CVE-2023-30536

Insecure header validation in slim/psr7

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

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.

CVE-2023-30536 has a CVSS score of 6.5 (Medium). The vector is network-reachable, no privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (1.6.1, 1.5.1, 1.4.1); upgrading removes the vulnerable code path.

Kodem intelligence

Already deployed Kodem?

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

1. What is CVE-2023-30536? CVE-2023-30536 is a medium-severity security vulnerability in slim/psr7 (composer), affecting versions >= 1.6, < 1.6.1. It is fixed in 1.6.1, 1.5.1, 1.4.1.
2. How severe is CVE-2023-30536? CVE-2023-30536 has a CVSS score of 6.5 (Medium). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
3. Which versions of slim/psr7 are affected by CVE-2023-30536? slim/psr7 (composer) versions >= 1.6, < 1.6.1 is affected.
4. Is there a fix for CVE-2023-30536? Yes. CVE-2023-30536 is fixed in 1.6.1, 1.5.1, 1.4.1. Upgrade to this version or later.
5. Is CVE-2023-30536 exploitable, and should I be worried? Whether CVE-2023-30536 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
6. What actually determines whether CVE-2023-30536 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
7. How do I fix CVE-2023-30536?
   • Upgrade slim/psr7 to 1.6.1 or later
   • Upgrade slim/psr7 to 1.5.1 or later
   • Upgrade slim/psr7 to 1.4.1 or later