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Merged
riramar merged 1 commit into from
Jan 14, 2025
Merged

Add info about base-uri #213

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Binary file added assets/misc/demo_csp_bypass_due_to_no_base_uri_directive.mp4
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14 changes: 11 additions & 3 deletions tab_bestpractices.md
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Expand Up @@ -42,7 +42,7 @@ The following section proposes a configuration for the [actively supported and w
| Strict-Transport-Security | `max-age=31536000; includeSubDomains` |
| X-Frame-Options | `deny` |
| X-Content-Type-Options | `nosniff` |
| Content-Security-Policy | `default-src 'self'; form-action 'self'; object-src 'none'; frame-ancestors 'none'; upgrade-insecure-requests; block-all-mixed-content` |
| Content-Security-Policy | `default-src 'self'; form-action 'self'; base-uri 'self'; object-src 'none'; frame-ancestors 'none'; upgrade-insecure-requests; block-all-mixed-content` |
| X-Permitted-Cross-Domain-Policies | `none` |
| Referrer-Policy | `no-referrer` |
| Clear-Site-Data | `"cache","cookies","storage"` |
Expand Down Expand Up @@ -344,22 +344,30 @@ This section describes some points, to keep in mind, during the creation of a [C

🚩 Not every **[directives](https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Content-Security-Policy#directives)** fallback to the **[default-src](https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Content-Security-Policy/default-src)** directive when it is not specified in the CSP policy.

## Directive form-action
### Directive form-action

👀 It is the case for the **[form-action](https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Content-Security-Policy/form-action)** directive. Therefore, an html form can be used to bypass the CSP in place when the `form-action` is not defined.

📺 This [demonstration video](assets/misc/demo_csp_bypass_due_to_no_form_action_directive.mp4) show an example.

💡 Therefore, ensure to always specify the `form-action` directive in a CSP policy to at least, the `'self'` value, to allow forms only on the current domain.

## Directive frame-ancestors
### Directive frame-ancestors

👀 It is the case for the **[frame-ancestors](https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Content-Security-Policy/frame-ancestors)** directive. Therefore, IF it is not defined **AND** IF the header [X-Frame-Options](https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/X-Frame-Options) is not/incorrectly specified then the current domain can be embedded into a frame.

📺 This [demonstration video](assets/misc/demo_csp_bypass_due_to_no_frame_ancestors_directive.mp4) show an example.

💡 Therefore, ensure to always specify the `frame-ancestors` directive in a CSP policy to at least, the `'none'` value, to deny the current domain to be "framed".

### Directive base-uri

👀 It is the case for the **[base-uri](https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Content-Security-Policy/base-uri)** directive.

📺 This [demonstration video](assets/misc/demo_csp_bypass_due_to_no_base_uri_directive.mp4) show an example.

💡 Therefore, ensure to always specify the `base-uri` directive in a CSP policy to at least, the `'self'` value, to only allow the current domain to be specified as the document's base URI via a `<base href="..." />` html tag.

## Support for a large CSP policy

Tests were performed to identify if any limitation was in place, regarding the definition and usage of a large CSP policy. Tests were performed against the following browsers:
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