Ldap Injection in Echo Go with Dynamodb

Ldap Injection occurs when user input is concatenated into an LDAP query without validation or escaping, allowing an attacker to manipulate the query structure. In an Echo Go service that uses Amazon DynamoDB as a backend identity store, this typically happens when usernames, emails, or group names retrieved from LDAP are used to query DynamoDB with unchecked string interpolation. For example, if the application performs an LDAP bind or search using input directly embedded in the filter and then uses a derived attribute (e.g., username) to fetch user metadata from DynamoDB, an attacker can inject LDAP metacharacters such as *, (, ), or " to alter query logic.

Consider an Echo Go handler that first authenticates against LDAP using a user-supplied username and then fetches additional user data from DynamoDB. If the LDAP filter is built as (&(uid=USERNAME)(objectClass=person)) where USERNAME is directly concatenated, an attacker can provide admin*)(uid=*) to turn the filter into (&(uid=admin*)(uid=*)(objectClass=person)), potentially returning multiple entries or bypassing authentication. The same input is then used as a DynamoDB key condition or filter expression. Because DynamoDB does not understand LDAP syntax, the injection surface is indirect: the vulnerability lies in how the application builds the LDAP query and maps the result to DynamoDB operations. If the application trusts the LDAP-derived identifier without further validation, malicious input can cause unintended DynamoDB operations such as reading other users’ items or triggering conditional checks that bypass authorization.

In practice, this combination amplifies risk because LDAP often runs with elevated privileges in on‑premises directories, while DynamoDB may contain sensitive profile data. An attacker who manipulates the LDAP query might coax the service into performing a DynamoDB GetItem or Query with a skewed key expression, leading to information disclosure. For instance, by injecting a wildcard in the LDAP filter, the attacker can enumerate users and then exploit the resulting usernames to probe DynamoDB for accessible resources. Because Echo Go routes and middleware can inadvertently pass raw LDAP output into DynamoDB SDK calls, the attack chain becomes feasible even when the service does not directly expose LDAP to the internet.

Remediation focuses on strict input validation, parameterized queries, and avoiding string concatenation when constructing LDAP filters and DynamoDB expressions. For LDAP, use dedicated filter building libraries that escape special characters. For DynamoDB, use the SDK’s expression builders rather than interpolating user input into condition expressions.

Below is a secure Echo Go example that demonstrates proper handling. The handler validates the username format before using it in LDAP and DynamoDB, uses parameterized LDAP filters, and employs DynamoDB ExpressionAttributeValues to prevent injection.

import (
	"github.com/labstack/echo/v4"
	"github.com/aws/aws-sdk-go-v2/service/dynamodb"
	"github.com/aws/aws-sdk-go-v2/service/dynamodb/types"
	"regexp"
)

func validateUsername(username string) bool {
	matched, _ := regexp.MatchString(`^[a-zA-Z0-9._-]{3,64}$`, username)
	return matched
}

func handleLogin(c echo.Context) error {
	username := c.FormValue("username")
	if !validateUsername(username) {
		return c.String(400, "invalid username")
	}

	// Safe LDAP filter construction (conceptual; use an LDAP library for escaping)
	ldapFilter := "(&(uid=" + ldap.EscapeFilter(username) + ")(objectClass=person))"

	// Perform LDAP bind/search here using ldapFilter

	// Safe DynamoDB Query using expression builder
	expr, exprErr := dynamodb.NewExpressionBuilder().
		WithKeyCondition("PK = :uid").
		WithExpressionAttributeValues(map[string]types.AttributeValue{
			":uid": &types.AttributeValueMemberS{Value: username},
		}).Build()
	if exprErr != nil {
		return c.String(500, "invalid expression")
	}

	input := &dynamodb.QueryInput{
		TableName:                 aws.String("Users"),
		KeyConditionExpression:    expr.KeyCondition(),
		ExpressionAttributeValues: expr.ExpressionAttributeValues(),
	}
	// Execute Query using DynamoDB client
	return c.JSON(200, map[string]string{"status": "ok"})
}

Key practices include:

• Validate and sanitize all external identifiers against a strict allowlist.
• Use ldap.EscapeFilter (or equivalent) when building LDAP filters.
• Use SDK expression builders (e.g., dynamodb.NewExpressionBuilder) and bind values via ExpressionAttributeValues instead of string concatenation.
• Avoid using raw LDAP query results as DynamoDB keys or conditionals without canonicalization.

These steps ensure that even if an attacker manages to inject LDAP metacharacters, the sanitization and parameterization prevent the injection from affecting either LDAP queries or DynamoDB operations.