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64 lines
3.8 KiB
Markdown
64 lines
3.8 KiB
Markdown
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---
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title: Hugo's security model
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description: A summary of Hugo's security model.
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categories: [about]
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keywords: [security,privacy]
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menu:
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docs:
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parent: about
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weight: 50
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weight: 50
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toc: true
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aliases: [/security/]
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---
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## Runtime security
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Hugo produces static output, so once built, the runtime is the browser (assuming the output is HTML) and any server (API) that you integrate with.
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But when developing and building your site, the runtime is the `hugo` executable. Securing a runtime can be [a real challenge](https://blog.logrocket.com/how-to-protect-your-node-js-applications-from-malicious-dependencies-5f2e60ea08f9/).
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**Hugo's main approach is that of sandboxing and a security policy with strict defaults:**
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* Hugo has a virtual file system and only the main project (not third-party components) is allowed to mount directories or files outside the project root.
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* Only the main project can walk symbolic links.
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* User-defined components have read-only access to the filesystem.
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* We shell out to some external binaries to support [Asciidoctor](/content-management/formats/#list-of-content-formats) and similar, but those binaries and their flags are predefined and disabled by default (see [Security Policy](#security-policy)). General functions to run arbitrary external OS commands have been [discussed](https://github.com/gohugoio/hugo/issues/796), but not implemented because of security concerns.
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## Security policy
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Hugo has a built-in security policy that restricts access to [os/exec](https://pkg.go.dev/os/exec), remote communication and similar.
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The default configuration is listed below. Any build using features not in the allow list of the security policy will fail with a detailed message about what needs to be done. Most of these settings are allow lists (string or slice, [Regular Expressions](https://pkg.go.dev/regexp) or `none` which matches nothing).
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{{< code-toggle config=security />}}
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Note that these and other configuration settings in Hugo can be overridden by the OS environment. If you want to block all remote HTTP fetching of data:
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```txt
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HUGO_SECURITY_HTTP_URLS=none hugo
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```
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## Dependency security
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Hugo is built as a static binary using [Go Modules](https://github.com/golang/go/wiki/Modules) to manage its dependencies. Go Modules have several safeguards, one of them being the `go.sum` file. This is a database of the expected cryptographic checksums of all of your dependencies, including transitive dependencies.
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[Hugo Modules](/hugo-modules/) is a feature built on top of the functionality of Go Modules. Like Go Modules, a Hugo project using Hugo Modules will have a `go.sum` file. We recommend that you commit this file to your version control system. The Hugo build will fail if there is a checksum mismatch, which would be an indication of [dependency tampering](https://julienrenaux.fr/2019/12/20/github-actions-security-risk/).
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## Web application security
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These are the security threats as defined by [OWASP](https://en.wikipedia.org/wiki/OWASP).
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For HTML output, this is the core security model:
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<https://pkg.go.dev/html/template#hdr-Security_Model>
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In short:
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Template and configuration authors (you) are trusted, but the data you send in is not.
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This is why you sometimes need to use the _safe_ functions, such as `safeHTML`, to avoid escaping of data you know is safe.
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There is one exception to the above, as noted in the documentation: If you enable inline shortcodes, you also say that the shortcodes and data handling in content files are trusted, as those macros are treated as pure text.
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It may be worth adding that Hugo is a static site generator with no concept of dynamic user input.
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For content, the default Markdown renderer is [configured](/getting-started/configuration-markup) to remove or escape potentially unsafe content. This behavior can be reconfigured if you trust your content.
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