CVE-2026-48157: Slim/slim Cross-Site Scripting Vulnerability

MODERATE
Advisory Identifier: GHSA-53h4-8rc4-f539
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CVSS 6.1
CWE-79
Published
Advisory Summary

CVE-2026-48157 is a MODERATE (CVSS 6.1) cross-site scripting vulnerability (CWE-79: Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')) affecting Slim/slim libraries in the Packagist ecosystem. The issue involves slim has reflected xss in the htmlerrorrenderer. Remediation is available by upgrading affected packages to version 4.15.2.

CVE-2026-48157 at a Glance

CVE Identifier CVE-2026-48157
GHSA Identifier GHSA-53h4-8rc4-f539
Severity MODERATE
CVSS v3.1 Base Score 6.1
CWE Classification CWE-79: Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')
Affected Product Slim/slim
Package Ecosystem Packagist
Published Date
Last Updated

Security Impact

CVSS: 6.1

The security impact metrics below are parsed directly from the CVSS v3.1 vector string (CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N).

Attack Vector Network (AV:N)
Attack Complexity Low (AC:L)
Privileges Required None (PR:N)
User Interaction Required (UI:R)
Scope Changed (S:C)
Confidentiality Low (C:L)
Integrity Low (I:L)
Availability None (A:N)

How to Fix CVE-2026-48157

To remediate this vulnerability, upgrade all affected Slim/slim dependencies to a patched release. Both direct and transitive dependencies should be checked, as frameworks or security libraries may pull in vulnerable versions transitively.

slim/slim fixed: 4.15.2 
Upgrade slim/slim to 4.15.2
Verify Direct and Transitive Dependencies

Run the following command in your project directory to verify that all resolved dependencies use the patched release: 

inspect dependencies for slim/slim

How to Check if You Are Affected

To determine whether your application is affected by CVE-2026-48157, inspect your project dependencies for Slim/slim:

inspect dependencies for slim/slim

Analyze the terminal output to locate any version of Slim/slim in your dependency tree. If any resolved version matches the vulnerable ranges listed in the table below (for example, versions earlier than 4.15.2), your application is affected.

Note: Verify declared build manifests and deployed runtime container environments.

Technical Details

Vulnerability Mechanism & Technical Analysis

This vulnerability is classified under CWE-79: Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting'), where the product does not neutralize or incorrectly neutralizes user-controllable input before it is placed in output that is used as a web page that is served to other users. In Slim/slim, software state validation or input boundaries are circumvented during processing. Review the official source advisory statement below for specific affected components, classes, and reproduction details.

Source Advisory Statement

### 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](https://github.com/0xEr3n) for reporting this issue. ### Resources - CWE-79: https://cwe.mitre.org/data/definitions/79.html

CVE-2026-48157 Affected Slim/slim Versions

1 component(s)
Fixed Versions:
4.15.2
Product / Package Ecosystem Affected Versions Fixed Version
slim/slim
 Packagist
≥ 4.4.0
< 4.15.2
4.15.2

References

GitHub Advisory / Wiki ADVISORY
https://github.com/slimphp/Slim/security/advisories/GHSA-53h4-8rc4-f539
NVD — CVE-2026-48157 NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-48157
Slim/slim Source Repository REPOSITORY
https://github.com/slimphp/Slim
Slim/slim Release RELEASE
https://github.com/slimphp/Slim/releases/tag/4.15.2

Frequently Asked Questions

What is CVE-2026-48157?
CVE-2026-48157 is a security vulnerability in Slim/slim involving Slim has Reflected XSS in the HtmlErrorRenderer under CWE-79: Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting').
Which Slim/slim versions are affected?
Affected versions include releases prior to 4.15.2 across affected packages: slim/slim.
What version fixes CVE-2026-48157?
Upgrading to 4.15.2 (or the latest patched release for your respective branch) resolves the vulnerability.
Is slim/slim affected?
Yes, slim/slim is affected in releases prior to 4.15.2. Upgrade your dependency to 4.15.2 or later.
What is the CVSS score of CVE-2026-48157?
CVE-2026-48157 has a CVSS v3.1 base score of 6.1 (MODERATE) with vector string CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N.
What CWE is associated with CVE-2026-48157?
CVE-2026-48157 is classified under CWE-79: Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting') (The product does not neutralize or incorrectly neutralizes user-controllable input before it is placed in output that is used as a web page that is served to other users.).
How can I check Packagist dependencies for CVE-2026-48157?
Run the dependency tree command: 'inspect dependencies for slim/slim'. This command lists direct and transitive dependencies in your build configuration so you can verify if a vulnerable version is resolved.
Machine-readable OSV JSON OSV v1.5 Schema
Normalized schema output
View Raw JSON 
{
  "schema_version" : "1.4.0",
  "id" : "GHSA-53h4-8rc4-f539",
  "modified" : "2026-06-23T21:54:06Z",
  "published" : "2026-06-23T21:54:06Z",
  "aliases" : [ "CVE-2026-48157" ],
  "summary" : "Slim has Reflected XSS in the HtmlErrorRenderer",
  "details" : "### Impact\n\nIf 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.\n\nThe vulnerability is present even with `displayErrorDetails = false` as the unescaped title and description are rendered on this error path.\n\nBuilt-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.\n\n### Patches\n\nThe issue is fixed in 4.15.2.\n\n### Workarounds\n\nWithout upgrading, applications can:\n\n- Avoid passing untrusted/request-derived data into `HttpException::setTitle()` and `setDescription()`. Use static, plain-text error copy instead.\n- Register a custom error renderer (an `ErrorRendererInterface` implementation, or a subclass of `HtmlErrorRenderer` that escapes the title and description) for the HTML media type.\n\n### Acknowledgments\n\nSlim is grateful to and thanks GitHub user [0xEr3n](https://github.com/0xEr3n) for reporting this issue.\n\n### Resources\n\n- CWE-79: https://cwe.mitre.org/data/definitions/79.html",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "Packagist",
      "name" : "slim/slim"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "4.4.0"
      }, {
        "fixed" : "4.15.2"
      } ]
    } ],
    "database_specific" : {
      "last_known_affected_version_range" : "<= 4.15.1"
    }
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/slimphp/Slim/security/advisories/GHSA-53h4-8rc4-f539"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-48157"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/slimphp/Slim"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/slimphp/Slim/releases/tag/4.15.2"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-79" ],
    "severity" : "MODERATE",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-06-23T21:54:06Z",
    "nvd_published_at" : "2026-06-15T22:16:17Z"
  }
}