Ldap Injection in Echo Go with Bearer Tokens

LDAP Injection is a server-side injection risk that occurs when an attacker can control inputs used to construct LDAP queries without proper validation or escaping. In Go services built with the Echo framework, this risk can be inadvertently exposed when authentication or authorization logic uses LDAP—such as an on‑prem Active Directory—while also relying on Bearer Tokens for API access control.

The combination creates a problematic flow: an API endpoint accepts a Bearer Token, validates or maps it (often via an LDAP bind or group lookup), and then uses unchecked user input to build LDAP search filters. If user-controlled data (e.g., a username or group filter parameter) is concatenated into the LDAP query string instead of being properly escaped, an attacker can inject malicious filter syntax. For example, a username like (uid=*))(|(objectClass=*))(&(objectClass=person) can alter the intended filter logic, potentially bypassing authentication, reading arbitrary directory entries, or triggering excessive resource consumption.

Consider an Echo handler that retrieves a username from a request query parameter and later uses it to search LDAP after Bearer Token validation:

// Unsafe: directly interpolating user input into LDAP filter
func ldapSearch(c echo.Context) error {
    token := c.Get("user").(*auth.UserContext).Username // derived from Bearer Token mapping
    username := c.QueryParam("username")
    filter := fmt.Sprintf("(uid=%s)", username)
    entries, err := ldapSearch(filter)
    if err != nil {
        return c.JSON(http.StatusInternalServerError, map[string]string{"error": "search failed"})
    }
    return c.JSON(http.StatusOK, entries)
}

Here, the Bearer Token is used to identify the requester (e.g., via a JWT mapped to an LDAP identity), but the username query parameter is directly interpolated. An attacker can supply a crafted username to manipulate the LDAP filter, potentially enumerating users or bypassing intended access logic. This is distinct from authentication bypass via the Bearer Token itself; the token may be valid, but the downstream LDAP query is compromised due to injection.

Moreover, if the service uses LDAP group membership checks to enforce authorization (e.g., requiring a specific group attribute in the directory), injection can be used to forge group membership assertions. For instance, an attacker might inject conditions that always evaluate to true, gaining access to admin functions. Because the vulnerability lies in how input shapes LDAP filters, the presence of Bearer Tokens does not mitigate the risk—it simply means the attack surface includes authenticated API calls where input handling is critical.

Remediation focuses on strict input validation and safe query construction for LDAP operations, even when requests include Bearer Tokens. Never concatenate user input into LDAP filter strings. Use parameterized filters or proper escaping provided by your LDAP library. In Echo Go, treat all user-influenced data—including values derived from token claims—as untrusted when building LDAP queries.

Below is a secure version of the earlier handler, using parameterized filters via the github.com/go-ldap/ldap/v3 package. This approach ensures user input is treated strictly as values, not as part of the filter syntax:

// Secure: parameterized filter with explicit attribute and escaped value
func ldapSearchSecure(c echo.Context) error {
    // Example Bearer Token mapping: token claims validated earlier
    _ = c.Get("user") // token-based identity, not directly used in LDAP filter

    username := c.QueryParam("username")
    if username == "" {
        return c.JSON(http.StatusBadRequest, map[string]string{"error": "username is required"})
    }

    // Use ldap.NewEscapeFilter to safely escape special characters
    escapedUsername, err := ldap.NewEscapeFilter(username)
    if err != nil {
        return c.JSON(http.StatusBadRequest, map[string]string{"error": "invalid username"})
    }

    // Parameterized approach: build filter safely
    filter := fmt.Sprintf("(uid=%s)", escapedUsername)
    // Alternatively, use ldap.NewSearchRequest for more control:
    // searchReq := ldap.NewSearchRequest(
    //     "dc=example,dc=com",
    //     ldap.ScopeWholeSubtree, ldap.NeverDerefAliases, 0, 0, false,
    //     filter,
    //     []string{"mail", "cn"},
    //     nil,
    // )

    entries, err := ldapSearch(filter)
    if err != nil {
        return c.JSON(http.StatusInternalServerError, map[string]string{"error": "search failed"})
    }
    return c.JSON(http.StatusOK, entries)
}

Additional defensive practices include:

• Validate and sanitize input against strict patterns (e.g., allow only alphanumeric and a limited set of safe characters for usernames).
• Use bind distinguished name (DN) construction with proper escaping for RDNs, leveraging functions like ldap.EscapeFilter or equivalent to neutralize special characters such as *, (, ), and \.
• Enforce least-privilege LDAP service accounts used by the service to minimize the impact of any residual injection risk.
• Log and monitor suspicious inputs (e.g., filter syntax anomalies) without exposing sensitive data in logs.

These steps ensure that Bearer Token usage for identity and LDAP operations remain independent and safe: tokens handle authentication context, while strict input handling secures directory queries.