CVE-2023-30536: slim/psr7 is a PSR-7 implementation for use with Slim 4. In versions prior to 1.6.1 an attacker could sneak in a newline (\n) into both the header nam...

Description

slim/psr7 is a PSR-7 implementation for use with Slim 4. In versions prior to 1.6.1 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. The issue has been patched in version 1.6.1. There are no known workarounds to this issue. Users are advised to upgrade.

Metrics

CVSS 3.1

6.5/10

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:L

EPSS Probability

0.74%

50.0th percentile

Probability of exploitation in the next 30 days. Learn more

Weakness Enumeration

CWE-436

Affected Software

Vendor	Product	Versions
Slimframework	Slim Psr-7	< 1.6.1

References

https://github.com/slimphp/Slim-Psr7/commit/ed1d553225dd190875d8814c47460daed4b550bbPatch
https://github.com/slimphp/Slim-Psr7/security/advisories/GHSA-q2qj-628g-vhfwVendor Advisory
https://www.rfc-editor.org/rfc/rfc7230#section-3.2.4Technical Description
https://github.com/slimphp/Slim-Psr7/commit/ed1d553225dd190875d8814c47460daed4b550bbPatch
https://github.com/slimphp/Slim-Psr7/security/advisories/GHSA-q2qj-628g-vhfwVendor Advisory
https://www.rfc-editor.org/rfc/rfc7230#section-3.2.4Technical Description

Timeline

Published: Apr 17, 2023
Last Modified: Jun 17, 2026
Status: Modified

Frequently Asked Questions

What is CVE-2023-30536?

slim/psr7 is a PSR-7 implementation for use with Slim 4. In versions prior to 1.6.1 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. The issue has been patched in version 1.6.1. There are no known workarounds to this issue. Users are advised to upgrade.

How severe is CVE-2023-30536?

CVE-2023-30536 has a CVSS score of 6.5/10 (MEDIUM severity). The EPSS model estimates a 0.74% probability of exploitation in the next 30 days.

How do I fix CVE-2023-30536?

Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.