Format String in Echo Go with Cockroachdb

A format string vulnerability occurs when user-controlled input is passed directly into functions that format output, such as fmt.Sprintf or fmt.Printf, without explicit format specifiers. In an Echo Go application that interacts with Cockroachdb, this typically arises when constructing SQL queries or log messages using unchecked request parameters. For example, if a developer builds a query using string formatting with user input, an attacker can supply format verbs like %s, %x, or %n to read stack memory or cause writes, leading to information disclosure or unexpected behavior.

When this pattern is combined with Cockroachdb, the risk surface expands because the database driver may propagate or log these malformed queries. If the application uses db.Query with a format string built from request parameters, an attacker can inject format specifiers that affect how the query is parsed or logged by the database layer. Although Cockroachdb itself does not interpret Go format verbs, the surrounding Go runtime and logging infrastructure may expose sensitive data or crash under malformed format operations. This becomes particularly dangerous in unauthenticated scan scenarios where endpoints accept query parameters that are directly interpolated into SQL strings.

Consider an endpoint that retrieves a user record by ID but uses formatted logging:

import (
    "fmt"
    "net/http"
    "github.com/labstack/echo/v4"
    "github.com/lib/pq"
)

func getUser(c echo.Context) error {
    userID := c.QueryParam("id")
    query := fmt.Sprintf("SELECT username, email FROM users WHERE id = %s", userID)
    c.Logger().Infof(query) // Unsafe: userID may contain format verbs
    rows, err := db.Query(query)
    if err != nil {
        return err
    }
    defer rows.Close()
    // process rows
    return c.JSON(http.StatusOK, "ok")
}

In this scenario, if userID is set to %s%s%s%s%s, the log output may expand and reveal stack contents or internal paths. While Cockroachdb will still receive a syntactically valid query, the surrounding Go process may behave unpredictably due to format string misuse. MiddleBrick’s LLM/AI Security checks and unauthenticated scan capabilities can detect such patterns by analyzing the unauthenticated attack surface and flagging risky code paths that involve direct string interpolation before database interaction.

Additionally, if the application uses structured logging or metrics that include user input before sending events to Cockroachdb, format strings in those systems can cause similar issues. The database driver’s logging or telemetry may inadvertently expose these malformed calls during error reporting. This highlights the importance of validating and sanitizing all inputs before they are used in any formatting operation, especially when those operations interface with external systems like Cockroachdb.

Remediation focuses on avoiding string interpolation for SQL construction and ensuring that user input is never directly embedded into format strings. Use parameterized queries with placeholders, which separate SQL logic from data entirely. This prevents format verbs from being interpreted as part of the query structure and eliminates the risk of format string attacks at the application level.

Below is a secure version of the previous example using placeholders:

import (
    "net/http"
    "github.com/labstack/echo/v4"
    "database/sql"
)

func getUserSecure(c echo.Context) error {
    userID := c.QueryParam("id")
    var username, email string
    // Use parameterized query to prevent format string issues
    err := db.QueryRow("SELECT username, email FROM users WHERE id = $1", userID).Scan(&username, &email)
    if err != nil {
        if err == sql.ErrNoRows {
            return c.JSON(http.StatusNotFound, map[string]string{"error": "user not found"})
        }
        return c.JSON(http.StatusInternalServerError, map[string]string{"error": "server error"})
    }
    return c.JSON(http.StatusOK, map[string]string{"username": username, "email": email})
}

In this corrected implementation, $1 is a placeholder bound to the Cockroachdb driver, ensuring that userID is always treated as a literal value. No formatting occurs in Go code, so format string attacks are impossible. This pattern works consistently across SQL drivers and aligns with best practices for database interaction in networked applications.

For logging purposes, avoid passing user input directly to log format strings. Instead, use structured logging with explicit fields:

import (
    "github.com/sirupsen/logrus"
)

func logUserAccess(userID string) {
    logrus.WithField("user_id", userID).Info("user lookup attempted")
}

By using field-based logging, you prevent accidental interpretation of user input as format verbs. MiddleBrick’s dashboard and CLI can help identify remaining instances of risky formatting by scanning unauthenticated endpoints and flagging patterns that involve string concatenation before database calls or logging. Upgrading to the Pro plan enables continuous monitoring of these issues across tracked APIs, with alerts triggered when new risky patterns appear in updated code or configurations.