Gohugo vulnerabilities

Hugo versions from v0.162.0 before v0.166.0 contain a case-sensitive validation flaw in the security.http.urls IP-literal deny rule that allows attackers to bypass restrictions. Attackers can use mixed-case URL schemes in resources.GetRemote calls to fetch from restricted IP addresses like localhost.

Hugo is a static site generator. In versions after v0.123.0 and before v0.166.0, Hugo's symlink confinement checks stopped at the mount root itself, so a theme or module checked into themes/ (or a vendored module) could contain a symlink at a mount root (for example themes/mytheme/assets -> /some/dir/outside). Files behind such a symlink were readable during a site build through resources.Get, resources.Match and similar functions, and could be published to public/ via static mounts, bypassing the rule that theme and module mount sources must be local paths. Modules fetched via Go modules are not affected because Go module zips cannot contain symlinks, and this is not an escalation for the main project, which may already mount absolute paths by configuration. Fixed in v0.166.0, where symlinked mount roots and symlinked directories between the mount root and the module directory are treated as non-existent for all modules. As a workaround, inspect themes/ and vendored modules for symlinks at mount roots before building, or replace symlinks with explicit mounts.

Hugo versions from v0.161.0 through v0.165.0 run Node.js tools (css.PostCSS, css.TailwindCSS, js.Babel) under the Node.js permission model to restrict file system reads to the project directory and configured mounts. Because the Node.js permission model validates only the lexical path and follows symbolic links that point outside the allowed set, Hugo did not detect symlinks escaping the sandbox. An attacker who can contribute content to a Hugo project (for example via a pull request) can commit a symlink such as assets/css/x.css -> /etc/passwd together with a PostCSS plugin that reads it, allowing any file readable by the Hugo build process to be disclosed and potentially embedded in the published site. This affects builds using the default security configuration; projects that do not invoke Node.js tools are unaffected. Fixed in v0.166.0, which scans allowed paths and fails the build when a symbolic link resolves outside them.

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 child_process 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 0.43 to before 0.161.0, when building a Hugo site that uses Node-based asset pipelines (PostCSS, Babel, TailwindCSS), Hugo invoked the configured Node tools without restrictions on file system access. As a result, executing hugo against an untrusted site could allow code running through these tools to read or write files outside the project's working directory. Users who do not use PostCSS, Babel, or TailwindCSS, or who only build trusted sites, are not affected. This vulnerability is fixed in 0.161.0.