Server Side Template Injection in Buffalo with Cockroachdb

Server Side Template Injection (SSTI) occurs when an attacker can inject template directives that are executed on the server. In a Buffalo application using Cockroachdb as the backend, the risk arises when user-controlled input is passed into template rendering without proper escaping or validation, and the application logic interacts with Cockroachdb queries that may reflect or store that input.

Buffalo uses the built-in html/template package by default, which provides automatic escaping for HTML contexts. However, if a developer uses .Sprintf, template.HTML, or custom template functions to construct dynamic SQL strings or render user input directly into JavaScript, the escaping can be bypassed. When that tainted data is later used in a Cockroachdb query—such as building a dynamic WHERE clause or inserting into a log table—the injected content may be interpreted as code or commands rather than data.

Cockroachdb’s wire protocol and SQL dialect are compatible with PostgreSQL, and certain patterns—such as using placeholders incorrectly or concatenating identifiers—can amplify the impact of SSTI. For example, if a handler constructs a query like "SELECT * FROM accounts WHERE id = '" + userInput + "'" and passes it to Cockroachdb, an attacker could inject additional SQL fragments. Even if the query uses placeholders, improper handling of template variables before reaching the database can still expose internal data structures or error messages that aid further exploitation.

Consider a scenario where a Buffalo handler renders a user profile page and embeds the user’s display name into a JavaScript block without escaping:

// handlers/user.go
func UserShow(c buffalo.Context) error {
    var user models.User
    if err := c.Params().Bind(&user); err != nil {
        return err
    }
    c.Set("profileName", user.DisplayName) // unsanitized user input
    return c.Render(200, r.HTML("user/show.html"))
}

In the template, if {{ .profileName }} is placed inside an HTML attribute without proper context escaping (e.g., inside an onerror handler), it can lead to reflected XSS or be stored in Cockroachdb and later rendered in an admin dashboard, creating a stored vector. The combination of Buffalo’s rapid scaffolding and Cockroachdb’s distributed nature means that misconfigured templates can propagate tainted data across services before validation occurs.

Additionally, if the application uses code generation or dynamic routing that pulls table or column names from user input to query Cockroachdb, SSTI can pivot into injection against the database itself. This is especially relevant when OpenAPI specs are scanned by middleBrick: unchecked parameters that reach the database layer may expose endpoints where template-driven SQL construction bypasses prepared statements.

Remediation focuses on ensuring that user input is never interpreted as code, both in templates and in SQL sent to Cockroachdb. Follow these concrete patterns when building Buffalo handlers and models.

• Always use parameterized queries with ? placeholders and the sqlx or gorm ORM provided by Buffalo, never string concatenation for SQL fragments involving Cockroachdb.

// Correct: parameterized query to Cockroachdb
query := "SELECT id, email FROM accounts WHERE team_id = ? AND status = ?"
rows, err := c.Connection().Query(query, teamID, status)
if err != nil {
    return err
}
defer rows.Close()

• When dynamic sorting or filtering is required, validate against a strict allowlist before using identifiers in SQL; do not interpolate raw user strings into ORDER BY or GROUP BY.

// Allowlist-based safe ordering
validOrder := map[string]string{
    "created": "created_at",
    "name":    "name",
}
sortField, ok := validOrder[userInputSort]
if !ok {
    sortField = "created_at"
}
query := fmt.Sprintf("SELECT * FROM accounts ORDER BY %s", sortField) // safe: sortField is from allowlist

• In templates, rely on Buffalo’s default escaping and explicitly set context when using custom delimiters or JavaScript. Use {{ .profileName | html }} or ensure the template is parsed with template.HTMLEscapeString for any dynamic content that may be stored in Cockroachdb and later rendered.

{{/* templates/user/show.html */}}
<div data-name="{{ .profileName | html }}"></div>
<script>
  var profileName = {{ .profileName | js }}; // js context escaping
</script>

• Audit custom template functions and ensure they do not produce raw SQL or HTML. If you register a helper that formats database output, validate and escape within the helper before returning template.HTML.

// safeFuncs limits dangerous outputs
func safeFormat(s string) template.HTML {
    // perform validation/escaping here
    return template.HTML(html.EscapeString(s))
}

• Use middleBrick’s scans to verify that endpoints involving Cockroachdb do not reflect unsanitized input in error messages or OpenAPI examples, which can become pivot points for SSTI or data exposure.