content_security_policy
Type | String |
---|---|
Mandatory | No |
Manifest version | 2 or higher |
Example | Manifest V2:
json
json
|
Extensions have a content security policy (CSP) applied to them by default. The default policy restricts the sources from which extensions can load code (such as <script> resources) and disallows potentially unsafe practices such as the use of eval()
. See Default content security policy to learn more about the implications of this.
You can use the "content_security_policy"
manifest key to loosen or tighten the default policy. This key is specified in the same way as the Content-Security-Policy HTTP header. See Using Content Security Policy for a general description of CSP syntax.
For example, you can use this key to:
- Restrict permitted sources for other types of content, such as images and stylesheets, using the appropriate policy directive.
- Allow the extension to take advantage of WebAssembly by including the
'wasm-unsafe-eval'
source in thescript-src
directive. - Loosen the default
script-src
policies (Manifest V2 only):- Allow the extension to load scripts from outside its package by supplying their URL in the
script-src
directive. - Allow the extension to execute inline scripts by supplying the hash of the script in the
script-src
directive. - Allow the extension to use
eval()
and similar features by including'unsafe-eval'
in thescript-src
directive.
- Allow the extension to load scripts from outside its package by supplying their URL in the
There are restrictions on the policy you can specify with this manifest key:
- The
script-src
directive must include at least the'self'
keyword and may only contain secure sources. The set of permitted secure sources differs between Manifest V2 and Manifest V3. - The policy may include
default-src
alone (withoutscript-src
) if its sources meet the requirement for thescript-src
directive. - The
object-src
keyword may be required, see object-src directive for details. - Directives that reference code –
script-src
,script-src-elem
,worker-src
, anddefault-src
(if used as a fallback) – share the same secure source requirement. There are no restrictions on CSP directives that cover non-script content, such asimg-src
.
In Manifest V3, all CSP sources that refer to external or non-static content are forbidden. The only permitted values are 'none'
, 'self'
, and 'wasm-unsafe-eval'
.
In Manifest V2, a source for a script directive is considered secure if it meets these criteria:
- Wildcard hosts are not permitted, such as
"script-src 'self' *"
. - Remote sources must use
https:
schemes. - Remote sources must not use wildcards for any domains in the public suffix list (so
*.co.uk
and*.blogspot.com
are not allowed, although*.foo.blogspot.com
is permitted). - All sources must specify a host.
- The only permitted schemes for sources are
blob:
,filesystem:
,moz-extension:
,https:
, andwss:
. - The only permitted keywords are:
'none'
,'self'
,'unsafe-eval'
, and'wasm-unsafe-eval'
.
object-src directive
The
directive may be required in some browsers that support obsolete plugins and should be set to a secure source such as object-src
'none'
if needed. This may be necessary for browsers up until 2022.
- In Firefox,
"object-src"
it optional from Firefox 106. In earlier versions, if"object-src"
isn't specified,"content_security_policy"
is ignored and the default CSP used. - In Chrome,
"object-src"
is required. If it's missing or deemed insecure, the default ("object-src 'self'"
) is used and a warning message logged. - In Safari, there is no requirement for
"object-src"
.
See W3C WebExtensions Community Group issue 204, Remove object-src from the CSP, for more information.
Manifest V2 syntax
In Manifest V2, there is one content security policy specified against the key like this:
"content_security_policy": "default-src 'self'"
Manifest V3 syntax
In Manifest V3, the content_security_policy
key is an object that may have any of these properties, all optional:
Name | Type | Description |
---|---|---|
extension_pages |
String |
The content security policy used for extension pages. The script-src and worker-src directives may only have these values:
|
sandbox |
String |
The content security policy used for sandboxed extension pages. |
Examples
Valid examples
Note: Valid examples demonstrate the correct use of keys in CSP. However, extensions with 'unsafe-eval', remote script, blob, or remote sources in their CSP are not allowed for Firefox extensions per the add-on policies and due to significant security issues.
Note: Some examples include the
directive, which provides backward compatibility for older browser versions. See object-src directive for more details.object-src
Require that all types of content should be packaged with the extension:
- Manifest V2
json
"content_security_policy": "default-src 'self'"
- Manifest V3
json
"content_security_policy": { "extension_pages": "default-src 'self'" }
Allow remote scripts from "https://example.com":
- Manifest V2
json
"content_security_policy": "script-src 'self' https://example.com; object-src 'self'"
- Manifest V3 does not allow remote URLs in
script-src
ofextension_pages
.
Allow remote scripts from any subdomain of "jquery.com":
- Manifest V2
json
"content_security_policy": "script-src 'self' https://*.jquery.com; object-src 'self'"
- Manifest V3 does not allow remote URLs in
script-src
ofextension_pages
.
Allow eval()
and friends:
- Manifest V2
json
"content_security_policy": "script-src 'self' 'unsafe-eval'; object-src 'self';"
- Manifest V3 does not allow
'unsafe-eval'
inscript-src
.
Allow the inline script: "<script>alert('Hello, world.');</script>"
:
- Manifest V2
json
"content_security_policy": "script-src 'self' 'sha256-qznLcsROx4GACP2dm0UCKCzCG+HiZ1guq6ZZDob/Tng='; object-src 'self'"
- Manifest V3 does not allow CSP hashes in
script-src
ofextension_pages
.
Keep the rest of the policy, but also require that images should be packaged with the extension:
- Manifest V2
json
"content_security_policy": "script-src 'self'; object-src 'self'; img-src 'self'"
- Manifest V3
json
"content_security_policy": { "extension_pages": "script-src 'self'; img-src 'self'" }
Enable the use of WebAssembly:
-
Manifest V2
For backward compatibility, Manifest V2 extensions in Firefox can use WebAssembly without the use of
'wasm-unsafe-eval'
. However, this behavior isn't guaranteed. See Firefox bug 1770909. Extensions using WebAssembly are therefore encouraged to declare'wasm-unsafe-eval'
in their CSP. See WebAssembly on the Content Security Policy page for more information.json"content_security_policy": "script-src 'self' 'wasm-unsafe-eval'"
- Manifest V3
json
"content_security_policy": { "extension_pages": "script-src 'self' 'wasm-unsafe-eval'" }
Invalid examples
Policy that omits the "object-src"
directive:
"content_security_policy": "script-src 'self' https://*.jquery.com;"
However, this is only invalid in browsers that support obsolete plugins. See object-src directive for more details..
Policy that omits the "self"
keyword in the "script-src"
directive:
"content_security_policy": "script-src https://*.jquery.com; object-src 'self'"
Scheme for a remote source is not https
:
"content_security_policy": "script-src 'self' http://code.jquery.com; object-src 'self'"
Wildcard is used with a generic domain:
"content_security_policy": "script-src 'self' https://*.blogspot.com; object-src 'self'"
Source specifies a scheme but no host:
"content_security_policy": "script-src 'self' https:; object-src 'self'"
Directive includes the unsupported keyword 'unsafe-inline'
:
"content_security_policy": "script-src 'self' 'unsafe-inline'; object-src 'self'"
Browser compatibility
BCD tables only load in the browser