GHSA-r2x7-427f-rq69: Github.com/lin snow/ech0 Ech0 Has SSRF Vulnerability

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-r2x7-427f-rq69",
  "modified" : "2026-04-10T19:49:49Z",
  "published" : "2026-04-10T19:49:48Z",
  "aliases" : [ ],
  "summary" : "Ech0 has SSRF via DNS Resolution Bypass in Webhook URL Validation",
  "details" : "## Summary\n\nThe `validateWebhookURL` function in `webhook_setting_service.go` attempts to block webhooks targeting private/internal IP addresses, but only checks literal IP strings via `net.ParseIP()`. Hostnames that DNS-resolve to private IPs (e.g., `169.254.169.254.nip.io`, `10.0.0.1.nip.io`) bypass all checks, allowing an admin to create webhooks that make server-side requests to internal network services and cloud metadata endpoints.\n\n## Details\n\nThe vulnerability is in `validateWebhookURL` (`internal/service/setting/webhook_setting_service.go:180-199`):\n\n```go\nfunc validateWebhookURL(rawURL string) error {\n    parsed, err := url.Parse(rawURL)\n    // ...\n    host := strings.ToLower(parsed.Hostname())\n    if host == \"\" || host == \"localhost\" || strings.HasSuffix(host, \".local\") {\n        return errors.New(commonModel.INVALID_WEBHOOK_URL)\n    }\n    if ip := net.ParseIP(host); ip != nil {  // <-- returns nil for hostnames\n        if ip.IsLoopback() || ip.IsPrivate() || ip.IsLinkLocalMulticast() ||\n            ip.IsLinkLocalUnicast() || ip.IsUnspecified() {\n            return errors.New(commonModel.INVALID_WEBHOOK_URL)\n        }\n    }\n    return nil  // hostname passes all checks unchecked\n}\n```\n\n`net.ParseIP(\"169.254.169.254.nip.io\")` returns `nil` because it is not a literal IP address. The entire private IP check block is skipped, and the function returns `nil` (valid).\n\nBoth HTTP clients that execute webhook requests use standard `http.Client` / `http.Transport` with no custom `DialContext` to verify resolved IPs:\n\n- **TestWebhook** (`webhook_setting_service.go:169`): `&http.Client{Timeout: 5 * time.Second}`\n- **Dispatcher** (`dispatcher.go:51-58`): `&http.Client{...Transport: &http.Transport{...}}` — no custom dialer\n\nThe `Dispatcher.HandleObservation` (`dispatcher.go:67-81`) iterates all active webhooks and dispatches without re-validating URLs, so a stored malicious webhook triggers SSRF on every application event.\n\n**Execution flow:**\n1. Admin calls POST `/api/webhook` with URL `http://169.254.169.254.nip.io/latest/meta-data/`\n2. `CreateWebhook` → `validateWebhookURL` → `net.ParseIP` returns nil → passes validation\n3. Webhook stored in database with `is_active: true`\n4. On any echo event → `Dispatcher.HandleObservation` → `Dispatch` → `SendWithRetry` → DNS resolves `169.254.169.254.nip.io` to `169.254.169.254` → POST to cloud metadata endpoint\n\n## PoC\n\n```bash\n# Step 1: Create a webhook targeting cloud metadata via DNS rebinding\ncurl -X POST http://localhost:8080/api/webhook \\\n  -H 'Authorization: Bearer <admin-jwt>' \\\n  -H 'Content-Type: application/json' \\\n  -d '{\"name\":\"ssrf-probe\",\"url\":\"http://169.254.169.254.nip.io/latest/meta-data/\",\"secret\":\"\",\"is_active\":true}'\n\n# Step 2: Trigger SSRF via test endpoint\ncurl -X POST http://localhost:8080/api/webhook/<webhook-id>/test \\\n  -H 'Authorization: Bearer <admin-jwt>'\n\n# The server makes an HTTP POST to 169.254.169.254 (AWS metadata).\n# net.ParseIP(\"169.254.169.254.nip.io\") returns nil, skipping all IP checks.\n# Delivery status and error messages reveal connectivity information.\n\n# For internal network scanning:\n# http://10.0.0.1.nip.io:8080/\n# http://127.0.0.1.nip.io:6379/\n\n# With is_active:true, every application event automatically dispatches\n# to the SSRF target via Dispatcher.HandleObservation (no re-validation).\n```\n\n## Impact\n\n- **Cloud metadata access:** An admin can reach cloud instance metadata endpoints (AWS `169.254.169.254`, GCP, Azure) to steal IAM credentials, instance identity tokens, and configuration data.\n- **Internal network probing:** Webhooks can scan internal services by observing delivery status (`success`/`failed`) and error messages, mapping internal network topology.\n- **Persistent SSRF:** Active webhooks fire on every application event via the Dispatcher, creating ongoing SSRF without further admin interaction.\n- **Scope escalation:** Impact escapes the application's security boundary to affect internal infrastructure, despite the application explicitly attempting to prevent this.\n\n## Recommended Fix\n\nReplace the hostname-only check with a custom `net.Dialer` that resolves DNS and validates the resolved IP before connecting. Apply this to both HTTP clients:\n\n```go\nimport \"net\"\n\nfunc safeDialContext(ctx context.Context, network, addr string) (net.Conn, error) {\n    host, port, err := net.SplitHostPort(addr)\n    if err != nil {\n        return nil, err\n    }\n    ips, err := net.DefaultResolver.LookupIPAddr(ctx, host)\n    if err != nil {\n        return nil, err\n    }\n    for _, ip := range ips {\n        if ip.IP.IsLoopback() || ip.IP.IsPrivate() || ip.IP.IsLinkLocalUnicast() ||\n            ip.IP.IsLinkLocalMulticast() || ip.IP.IsUnspecified() {\n            return nil, fmt.Errorf(\"resolved IP %s is not allowed\", ip.IP)\n        }\n    }\n    dialer := &net.Dialer{Timeout: 5 * time.Second}\n    return dialer.DialContext(ctx, network, addr)\n}\n\n// Use in both TestWebhook and Dispatcher:\nclient := &http.Client{\n    Timeout: 5 * time.Second,\n    Transport: &http.Transport{\n        DialContext: safeDialContext,\n    },\n}\n```\n\nThis ensures resolved IPs are checked against the private range blocklist regardless of hostname used.",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:C/C:L/I:L/A:N"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "Go",
      "name" : "github.com/lin-snow/ech0"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "4.4.3"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/lin-snow/Ech0/security/advisories/GHSA-r2x7-427f-rq69"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/lin-snow/Ech0"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/lin-snow/Ech0/releases/tag/v4.4.3"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-918" ],
    "severity" : "MODERATE",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-04-10T19:49:48Z",
    "nvd_published_at" : null
  }
}