Overview
SSRF vulnerabilities in web services can enable attackers to make the server fetch internal or protected resources by following a provided URL. In Echo-based apps, this commonly arises when a handler takes a URL from a client and fetches it server-side without validation, potentially exposing internal networks, cloud metadata endpoints, or other sensitive services.
In Echo, SSRF tends to manifest when a route reads a URL from query parameters or form fields and uses the Go HTTP client directly (for example with http.Get). Because the request originates from the server, the attacker can leverage your service as a proxy, reaching resources that would be blocked if accessed directly by the client.
Remediation focuses on default-denial and defense-in-depth: validate and constrain input, implement a strict allowlist of destinations, enforce timeouts and size limits, and isolate external fetches behind a controlled fetcher. After applying these patterns, test with common SSRF vectors and monitor for anomalous outbound activity.
Code Fix Example
Echo API Security Remediation
package main\n\nimport (\n \"io\"\n \"net\"\n \"net/http\"\n \"net/url\"\n \"time\"\n \"github.com/labstack/echo/v4\"\n)\n\nfunc main() {\n e := echo.New()\n e.GET(\"/fetch\", vulnerableFetch)\n e.GET(\"/fetch-fixed\", fixedFetch)\n e.Start(\":8080\")\n}\n\nfunc vulnerableFetch(c echo.Context) error {\n target := c.QueryParam(\"url\")\n resp, err := http.Get(target)\n if err != nil {\n return c.String(http.StatusBadGateway, \"error fetching URL\")\n }\n defer resp.Body.Close()\n body, _ := io.ReadAll(resp.Body)\n return c.String(http.StatusOK, string(body))\n}\n\nfunc fixedFetch(c echo.Context) error {\n raw := c.QueryParam(\"url\")\n u, err := url.Parse(raw)\n if err != nil {\n return c.String(http.StatusBadRequest, \"invalid url\")\n }\n if !isAllowed(u) {\n return c.String(http.StatusForbidden, \"url not allowed\")\n }\n client := &http.Client{Timeout: 5 * time.Second, Transport: &http.Transport{Proxy: http.ProxyFromEnvironment}}\n resp, err := client.Get(raw)\n if err != nil {\n return c.String(http.StatusBadGateway, \"fetch failed\")\n }\n defer resp.Body.Close()\n body, _ := io.ReadAll(resp.Body)\n return c.String(http.StatusOK, string(body))\n}\n\nfunc isAllowed(u *url.URL) bool {\n if u.Scheme != \"http\" && u.Scheme != \"https\" {\n return false\n }\n host := u.Hostname()\n ip := net.ParseIP(host)\n if ip != nil {\n if isPrivateIP(ip) {\n return false\n }\n return true\n }\n ips, err := net.LookupIP(host)\n if err != nil {\n return false\n }\n for _, ip := range ips {\n if isPrivateIP(ip) {\n return false\n }\n }\n return true\n}\n\nfunc isPrivateIP(ip net.IP) bool {\n if ip4 := ip.To4(); ip4 != nil {\n switch {\n case ip4[0] == 10:\n return true\n case ip4[0] == 172 && ip4[1] >= 16 && ip4[1] <= 31:\n return true\n case ip4[0] == 192 && ip4[1] == 168:\n return true\n }\n return false\n }\n if ip.To16() != nil {\n if ip[0] == 0xfc || ip[0] == 0xfd {\n return true\n }\n }\n return false\n}\n