GHSA-xq52-rv6w-397c

### 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