Server Side Template Injection in Gorilla Mux with Cockroachdb

Server Side Template Injection (SSTI) occurs when an attacker can control template input that is later rendered by a server-side templating engine. In a Gorilla Mux application using Cockroachdb, the risk arises when user-supplied data is passed into templates without proper escaping or isolation, and then that data influences database operations such as query construction or metadata handling.

Gorilla Mux is a URL router and dispatcher. If route variables or query parameters are used to select database names, table names, or to dynamically build SQL-like logic before sending statements to Cockroachdb, an attacker may inject template syntax that executes unintended logic during rendering. For example, if a handler uses user input to construct a map passed to a template, and that map is later used in a Cockroachdb query string built via string concatenation, malicious template directives could alter the query structure.

Cockroachdb does not directly process templates, but the application layer does. The combination permits a scenario where unsanitized input reaches a Go template that then builds Cockroachdb statements. If the template executes actions like .Execute on constructed strings that become SQL text, the injection can manifest as unexpected query behavior, metadata leakage, or execution of unintended SQL fragments. This is especially dangerous when the application exposes debug endpoints or administrative routes where template rendering is more permissive.

Real-world patterns include dynamic construction of SELECT or SHOW statements where table or column names are inserted via template variables. Although Cockroachdb supports parameterized queries for values, identifiers such as table names cannot be parameterized in the same way. If an attacker can influence the identifier through a compromised template, they may achieve SQL injection-like effects despite using a parameterized client.

An example vulnerable handler might look like this, where user input flows into template context and then into a Cockroachdb query string:

func tableHandler(w http.ResponseWriter, r *http.Request) {
    vars := mux.Vars(r)
    templateName := vars["table"] // user-influenced
    tmpl, _ := template.New("dynamic").Parse(tableNameTemplate) // template stored or user-provided
    data := map[string]string{"TableName": templateName}
    var sb strings.Builder
    tmpl.Execute(&sb, data)
    query := sb.String()
    rows, err := db.Query(query) // Cockroachdb query built from rendered template
    // handle rows
}
const tableNameTemplate = "SELECT * FROM {{.TableName}}"

In this flow, if the template engine processes additional directives or the input contains template actions, the final query sent to Cockroachdb may diverge from developer intent. Although Cockroachdb will reject malformed SQL, the application may expose internal schema details or error messages that aid further exploitation.

Remediation focuses on strict separation of code and data, avoiding dynamic identifier construction from user input, and enforcing allowlists. When interacting with Cockroachdb from Gorilla Mux handlers, never build SQL strings via template rendering that incorporates untrusted identifiers.

Use parameterized queries for values and avoid interpolating user input into SQL text. For identifiers such as table or column names, implement an allowlist mapping or strict validation. Below is a secure pattern that demonstrates how to handle dynamic table selection safely in a Gorilla Mux route without relying on template rendering for SQL construction.

var allowedTables = map[string]bool{
    "users": true,
    "logs":  true,
    "config": true,
}

func secureTableHandler(w http.ResponseWriter, r *http.Request) {
    vars := mux.Vars(r)
    tableName := vars["table"]
    if !allowedTables[tableName] {
        http.Error(w, "invalid table", http.StatusBadRequest)
        return
    }
    // Use fmt.Sprintf only after validation; prefer static queries when possible.
    query := fmt.Sprintf("SELECT * FROM %s", tableName) // tableName is validated
    rows, err := db.Query(query)
    if err != nil {
        http.Error(w, err.Error(), http.StatusInternalServerError)
        return
    }
    defer rows.Close()
    // process rows
}

If dynamic SQL is necessary, prefer using database features such as information_schema with strict validation rather than runtime string assembly. Additionally, ensure that any template rendering used for presentation does not receive raw user input that could trigger unintended actions. Configure templates with FuncMap restrictions and set missingkey=invalid to prevent accidental map key execution.

For applications that must support plugin-like behavior, isolate dynamic SQL execution behind authenticated and authorized administrative endpoints, and avoid exposing template rendering paths that accept arbitrary input. Regularly review route definitions and handler logic to ensure no user-controlled data reaches Cockroachdb construction logic via intermediate template processing.

Finally, integrate middleBrick to continuously validate that no SSTI pathways exist in your API surface. The scanner checks for template injection risks and maps findings to frameworks such as OWASP API Top 10, helping you maintain secure routing and database interaction patterns without relying on manual code audits.