Insecure header validation in slim/psr7

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 Graham Campbell 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