Hugo vulnerabilities

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 a symlink inside a mounted directory can cause functions 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.

Hugo from v0.161.0 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 from v0.60.0 before v0.167.0 contains a stored cross-site scripting vulnerability that allows Markdown content authors to inject HTML by supplying crafted explicit heading IDs. Attackers can break out of the unescaped href attribute in .TableOfContents or .Fragments.ToHTML output to inject elements with event handlers into rendered pages.

Hugo from v0.162.0 before v0.167.0 contains an improper link resolution vulnerability that lets malicious themes or modules expose files outside their root via nested-mount ancestor directories. Attackers controlling a theme can place a symlink or NTFS junction at a virtual ancestor directory, causing resources.Match to list and publish local files during builds.

Hugo from v0.84.0 before v0.167.0 contains a path traversal vulnerability that allows malicious themes or modules to read files outside the project root via ESBuild's fallback resolver in js.Build, js.Batch, and css.Build. Attackers can ship relative imports or symlinks pointing outside the project to bundle any file readable by the build user into published JavaScript or CSS output.

Hugo before v0.167.0 contains a path traversal vulnerability in css.Sass that allows malicious themes or modules to read files outside the project root through the Sass compiler's import fallback. Attackers can ship stylesheets with relative, absolute, or symlinked @import or @use targets to compile readable files into the published site CSS.

Hugo, a static site generator, in versions from v0.56.0 through v0.165.x renders content files mapped to the text/org media type without escaping raw HTML. Org export blocks and @@html:...@@ snippets pass HTML through unescaped, resulting in cross-site scripting (XSS) in the generated site. Only pages whose source file or content-adapter output declares the text/org media type are affected; version v0.166.0 fixes the issue by introducing a security.allowContent allowlist that denies text/org by default.

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, a static site generator, in versions after v0.123.0 and before v0.166.0, has a flaw in its symlink confinement checks. A theme or module in themes/ (or a vendored module) can contain a symlink at a mount root, allowing files behind such a symlink to be read during a site build and published to public/, bypassing the rule that theme and module mount sources must be local paths.

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. Fixed in 0.166.0, where the lineAnchors value is HTML-escaped before being passed to Chroma.

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 code in markup/internal/attributes/attributes.go converts every attribute value from a byte slice to a string, dropping escaping, and RenderAttributes escapes only values that are still byte slices, so its escaping branch is never reached. A quote inside an attribute value can terminate the attribute and allow a further attribute, including an event handler, to be placed on the wrapper element, causing script execution for every visitor who loads the page.

Hugo does not verify the actual IP address the HTTP client connects to when fetching resources via resources.GetRemote. The security.http.urls allowlist only checks the URL text, not the real destination, allowing access to internal resources.

Hugo 0.162.0 added tailwindcss to the default AllowChildProcess list, causing the Node.js process for TailwindCSS to have child process permissions. Top-level code in tailwind.config.js can execute arbitrary commands, bypassing the Node.js permission model.

In Hugo from version 0.123.0 to 0.161.1, a regression made RootMappingFs.statRoot use Stat (follows symlinks) instead of Lstat, allowing a symlink planted in a local mount (e.g. a vendored themes/ theme) to read arbitrary files accessible to the Hugo user via resources.Get.

A vulnerability in Hugo from v0.162.0 to v0.163.0 allows bypassing the security policy that blocks requests to loopback, internal, and cloud-metadata IPv4 addresses. The policy only matched dotted-decimal notation, so alternative IPv4 encodings (integer, hex, octal) bypassed the block. When a template passes an untrusted URL to resources.GetRemote and the host uses the cgo system resolver, these encodings resolve to blocked addresses, enabling SSRF attacks to internal services and cloud-metadata endpoints in hosted or CI builds.

A vulnerability in Hugo (versions 0.123.0 through 0.163.0) allows bypassing virtual filesystem security. A bug in RootMappingFs.statRoot causes symbolic links inside mounted directories to point outside the mount tree, enabling reading arbitrary files accessible to the user running Hugo.

Hugo from version 0.60.0 to 0.163.3 by default rendered Markdown code blocks without proper HTML escaping in class and data-lang attributes. An info-string containing a quote and JavaScript payload could break out of the attribute and inject a live script element.

In Hugo from version 0.91.0 to 0.162.0, the resources.GetRemote function does not re-validate destination URLs after HTTP 3xx redirects, allowing bypass of the security.http.urls policy. An attacker can redirect the request to a forbidden host, and Hugo will fetch from it.

Hugo before version 0.162.0 accepts content files in various markup formats. Files mapped to the text/html media type (e.g., .html files under /content) are emitted verbatim into the rendered page, enabling stored XSS attacks.