Ldap Injection in Echo Go with Hmac Signatures

Ldap Injection occurs when user input is directly concatenated into LDAP queries without validation or escaping. In an Echo Go service that uses Hmac Signatures for request authentication, the vulnerability arises if an attacker can inject LDAP filter syntax into a parameter that is later used in an LDAP query, even when the request is protected by Hmac Signatures.

Hmac Signatures are typically used to ensure request integrity and authenticity. The client computes an HMAC over selected parts of the request (e.g., selected headers and the body) using a shared secret and sends it in an Authorization header. The server recomputes the HMAC and compares it to the client-supplied value. If the comparison is performed incorrectly (e.g., using a non-constant-time compare) or if the server trusts data that should have been validated before being used in LDAP, the HMAC check can pass while the underlying data is malicious.

Consider an authentication flow where the client provides a username and a timestamp, the server validates the Hmac Signature, and then uses the username to construct an LDAP filter such as (&(uid={username})(objectClass=person)). If the username is not sanitized, an attacker can supply a value like admin)(uid=*)(objectClass=user). The resulting LDAP filter becomes (&(uid=admin)(uid=*)(objectClass=user)(objectClass=person)), which may bypass intended access controls and return unintended entries. This happens despite the presence of Hmac Signatures because the signature does not protect the semantics of the data; it only binds the client to the raw values they supplied.

An attacker might also target endpoints that accept JSON payloads and then forward user-controlled fields into LDAP queries. For example, an API endpoint could accept { "username": "...", "filter": "..." }, validate the Hmac over the JSON body, and then construct an LDAP query using the filter field directly. If the filter field is attacker-controlled and used verbatim, it can contain LDAP metacharacters such as *, (, ), and &, enabling injection. The Hmac Signature ensures the payload hasn’t been altered in transit, but it does not prevent the server from misusing trusted input.

Real-world impact can resemble CVE-like patterns where authenticated attackers escalate privileges or access other users’ data by abusing improper input handling. Even with Hmac Signatures providing integrity, the unchecked use of user input in LDAP filters exposes the application to classic injection classes mapped to OWASP API Top 10 and can lead to unauthorized data retrieval or authentication bypass.

Remediation focuses on validating and sanitizing all user-controlled data before it is used in LDAP queries, independent of the Hmac Signature verification. Do not rely on the Hmac to protect against injection; treat it as a separate integrity check.

Use parameterized LDAP queries or an LDAP library that supports escaping. In Go, the github.com/go-ldap/ldap/v3 package provides functions to build filters safely. Avoid string concatenation for filter construction.

Example of vulnerable code in Echo Go:

import (
    "github.com/labstack/echo/v4"
    "github.com/go-ldap/ldap/v3"
)

func unsafeHandler(c echo.Context) error {
    username := c.FormValue("username")
    // Vulnerable: direct string concatenation into LDAP filter
    filter := fmt.Sprintf("(&(uid=%s)(objectClass=person))", username)
    l, err := ldap.ParseFilter(filter)
    if err != nil {
        return c.String(http.StatusBadRequest, "invalid filter")
    }
    // ... use l with LDAP connection
    return c.JSON(http.StatusOK, map[string]string{"ok": "true"})
}

Example of secure remediation using parameterized filter building:

import (
    "github.com/labstack/echo/v4"
    "github.com/go-ldap/ldap/v3"
)

func safeHandler(c echo.Context) error {
    username := c.FormValue("username")
    // Validate input: allow only safe characters for uid
    if !isValidUsername(username) {
        return c.String(http.StatusBadRequest, "invalid username")
    }
    // Safe: construct filter using ldap.Filter{} to avoid injection
    filter := ldap.NewAndFilter().
        AddFilter(ldap.NewPresenceFilter("objectClass", "person")).
        AddFilter(ldap.NewEqualityFilter("uid", username))
    l, err := ldap.ParseFilter(filter.String())
    if err != nil {
        return c.String(http.StatusInternalServerError, "server error")
    }
    // ... use l with LDAP connection
    return c.JSON(http.StatusOK, map[string]string{"ok": "true"})
}

func isValidUsername(value string) bool {
    // Allow alphanumeric, underscore, hyphen; reject special LDAP characters
    matched, _ := regexp.MatchString(`^[A-Za-z0-9_-]+$`, value)
    return matched
}

If you must accept freeform filter components, encode or escape each component using the LDAP library’s escaping functions. For example, use ldap.EscapeFilter(username, "", ldap.EscapeFilterModeGeneral) to escape special characters. Also enforce strict schema validation and avoid using user input to dynamically select object classes or attributes.

When Hmac Signatures are used to bind a request to a specific user or intent, ensure that the server-side validation of the Hmac does not skip additional context checks. For instance, confirm that the username in the Hmac payload matches the username used in the LDAP query, and apply the same allowlist validation before constructing filters.