CVE-2023-30536 is a medium-severity (CVSS 6.5) CWE-436 vulnerability in slim/psr7. 1 public exploit reference exists, so weaponization risk is real. A fix is available for slim/psr7 — see the affected versions and patch details below.
Insecure header validation in slim/psr7
Exploitation Status
No confirmed exploitation observed yet
- CISA assesses this as automatable — exploitation doesn’t require manual, per-target effort, which raises the odds of mass scanning and opportunistic attacks.
- CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.
Exploitation and automatability from CISA’s SSVC triage for CVE-2023-30536.
EPSS Exploitation Probability
EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.
How urgent is this, really
CVE-2023-30536 plotted by exploitation likelihood (EPSS) against impact (CVSS). The shaded corner — EPSS 50%+ and CVSS 7.0+ — is where this CVE doesn't sit, though severity or exploitability alone can still warrant action.
Where this sits among everything scored
Of 378,567 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Real counts from FIRST.org, not a sample — log-scaled since the landscape is heavily right-skewed.
Real-World Exposure
slim/psr7🐘slim/psr7🐘slim/psr7Real-time download stats are indexed for npm and PyPI packages. This vulnerability affects Packagist packages — download data is not available via public APIs for these ecosystems.
Description
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
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐘Packagist | slim/psr7 | ≥ 1.6&&< 1.6.1 | 1.6.1composer require slim/psr7:^1.6.1 |
| 🐘Packagist | slim/psr7 | ≥ 1.5&&< 1.5.1 | 1.5.1composer require slim/psr7:^1.5.1 |
| 🐘Packagist | slim/psr7 | all versions | 1.4.1composer require slim/psr7:^1.4.1 |
Research use only. For defensive security, authorized penetration testing, and academic research only. Never execute exploit code against systems without explicit written authorization.
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for slim/psr7, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update slim/psr7 to 1.6.1 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2023-30536 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 Security's impact-aware SCA analyses which vulnerable code paths your application actually calls, so a match like CVE-2023-30536 can be triaged on real exposure rather than presence alone.
Tailored to CVE-2023-30536. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is CVE-2023-30536 in your dependencies?
O3 Security finds CVE-2023-30536 across Packagist dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.