GHSA-53h4-8rc4-f539 — slim/slim
MEDIUMGHSA-53h4-8rc4-f539 is a medium-severity (CVSS 6.1) Cross-site Scripting (XSS) vulnerability in slim/slim. A fix is available for slim/slim — see the affected versions and patch details below.
Slim has Reflected XSS in the HtmlErrorRenderer
Exploitation Status
No confirmed exploitation observed yet
- 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 GHSA-53h4-8rc4-f539.
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
GHSA-53h4-8rc4-f539 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 377,333 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/slimReal-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
If an application uses HttpException::setTitle() and/or setDescription() to include untrusted/request-derived data in the error title or description (e.g. "No products found matching '{$query}'."), an attacker could inject arbitrary HTML/JavaScript that executes in the victim's browser when they encounter an HTML error page generated by Slim.
The vulnerability is present even with displayErrorDetails = false as the unescaped title and description are rendered on this error path.
Built-in exceptions (HttpNotFoundException, HttpBadRequestException, etc.) ship plain-text defaults, so a vanilla Slim app with no user code is not exploitable. Only applications that feed untrusted data into setTitle() and/or setDescription() are affected.
Patches
The issue is fixed in 4.15.2.
Workarounds
Without upgrading, applications can:
- Avoid passing untrusted/request-derived data into
HttpException::setTitle()andsetDescription(). Use static, plain-text error copy instead. - Register a custom error renderer (an
ErrorRendererInterfaceimplementation, or a subclass ofHtmlErrorRendererthat escapes the title and description) for the HTML media type.
Acknowledgments
Slim is grateful to and thanks GitHub user 0xEr3n for reporting this issue.
Resources
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐘Packagist | slim/slim | ≥ 4.4.0&&< 4.15.2 | 4.15.2composer require slim/slim:^4.15.2 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for slim/slim, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update slim/slim to 4.15.2 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-53h4-8rc4-f539 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 GHSA-53h4-8rc4-f539 can be triaged on real exposure rather than presence alone.
Tailored to GHSA-53h4-8rc4-f539. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is GHSA-53h4-8rc4-f539 in your dependencies?
O3 Security finds GHSA-53h4-8rc4-f539 across Packagist dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.