Hugo is a static site generator. In versions from v0.56.0 through v0.165.x, content files mapped to the text/org media type are rendered without escaping raw HTML: Org export blocks and @@html:...@@ snippets pass HTML through unescaped, resulting in cross-site scripting (XSS) in the generated site. An attacker who can supply or influence a content file under /content or the output of a content adapter can inject scripts that execute in the browsers of visitors to the affected pages. Only pages whose source file or content-adapter output declares the text/org media type are affected, and sites that fully trust all content sources are not impacted. Version v0.166.0 fixes the issue by introducing a security.allowContent allowlist that denies text/org by default; sites that intentionally author Org Mode content can opt back in with [security] allowContent = ['.'].
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 versions 0.75.0 through 0.165.x contain a stored cross-site scripting vulnerability: the syntax highlighter does not escape the lineAnchors option before passing it to Chroma, which writes the value verbatim into the id and href attributes of the generated line-number markup. A crafted lineAnchors value supplied as a Markdown code fence attribute (or passed to the highlight template function) results in unescaped HTML in the rendered page, allowing arbitrary JavaScript to execute in the browsers of visitors to the generated site. This affects sites that build and publish Markdown from untrusted contributors; Hugo's security model otherwise considers content trusted input. Fixed in 0.166.0, where the lineAnchors value is HTML-escaped before being passed to Chroma.
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'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 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 v0.123.0 through v0.163.0, Hugo's virtual filesystem is designed so that files under a mount cannot reach outside the mount tree, but a regression caused RootMappingFs.statRoot to call Stat, which follows symlinks, instead of Lstat, so a direct os.ReadFile "somefile" where somefile was a symlink pointing outside the mount would return the target's contents. This effectively let a symlink planted inside a theme or local mount read arbitrary files reachable to the user running hugo. This issue is fixed in v0.163.1.
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.
Commit: f8b5fa09a6 — Fix prevention of direct symlink reads in resources.Get Affected versions: v0.123.0 through v0.161.1. Earlier versions are not affected. Fixed in: v0.162.0. Severity: Medium. Requires the attacker to be able to place (or convince a site author to place) a symlink inside a mounted directory — for example, inside a locally-vendored theme under themes/. Themes mounted as Go modules from GitHub have symlinks stripped on download and are not affected. Multi-directory walks (e.g. content/asset walking) were not affected either; only direct lookups via resources.Get followed symlinks.
Description. Hugo's virtual filesystem is designed so that files under a mount cannot reach outside the mount tree. A regression introduced in v0.123.0 caused RootMappingFs.statRoot to call Stat (which follows symlinks) instead of Lstat, so a direct resources.Get "somefile" where somefile was a symlink pointing outside the mount would return the target's contents. This effectively let a symlink planted inside a theme or local mount read arbitrary files reachable to the user running hugo.
Mitigation. v0.162.0 calls LstatIfPossible and rejects symlinked entries with os.ErrNotExist, matching the behaviour of pre-v0.123.0 releases and of the directory-walking code paths.
Commit: 86fbb0f7a8 — security: Validate redirects against security.http.urls Affected versions: v0.91.0 (when security.http.urls was introduced) through v0.161.1. Fixed in: v0.162.0. Severity: Only relevant for sites that rely on security.http.urls as a trust boundary — e.g. CI builds that fetch remote resources but want to constrain which hosts can be reached. Not an issue if you fully trust every URL passed to resources.GetRemote.
Description. resources.GetRemote enforces security.http.urls on the URL it is called with, but until v0.162.0 it did not re-validate intermediate URLs on HTTP 3xx redirects. An allowed server (or an attacker controlling its DNS or response) could therefore redirect the request to a host that the policy was meant to forbid — for example, http://localhost/ or an internal IP — and Hugo would fetch from the redirected target. The same bypass also lifted any host-shape restriction the operator had put in place.
Mitigation. v0.162.0 installs a CheckRedirect on the HTTP client used by resources.GetRemote that re-runs security.http.urls on every redirect target and caps the redirect chain at 10 hops. No configuration change is required.
Commit: e41a06447d — Disallow HTML content by default Affected versions: all Hugo versions prior to v0.162.0. Fixed in: v0.162.0. Severity: Low to Medium, depending on threat model. Not an issue if you fully trust every file under /content and every content adapter you load.
Description. Hugo accepts content files in several markup formats. Files mapped to the text/html media type (typically .html files under /content, or pages produced by a content adapter that sets content.mediaType = "text/html") had their body emitted verbatim into the rendered page. A site that ingests HTML content from an untrusted source — for example, a CMS-backed editor, a content adapter pulling from an external API, or an automated import pipeline — could therefore be served stored cross-site scripting.
Mitigation. v0.162.0 introduces a security.allowContent whitelist with text/html denied by default. Sites that intentionally author HTML content can opt back in:
toml [security] allowContent = ['.']
This only affects pages whose source file (or content adapter output) declares an HTML media type; Markdown, AsciiDoc, Org, Pandoc and reStructuredText content is unaffected.
Impact 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.
Patches From v0.161.0, Hugo runs Node tools under Node's permission model with strict defaults: No write access and only read access to the site source directories and files.
Workarounds Block these tools in security.exec.allow.