Ldap Injection in Gin with Basic Auth

Ldap Injection occurs when an attacker can manipulate LDAP query construction through untrusted input. In a Gin service that uses HTTP Basic Auth, the combination of direct credential parsing and dynamic LDAP queries can expose injection risks if the server does not strictly validate and escape incoming credentials before using them in directory searches.

Consider a Gin handler that extracts the username and password from the Basic Auth header and uses them to build an LDAP filter without sanitization:

// WARNING: vulnerable example
username := req.Header.Get("Authorization")
// naive extraction for illustration only
searchFilter := fmt.Sprintf("(&(objectClass=user)(sAMAccountName=%s))", username)
searchRequest := ldap.NewSearchRequest(
    "dc=example,dc=com",
    ldap.ScopeWholeSubtree, ldap.NeverDerefAliases, 0, 0, false,
    searchFilter,
    []string{"dn"},
    nil,
)

If the username is attacker-controlled (e.g., user)(objectClass=organizationalPerson)(objectClass=user)(cn=*), the resulting filter becomes:

(&(objectClass=user)(sAMAccountName=user)(objectClass=organizationalPerson)(objectClass=user)(cn=*))

This can bypass intended scope filters, return unintended entries, or disclose directory information. An attacker may achieve information disclosure or bypass authentication logic depending on how the application interprets the LDAP results. middleBrick will flag this as an Input Validation and Authentication finding, noting that unescaped input used in directory queries expands the attack surface.

Note that Basic Auth transmits credentials in base64 (not encryption), so transport security (TLS) is required in any case. However, the injection risk here is about how the extracted credentials are used server-side, not about transport weaknesses. Even with TLS, unsanitized credentials used to construct LDAP filters enable injection patterns similar to SQL injection in directory services.

middleBrick’s checks include Input Validation and Authentication among its 12 parallel security checks. It does not fix the issue but highlights the risky pattern and provides remediation guidance, such as avoiding string interpolation for filters and using parameterized LDAP APIs.

Remediation focuses on strict input validation, avoiding dynamic filter assembly, and using safe LDAP client APIs that separate filter structure from values. Never concatenate raw credentials into LDAP search strings.

First, enforce strong credential validation before using them in directory operations. For example, restrict usernames to a safe character set and length:

// Validate username format (alphanumeric and limited symbols)
import "regexp"
var safeUser = regexp.MustCompile(`^[a-zA-Z0-9._-]{1,64}$`)

auth := req.Header.Get("Authorization")
// parse Basic auth safely; in production use a well-maintained helper
username, password, ok := parseBasicAuth(auth) // implement or use a library
if !ok || !safeUser.MatchString(username) {
    http.Error(resp, "invalid credentials", http.StatusUnauthorized)
    return
}

Second, use parameterized or escaped queries. If your LDAP library supports escaping, apply it to each attribute value. For instance, with go-ldap:

import "github.com/go-ldap/ldap/v3"

username = ldap.EscapeFilter(username)
password = ldap.EscapeFilter(password)
searchFilter := fmt.Sprintf("(&(objectClass=user)(sAMAccountName=%s))", username)
searchRequest := ldap.NewSearchRequest(
    "dc=example,dc=com",
    ldap.ScopeWholeSubtree, ldap.NeverDerefAliases, 0, 0, false,
    searchFilter,
    []string{"dn"},
    nil,
)

Third, prefer bind-based authentication over searching with user input when possible. Attempt a direct bind using the provided credentials; this avoids constructing filters from user input entirely:

conn, err := ldap.Dial("tcp", "ldap.example.com:389")
if err != nil {
    http.Error(resp, "service error", http.StatusInternalServerError)
    return
}
defer conn.Close()

err = conn.Bind(username, password)
if err != nil {
    http.Error(resp, "invalid credentials", http.StatusUnauthorized)
    return
}
// proceed with authorized operations

Using a bind flow reduces the need to build search filters from raw credentials and aligns with least-privilege practices. Combine this with transport encryption and, where required, middleware that limits authentication attempts to mitigate brute force risks.

middleBrick’s scans can surface these patterns by correlating Authentication and Input Validation findings. The Pro plan can integrate these checks into CI/CD pipelines, so builds fail if risky credential handling is detected in your Gin routes.