Xpath Injection in Fiber with Cockroachdb

Xpath Injection occurs when user input is concatenated into an XPath expression without proper sanitization or parameterization, leading to altered query logic or data exposure. In a Fiber application using Cockroachdb, the risk arises when XML or structured data is queried via XPath and user-controlled values are embedded directly into the expression. Cockroachdb supports XML functions and can return XML data, which may be processed in Go handlers using XPath libraries. If a developer builds an XPath string by interpolating request parameters, an attacker can manipulate the path to access unintended nodes or bypass intended filters.

Consider a Fiber endpoint that retrieves user preferences stored as XML in a Cockroachdb table. A vulnerable implementation might concatenate a user-supplied key into an XPath expression:

doc.SelectAttr("user[username='" + username + "']")

An attacker providing ' or username='admin as the username can change the predicate logic, potentially returning another user’s data or causing an error that reveals stack traces. Because Cockroachdb returns XML results, the injected XPath can affect which nodes are selected, enabling data exposure or privilege escalation within the application logic. This pattern aligns with the BOLA/IDOR and Input Validation checks in middleBrick’s 12 security checks, which flag unsafe consumption and improper authorization around user-supplied input.

Additionally, if the application uses XPath variables improperly or fails to validate input against a schema, the attack surface expands. middleBrick’s unauthenticated scan would detect such injection points by analyzing the API surface and correlating findings with the OpenAPI spec, highlighting endpoints where XML data is exposed without proper parameterization. The absence of prepared XPath expressions or strict input validation makes the combination of Fiber, Cockroachdb, and XPath susceptible to tampering, data leakage, or unexpected behavior.

To remediate Xpath Injection in Fiber when working with Cockroachdb, avoid string concatenation for XPath expressions. Use parameterized approaches or structured queries that separate data from path logic. Below are concrete code examples demonstrating secure patterns.

1. Use XPath variables with a library that supports binding

Some Go XPath libraries allow variable binding. Define a parameterized expression and supply values separately:

// Example using a hypothetical XPath library that supports variables
expr := "//user[username=$username]"
var result xml.Node
err := db.QueryRowx(context.Background(), "SELECT metadata FROM profiles WHERE id = $1", userID).Scan(&result)
// Pass variables to the XPath evaluator if supported
nodes := xpath.Select(result, expr, map[string]interface{}{"username": username})

2. Validate and restrict input before using in XPath

Enforce strict allow-lists for values that influence XPath selection. For example, if selecting by known usernames, validate against a database of permitted values:

validUsers := []string{"alice", "bob", "charlie"}
if !contains(validUsers, username) {
    c.Status(http.StatusBadRequest).JSON(map[string]string{"error": "invalid user"})
    return
}
// Proceed with a parameterized query or safe construction
query := fmt.Sprintf("//user[username='%s']", username) // Only after strict validation
nodes := root.SelectElements(query)

3. Use Cockroachdb SQL to filter before XPath processing

Leverage Cockroachdb’s SQL capabilities to narrow results before applying XPath, reducing reliance on XPath-level filtering:

rows, err := db.Queryx("SELECT xml_data FROM user_settings WHERE username = $1", username)
if err != nil || len(rows) == 0 {
    c.Status(http.StatusNotFound).JSON(map[string]string{"error": "not found"})
    return
}
var xmlData string
for rows.Next() {
    rows.Scan(&xmlData)
}
// Parse xmlData and apply minimal XPath locally for extraction
root, _ := xml.Parse(strings.NewReader(xmlData))
nameNode := root.SelectAttr("fullname")
c.JSON(map[string]string{"name": nameNode})

These approaches ensure that user input does not directly dictate XPath structure. By combining Cockroachdb’s SQL filtering with cautious local parsing, you minimize injection risks. middleBrick’s scans can verify that such mitigations are in place by checking for parameterized queries and input validation logic, supporting compliance with OWASP API Top 10 and related frameworks.