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MEDIUM severity

Slim has Reflected XSS in the HtmlErrorRendererGHSA-53h4-8rc4-f539

MEDIUM

GHSA-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.

Also known asCVE-2026-48157
Published
Updated
Affected
1 pkg
Patched
1 / 1
Exploits
None indexed
Exploitation data as of Nov 7, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

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

via FIRST.org ↗
0.2%probability of exploitation in next 30 days
Lower Risk0.00%
Lower risk than most CVEs6th percentile — riskier than 6% of all scored CVEsHighest risk
0.00%0.22%0.44%0.67%0.2%0.2%Jul 26Nov 26

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

How urgent is this, really

Where this sits among everything scored

Real-World Exposure

1 pkg affected
🐘slim/slim

Real-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() and setDescription(). Use static, plain-text error copy instead.
  • Register a custom error renderer (an ErrorRendererInterface implementation, or a subclass of HtmlErrorRenderer that 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

1 total 1 fixed
EcosystemPackageVulnerable rangeFix
🐘Packagistslim/slim≥ 4.4.0&&< 4.15.24.15.2composer require slim/slim:^4.15.2

Detection & mitigation playbook

Open-source dependency

  1. Detect

    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.

  2. 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.

  3. Workarounds

    Escape or sanitise the affected output on the server side rather than relying on client-side filtering, and add a Content-Security-Policy that blocks inline script execution so injected markup cannot run even if it reaches the page.

Frequently Asked Questions

### 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
O3 Security · Impact-Aware SCA

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Slim has Reflected XSS in the HtmlErrorRenderer