Out Of Bounds Write in Fiber with Cockroachdb

An Out Of Bounds Write occurs when an API writes data to a memory location outside the intended allocation. In a Fiber-based service that uses CockroachDB as the primary datastore, the risk is introduced not by CockroachDB itself, but by how application code constructs and executes SQL statements, typically via string concatenation or incorrect use of placeholders. When user-controlled input is directly interpolated into dynamic SQL, an attacker can manipulate array indices, slice boundaries, or pagination parameters to craft a request that writes data to an unexpected row or column. For example, a handler that uses OFFSET or array subscripts derived from query parameters can be tricked into writing to an index that maps to an adjacent record, effectively bypassing intended isolation between tenants or user records.

Consider a multi-tenant endpoint in Fiber that updates a user profile using a tenant ID and a zero-based index provided by the client. If the index is used in a SQL UPDATE with an array slice or a calculated offset without strict bounds checking, an attacker supplying a negative or very large index can cause the database driver to generate a query that writes beyond the intended row. This can overwrite another tenant’s data or corrupt metadata. With CockroachDB, which emphasizes serializable isolation and distributed consistency, such an out-of-bounds write might not immediately surface as a crash but can lead to logical data corruption that violates row-level security assumptions. The vulnerability is exposed when input validation is limited to type checks rather than range checks, and when the application assumes the database will enforce boundaries that it actually does not.

Moreover, if the Fiber application uses dynamic table or column names constructed from user input—such as routing requests to different logical tables based on a path parameter—combined with CockroachDB’s SQL interface, an out-of-bounds write can manifest as an insertion into an unintended table or an update to a system-defined column. This is especially dangerous when combined with features like computed columns or indexes that rely on expression evaluation. The database will accept and persist the malformed write, and the application may return a success response, masking the integrity compromise. Because CockroachDB does not inherently validate application-level index semantics, the responsibility falls on the service to enforce correct bounds before constructing queries.

In practice, this class of flaw often aligns with OWASP API Top 10 categories such as Broken Object Level Authorization (BOLA) and Improper Input Validation. An attacker may chain an out-of-bounds write with other techniques to escalate privileges or exfiltrate data, especially if the same handler lacks proper authentication or tenant isolation. Since middleBrick tests for BOLA/IDOR and Input Validation in parallel, it can identify risky patterns like unchecked numeric parameters used in SQL statements, even when the endpoint appears to be unauthenticated. Recognizing how the application maps HTTP parameters to database operations is key to understanding the attack surface in this specific Fiber and CockroachDB stack.

To prevent Out Of Bounds Write in Fiber when interacting with CockroachDB, enforce strict validation and use parameterized queries with explicit bounds. Never directly concatenate user input into SQL strings, and avoid using raw indexes or offsets without verifying they fall within acceptable ranges. The following examples demonstrate secure patterns using the pgx driver, which is compatible with CockroachDB.

1. Validate numeric indices and offsets

Ensure any user-supplied index or offset is non-negative and within a known limit before using it in a query.

package main

import (
    "net/http"
    "strconv"

    "github.com/gofiber/fiber/v2"
    "github.com/jackc/pgx/v5/pgxpool"
)

func updateUserProfile(pool *pgxpool.Pool) fiber.Handler {
    return func(c *fiber.Ctx) error {
        tenantID := c.Params("tenant")
        indexStr := c.Query()("index")
        index, err := strconv.Atoi(indexStr)
        if err != nil || index < 0 || index >= 1000 {
            return c.Status(http.StatusBadRequest).JSON(fiber.Map{"error": "invalid index"})
        }

        var updateData string
        // Use a placeholder for data, index is validated in Go
        err = pool.QueryRow(c.Context(),
            "UPDATE tenant_profiles SET data = $1 WHERE tenant_id = $2 AND profile_index = $3",
            "new_value", tenantID, index).Scan(&updateData)
        if err != nil {
            return c.Status(http.StatusInternalServerError).JSON(fiber.Map{"error": err.Error()})
        }
        return c.JSON(fiber.Map{"status": "ok"})
    }
}

2. Use parameterized queries with placeholders for dynamic SQL

When table or column names must be dynamic, use an allowlist to map identifiers rather than interpolating directly.

func safeWrite(c *fiber.Ctx, pool *pgxpool.Pool, table string) error {
    allowedTables := map[string]bool{
        "users_v1": true,
        "users_v2": true,
    }
    if !allowedTables[table] {
        return c.Status(http.StatusBadRequest).JSON(fiber.Map{"error": "invalid table"})
    }

    query := "INSERT INTO " + table + " (tenant_id, payload) VALUES ($1, $2)"
    _, err := pool.Exec(c.Context(), query, c.Locals("tenant"), c.Body())
    if err != nil {
        return c.Status(http.StatusInternalServerError).JSON(fiber.Map{"error": err.Error()})
    }
    return nil
}

3. Apply row-level checks before writing

Even with validated input, confirm that the target row belongs to the requesting tenant using a SELECT...FOR UPDATE pattern to prevent race conditions.

func conditionalUpdate(pool *pgxpool.Pool, tenantID string, index int) error {
    tx, err := pool.Begin(context.Background())
    if err != nil {
        return err
    }
    defer tx.Rollback(context.Background())

    var owner string
    err = tx.QueryRow(context.Background(),
        "SELECT tenant_id FROM tenant_profiles WHERE profile_index = $1 FOR UPDATE", index).Scan(&owner)
    if err != nil {
        return err
    }
    if owner != tenantID {
        return errors.New("tenant mismatch")
    }

    _, err = tx.Exec(context.Background(),
        "UPDATE tenant_profiles SET payload = $1 WHERE profile_index = $2", "secure_data", index)
    if err != nil {
        return err
    }
    return tx.Commit(context.Background())
}

These approaches align with middleBrick’s checks for BOLA/IDOR and Input Validation, helping ensure that endpoints do not expose unbounded memory operations. By combining strict input ranges, allowlist-based identifier handling, and transactional consistency checks, you reduce the risk of out-of-bounds writes while maintaining compatibility with CockroachDB’s distributed model.