Ldap Injection in Buffalo with Bearer Tokens

Ldap Injection occurs when an attacker is able to manipulate LDAP query construction, typically by injecting malicious input into filter expressions. In the Buffalo web framework for Go, this often happens when developer code builds LDAP filter strings using unchecked user input, for example concatenating form values into filter templates. The presence of Bearer Tokens does not prevent Ldap Injection; it may simply shifts the trust boundary. If an endpoint accepts a Bearer Token and uses claims (such as a username or email) to dynamically build LDAP filters, an attacker who supplies a crafted token or manipulates the Authorization header can inject characters like *, (, ), or " into the resulting filter. This can bypass authentication, cause excessive queries, or expose directory data.

Consider a Buffalo endpoint that retrieves a user profile and uses a token’s preferred_username claim to search an LDAP directory:

// WARNING: illustrative vulnerable pattern
func ProfileHandler(c buffalo.Context) error {
    tokenString := c.Request().Header.Get("Authorization")
    if tokenString == "" {
        return c.Error(401, errors.New("authorization header required"))
    }
    // naive parsing for illustration only
    parts := strings.Split(tokenString, " ")
    if len(parts) != 2 || parts[0] != "Bearer" {
        return c.Error(400, errors.New("invalid authorization format"))
    }
    claimValue := parts[1] // simulate extracting a claim value used in LDAP filter
    filter := fmt.Sprintf("(&(objectClass=person)(mail=%s))", claimValue)
    entries, err := ldapSearch(filter)
    // ... handle entries and response
}

If claimValue is controlled by an attacker (e.g., via a modified token or a compromised identity provider), they can inject LDAP metacharacters. For instance, providing admin*)(objectClass=person) alters the filter to (&(objectClass=person)(mail=admin*)(objectClass=person)), which may match unintended entries or bypass intended access controls. Buffalo’s convention of binding handlers to routes does not inherently validate or sanitize inputs derived from authentication tokens, so the framework does not protect against this class of injection. Moreover, misconfigured logging or error messages can inadvertently disclose filter contents or directory structure, aiding further exploitation.

It is important to note that middleBrick detects such patterns by correlating OpenAPI/Swagger specifications with runtime behavior, including authentication schemes like Bearer Tokens. The scanner does not modify application logic; it identifies places where user-influenced data is used in LDAP filter construction and highlights related findings such as BOLA/IDOR or Unsafe Consumption. The scanner also exercises LLM/AI Security checks, which include active prompt injection tests and system prompt leakage detection, but these are focused on LLM endpoints and do not mitigate LDAP injection risks in API endpoints using tokens.

Remediation centers on never directly interpolating user or token-derived values into LDAP filters. Instead, use parameterized LDAP queries or properly escape special filter characters. In Buffalo, this means validating and sanitizing any data used to construct filters, and favoring library functions that handle escaping. Below are two concrete, secure patterns for Buffalo handlers using Bearer Tokens.

1. Use an LDAP library that supports parameterized filters

Many Go LDAP libraries allow building filters with placeholders and passing values separately, avoiding string concatenation. For example, using a hypothetical LDAP client that supports parameterized filtering:

// Secure pattern with parameterized filter
func ProfileHandler(c buffalo.Context) error {
    tokenString := c.Request().Header.Get("Authorization")
    if tokenString == "" {
        return c.Error(401, errors.New("authorization header required"))
    }
    parts := strings.Split(tokenString, " ")
    if len(parts) != 2 || parts[0] != "Bearer" {
        return c.Error(400, errors.New("invalid authorization format"))
    }
    claimValue := parts[1]
    // Use a library function that builds a filter safely
    filter, args := ldap.Filter("mail", claimValue)
    entries, err := ldapSearch(filter, args...)
    if err != nil {
        return c.Error(500, errors.New("search failed"))
    }
    // ... process entries
}

If your LDAP client does not provide a built-in filter builder, manually escape metacharacters according to RFC 4515. In Buffalo, implement a small helper and apply it consistently:

2. Escape metacharacters manually and validate input format

// escapeLDAPFilter escapes reserved characters for RFC 4515
func escapeLDAPFilter(value string) string {
    // Replace according to RFC 4515: * -> \2a, ( -> \28, ) -> \29, \ -> \5c, null -> \00
    var b strings.Builder
    for _, r := range value {
        switch r {
        case '*':
            b.WriteString(`\2a`)
        case '(': 
            b.WriteString(`\28`)
        case ')':
            b.WriteString(`\29`)
        case '\\':
            b.WriteString(`\5c`)
        case '\x00':
            b.WriteString(`\00`)
        default:
            b.WriteRune(r)
        }
    }
    return b.String()
}

// Secure handler with escaping and length validation
func ProfileHandler(c buffalo.Context) error {
    tokenString := c.Request().Header.Get("Authorization")
    if tokenString == "" {
        return c.Error(401, errors.New("authorization header required"))
    }
    parts := strings.Split(tokenString, " ")
    if len(parts) != 2 || parts[0] != "Bearer" {
        return c.Error(400, errors.New("invalid authorization format"))
    }
    claimValue := parts[1]
    if len(claimValue) > 254 {
        return c.Error(400, errors.New("invalid input length"))
    }
    safeValue := escapeLDAPFilter(claimValue)
    filter := fmt.Sprintf("(&(objectClass=person)(mail=%s))", safeValue)
    entries, err := ldapSearch(filter)
    if err != nil {
        return c.Error(500, errors.New("search failed"))
    }
    // ... process entries
}

Additionally, prefer static or admin-defined bind credentials for LDAP connections rather than injecting directory search bases from tokens. In CI/CD, the middleBrick CLI can be used to scan endpoints and surface insecure LDAP usage; integrating the GitHub Action helps fail builds when risky patterns are detected. The Dashboard can track scores over time to ensure that changes do not reintroduce injection risks.