Insecure header validation in slim/psr7

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS

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

EPSS

• CVE-2023-30536: 0.74% estimated exploitation activity in the next 30 days; percentile 54.79 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

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…

Published by the source

18 Apr 2023, 22:20 UTC

Last modified by the source

4 Nov 2023, 05:04 UTC

Source last checked

26 Oct 2026, 14:10 UTC

1. Revision 1 · created · 26 Oct 2026

   Published from ghsa record GHSA-q2qj-628g-vhfw

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# Patch Next advisory brief: CVE-2023-30536

Advisory: Insecure header validation in slim/psr7
IDs: CVE-2023-30536, GHSA-q2qj-628g-vhfw
Record: https://patchnext.com/advisories/cve-2023-30536 (revision 1, source checked 26 Oct 2026, 14:10 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 6.5)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: slim/psr7 1.6.1, 1.5.1, 1.4.1. A vendor fix does not mean a deployment is fixed.

## Affected components
- Packagist slim/psr7: affected >= 1.6, < 1.6.1; >= 1.5, < 1.5.1; < 1.4.1; fixed in 1.4.1, 1.6.1, 1.5.1

## Suggested inspection (read-only)
- Packagist slim/psr7: check the installed version with your package manager.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on slim/psr7.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://github.com/advisories/GHSA-q2qj-628g-vhfw (GitHub-reviewed advisory GHSA-q2qj-628g-vhfw lists affected ranges: Packagist slim/psr7 >=1.6 =1.5 =0 <1.4.1)

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