attribute value from a byte slice to a string as it is stored, deliberately dropping the escaping that used to happen there, and RenderAttributes in the same file escapes only values that are still byte slices, so its escaping branch is never reached and every value is written verbatim. The function's documentation states that it performs HTML escaping of string attributes, which it does not. A quote inside an attribute value in the info string therefore terminates the attribute and allows a further attribute, including an event handler, to be placed on the wrapper element, and the script runs for every visitor who loads the page. This path is reached under the default configuration, with code fences enabled and without goldmark's unsafe setting or any custom render hook. Attribute names beginning with on are filtered when the attributes are parsed, so injection is achieved through the value rather than the name.

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/resourcefactories/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.

Hugo 0.161.0 placed the Node asset pipelines behind the Node.js permission model so that code running through PostCSS, Babel, or TailwindCSS could not reach the file system outside the project directory. Hugo 0.162.0 added tailwindcss to the AllowChildProcess default in config/security/securityConfig.go, which makes nodePermissionArgs in common/hexec/exec.go append --allow-child-process whenever the tool being launched is named tailwindcss. TailwindCSS loads the site's tailwind.config.js through require at startup, so top-level code in that file executes inside the permitted Node process and can call childprocess to spawn a shell. The spawned process is not a Node process and inherits none of the permission flags, so it runs with the full privileges of the account performing the build. Building a site whose theme, module, or starter template supplies the Tailwind configuration therefore yields arbitrary command execution rather than the confined file access the permission model was introduced to enforce. Hugo 0.165.0 removes tailwindcss from the default security.exec.allow list, so the tool is no longer launched under the default configuration.

Hugo is a static site generator. From 0.60.0 until 0.163.3, Hugo's default code-block renderer wrote the Markdown code-fence language or info-string into the code class="language-…" data-lang="…" wrapper without HTML escaping. A fence info-string containing a quote and a script payload breaks out of the attribute and injects a live script element. This issue is fixed in 0.163.3.

Hugo is a static site generator. From v0.162.0 through v0.163.0, the default security.http.urls policy denies requests to loopback, internal, and cloud-metadata IPv4 literals, but the deny rule only matched dotted-decimal notation, so alternate IPv4 encodings of the same addresses, including integer, hex, or octal, passed the policy. When a template passes an untrusted or data-derived URL to resources.GetRemote and the host platform uses the cgo system resolver, these encodings resolve to the blocked address, allowing build-time server-side requests to loopback and internal services, including the cloud-metadata endpoint in hosted or CI builds; the same check is reused on redirects, so the gap also applies to each redirect hop. This issue is fixed in v0.163.1.