Unicode Normalization in Echo Go with Firestore

Unicode normalization inconsistencies between an HTTP framework and a database can create authorization bypasses and data exposure. In Echo Go, if route or query parameters are compared to Firestore document IDs or fields without canonical normalization, semantically equivalent strings may be treated as different values. This mismatch can allow an authenticated user to access or modify resources they should not reach, particularly in BOLA/IDOR and Property Authorization checks.

For example, a user identifier might be submitted in NFC form while Firestore stores it in NFD, or vice versa. An access control that compares the raw request value to the stored value will evaluate as false, bypassing intended restrictions. Firestore does not automatically normalize Unicode, so strings are stored exactly as written. If Echo Go does not enforce normalization before using those strings as keys or query filters, the application may unintentionally leak data or allow privilege escalation across user boundaries.

This issue is amplified when Firestore document IDs or indexed fields are derived from user input, such as email addresses or usernames. Different normalization forms can map to the same visual representation but different byte sequences, causing queries to return unintended subsets of data or fail to enforce row-level ownership. In a security scan, such inconsistencies are flagged under BOLA/IDOR and Property Authorization because the boundary between one user’s data and another’s becomes unreliable.

Additionally, input validation that does not normalize prior to rule evaluation can allow crafted sequences to bypass allowlists or regex checks. An attacker might supply composed characters that pass an allowlist check but are interpreted differently downstream when Firestore performs exact-match filtering. This can lead to Insecure Direct Object Reference (IDOR) patterns where object references are predictable across normalization variants.

middleBrick’s 12 security checks run in parallel and would surface these concerns under BOLA/IDOR and Property Authorization, highlighting where normalization gaps exist between Echo Go routing logic and Firestore storage semantics. The scanner does not assume any internal architecture; it observes that equivalent identifiers can map to different Firestore keys, indicating a risk in how data access boundaries are enforced.

To mitigate Unicode normalization issues, normalize all user-controlled strings to a consistent form before using them in Firestore document IDs, field values, or query constraints. Use a standard library to ensure deterministic behavior across requests and storage boundaries.

Below is a concrete example in Go using the Echo framework and the Firestore Go SDK. The code normalizes incoming identifiers to NFC using golang.org/x/text/unicode/norm and uses the normalized value for all Firestore operations.

import (
    "github.com/labstack/echo/v4"
    "cloud.google.com/go/firestore"
    "golang.org/x/text/unicode/norm"
    "strings"
)

func normalizeNFC(s string) string {
    return norm.String(norm.NFC, s)
}

func getUserProfile(c echo.Context) error {
    client, err := firestore.NewClient(c.Request().Context(), "your-project-id")
    if err != nil {
        return c.String(500, "failed to create client")
    }
    defer client.Close()

    userID := c.Param("userID")
    normalizedID := normalizeNFC(userID)

    docRef := client.Collection("profiles").Doc(normalizedID)
    var profile map[string]interface{}
    if err := docRef.Get(c.Request().Context(), &profile); err != nil {
        return c.String(404, "profile not found")
    }

    return c.JSON(profile)
}

func updateUserSettings(c echo.Context) error {
    client, err := firestore.NewClient(c.Request().Context(), "your-project-id")
    if err != nil {
        return c.String(500, "failed to create client")
    }
    defer client.Close()

    userID := c.Param("userID")
    normalizedID := normalizeNFC(userID)

    updates := map[string]interface{}{
        "theme": c.FormValue("theme"),
        "lang":  c.FormValue("lang"),
    }

    _, err = client.Collection("settings").Doc(normalizedID).Set(c.Request().Context(), updates, firestore.MergeAll)
    if err != nil {
        return c.String(500, "update failed")
    }

    return c.NoContent(204)
}

For queries that filter on user-supplied strings, normalize the filter value before constructing the Firestore query. This ensures that indexed fields are compared in a canonical form and reduces the risk of bypassing row-level ownership checks.

In a production deployment, you might wrap Firestore client usage in a helper that enforces normalization consistently. middleBrick’s GitHub Action can be added to your CI/CD pipeline to flag endpoints where user input flows into Firestore keys or filters without normalization, helping you fail builds before insecure patterns reach production.