GHSA-q2qj-628g-vhfw

### Impact

An attacker could sneak in a newline (`\n`) into both the header names and values. While the specification states that `\r\n\r\n` is used to terminate the header list, many servers in the wild will also accept `\n\n`. An attacker that is able to control the header names that are passed to Slilm-Psr7 would be able to intentionally craft invalid messages, possibly causing application errors or invalid HTTP requests being sent out with an PSR-18 HTTP client. The latter might present a denial of service vector if a remote service’s web application firewall bans the application due to the receipt of malformed requests.

### Patches

The issue is patched in 1.6.1, 1.5.1, and 1.4.1.

### Workarounds

In Slim-Psr7 prior to 1.6.1, 1.5.1, and 1.4.1, validate HTTP header keys and/or values, and if using user-supplied values, filter them to strip off leading or trailing newline characters before calling withHeader().

### Acknowledgments

We are very grateful to and thank <a href="https://gjcampbell.co.uk/">Graham Campbell</a> for reporting and working with us on this issue.

### References

* Guzzle: CVE-2023-29197, with advisory GHSA-wxmh-65f7-jcvw * Laminas Diactoros: CVE-2023-29530, with advisory GHSA-xv3h-4844-9h36 * https://www.rfc-editor.org/rfc/rfc7230#section-3.2.4