Ldap Injection in Fiber with Api Keys

Ldap Injection occurs when an attacker can manipulate LDAP query construction by injecting malicious input. In a Fiber application that uses API keys for access control, the vulnerability arises when API key validation is performed against an LDAP directory and user-controlled data is concatenated into the LDAP filter without sanitization or parameterized queries.

Consider a scenario where a Fiber handler authenticates requests by binding to an LDAP server using an API key passed in an HTTP header. If the handler builds the LDAP filter by string interpolation, an attacker can supply a crafted API key such as (uid=* or )(objectClass=*) to alter the filter logic. This can lead to authentication bypass, unauthorized account enumeration, or extraction of directory data. For example, an insecure implementation might concatenate the API key directly into the filter:

filter := fmt.Sprintf("(uid=%s)", apiKey)

An attacker providing apiKey=*)(objectClass=person) could cause the filter to become (uid=*)(objectClass=person)), potentially returning multiple entries or bypassing intended constraints. Because API keys are often treated as highly trusted, developers may skip input validation, increasing the risk of injection. Additionally, if the LDAP query is used for authorization checks (e.g., group membership), manipulated results can lead to privilege escalation.

The 12 security checks in middleBrick exercise this attack surface in black-box mode, including Input Validation and Authentication. When scanning a Fiber endpoint that accepts API keys and interacts with LDAP, the scanner tests whether the API key is reflected in LDAP responses or used in dynamically constructed filters. Findings may map to the OWASP API Top 10 category '2023-A1: Broken Object Level Authorization' and related patterns such as BOLA/IDOR when directory traversal or enumeration is possible.

To secure a Fiber application that uses API keys with LDAP, avoid string concatenation when building LDAP filters. Use parameterized APIs or prepared search templates that treat the API key as a literal value, not as part of the filter syntax. Always validate and sanitize input, enforce strict allowlists for API key formats, and avoid exposing detailed error messages that aid attackers.

Below are concrete code examples in Go using the Fiber framework and a typical LDAP library.

Secure API key handling and LDAP search

Use a whitelist of allowed characters for API keys and treat the key as a bound parameter. For instance, if your directory uses uid attributes, perform an exact-match lookup rather than a substring search when possible:

// Validate API key format (alphanumeric and underscores)
if !regexp.MustCompile(`^[A-Za-z0-9_]{16}$`).MatchString(apiKey) {
    c.Status(http.StatusBadRequest).JSON(fiber.Map{"error": "invalid key"})
    return
}
// Use a client search with a filter that treats the key as a value
searchRequest := ldap.NewSearchRequest(
    "ou=users,dc=example,dc=com",
    ldap.ScopeWholeSubtree, ldap.NeverDerefAliases, 0, 0, false,
    fmt.Sprintf("(uid=%s)", ldap.EscapeFilter(apiKey)),
    []string{"dn", "uid"},
    nil,
)
result, err := conn.Search(searchRequest)
if err != nil || len(result.Entries) != 1 {
    c.Status(http.StatusUnauthorized).JSON(fiber.Map{"error": "invalid credentials"})
    return
}
dn := result.Entries[0].DN
bindErr := conn.Bind(dn, password) // password obtained securely, e.g., from a vault
if bindErr != nil {
    c.Status(http.StatusUnauthorized).JSON(fiber.Map{"error": "invalid credentials"})
    return
}

If your LDAP library supports parameterized filters, prefer that approach to further reduce risk:

// Hypothetical parameterized API; adjust to your LDAP client's actual API
searchRequest := ldap.NewSearchRequest(
    "ou=users,dc=example,dc=com",
    ldap.ScopeWholeSubtree, ldap.NeverDerefAliases, 0, 0, false,
    "(uid=?)",
    []string{"uid"},
    []interface{}{apiKey},
)
result, err := conn.Search(searchRequest)

Additionally, rotate API keys regularly, store them securely, and apply rate limiting in Fiber to mitigate credential stuffing. middleBrick’s CLI can be used to verify that your endpoints do not reflect API keys in error messages or directory responses:

middlebrick scan https://api.example.com/v1/health

For automated checks in development, the GitHub Action can fail builds if a scan detects findings related to authentication or input validation. The MCP Server enables scanning API definitions directly from your AI coding assistant, helping catch LDAP-related issues before deployment.