CVE-2026-48157
MEDIUMCVE-2026-48157 is a medium-severity (CVSS 6.1) Cross-site Scripting (XSS) vulnerability in slim/slim. O3 Security confirms whether CVE-2026-48157 is actually reachable in your code before you act, and blocks exploitation at runtime until you patch.
Slim has Reflected XSS in the HtmlErrorRenderer
Blast Radius
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
Slim is a PHP micro framework that enables users to write simple web applications and APIs. In versions 4.4.0 through 4.15, 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. The issue has been fixed in 4.15.2. If developers are unable to immediately update their applications, they can work around this issue by avoiding passing untrusted/request-derived data into HttpException::setTitle() and setDescription() and using static, plain-text error copy instead. They should also register a custom error renderer (an ErrorRendererInterface implementation, or a subclass of HtmlErrorRenderer that escapes the title and description) for the HTML media type.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐘Packagist | slim/slim | ≥ 4.4.0&&< 4.15.2 | 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. O3's reachability analysis confirms whether the vulnerable code path is actually invoked in your application, so you act on real exposure instead of every transitive match.
Fix
Update slim/slim to 4.15.2 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-48157 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 pinpoints whether CVE-2026-48157 is reachable in your code and exactly where to fix it, then blocks exploitation in production at runtime until the patched version is deployed.
Tailored to CVE-2026-48157. 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-2026-48157 in your dependencies?
O3 detects CVE-2026-48157 across Packagist dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.