Format String in Buffalo with Cockroachdb

A format string vulnerability occurs when user-controlled input is passed directly into a formatted output function without proper sanitization. In the Buffalo web framework, this typically arises when constructing database queries or logging messages using Go’s fmt family of functions (e.g., fmt.Sprintf, fmt.Printf) with unchecked input. When combined with CockroachDB, a PostgreSQL-compatible distributed database, the risk is compounded due to CockroachDB’s use of PostgreSQL wire protocol and its handling of placeholders.

In Buffalo, developers often build SQL queries dynamically using string concatenation or interpolation. For example, consider a handler that constructs a query using user input for a table or column name:

app.Get("/users/{id}", func(c buffalo.Context) error {
    id := c.Param("id")
    query := fmt.Sprintf("SELECT * FROM users WHERE id = %s", id)
    var users []models.User
    if err := conn.Raw(query).Select(&users); err != nil {
        return c.Error(500, err)
    }
    return c.Render(200, r.H{"users": users})
})

If id contains format specifiers such as %s, %x, or %v, fmt.Sprintf will interpret them, potentially causing unexpected behavior, information disclosure, or even arbitrary code execution depending on the input. While CockroachDB itself does not directly execute format strings, the database driver (usually lib/pq or pgx) passes the final string as a query argument. However, if the format string is used in logging, error messages, or debug output before reaching CockroachDB, an attacker can inject malicious format specifiers to read stack memory, disclose sensitive data, or cause a denial of service.

The LLM/AI Security checks in middleBrick specifically detect such patterns by scanning for improper use of formatting functions with external input. Since Buffalo applications often rely on rapid prototyping, developers might inadvertently pass request parameters directly into formatted strings. middleBrick’s scan would flag this as a high-severity finding under Input Validation and Data Exposure checks, highlighting the need for strict input validation and the use of parameterized queries.

Moreover, because CockroachDB supports advanced SQL features like JSONB and arrays, attackers might attempt to exploit format strings to inject complex expressions or escape query contexts. For instance, a payload like 1; SELECT * FROM secrets could be misinterpreted if not properly sanitized, especially when combined with format specifiers that alter string interpretation. middleBrick’s cross-referencing of OpenAPI specs with runtime behavior helps identify such mismatches in expected input types versus actual usage.

Remediation focuses on eliminating direct string interpolation and enforcing strict parameterization. In Buffalo, prefer using the ORM’s built-in query methods or parameterized SQL statements instead of constructing queries with fmt.Sprintf. Below is a secure alternative to the earlier vulnerable example:

app.Get("/users/{id}", func(c buffalo.Context) error {
    var user models.User
    if err := conn.Where("id = ?", c.Param("id")).First(&user); err != nil {
        return c.Error(500, err)
    }
    return c.Render(200, r.H{"user": user})
})

This approach ensures that the input is treated strictly as a value, not as part of the SQL command structure. The placeholder ? is replaced safely by the database driver, preventing format string injection.

For cases where raw SQL is necessary, use ? placeholders with conn.Exec or conn.Select:

var users []models.User
if err := conn.Select(&users, "SELECT * FROM users WHERE id = $1", c.Param("id")); err != nil {
    return c.Error(500, err)
}

Note that CockroachDB uses $1, $2 style placeholders for positional parameters in raw queries, aligning with PostgreSQL conventions. Avoid concatenating user input into the query string, even for non-format-related purposes such as dynamic table names. If dynamic table names are required, validate them against a strict allowlist before use:

allowedTables := map[string]bool{"users": true, "products": true}
table := c.Param("table")
if !allowedTables[table] {
    return c.Error(400, errors.New("invalid table name"))
}
query := fmt.Sprintf("SELECT * FROM %s", table) // Still risky; prefer static mappings

Even with validation, prefer mapping table names to predefined queries to avoid any format string risk. Additionally, ensure all logging within Buffalo applications uses structured logging with parameterized messages, avoiding direct inclusion of user input in log formats. middleBrick’s scan can verify that no format specifiers appear in logging statements by analyzing source patterns and runtime outputs.