Ldap Injection in Chi with Dynamodb

Ldap Injection in a Chi application that uses Dynamodb as a backend identity store occurs when user-controlled input is concatenated into LDAP filter strings without proper escaping or validation. Chi is a lightweight routing library for Common Lisp, and when it passes query parameters such as user_id or search directly to an LDAP client that ultimately queries Dynamodb-stored directory data, it can allow an attacker to manipulate the filter logic.

For example, an endpoint /search might build an LDAP filter like (&(objectClass=person)(cn=*) by interpolating a parameter. If the parameter contains LDAP metacharacters such as *, (, ), or \, an attacker can change the filter semantics. A payload like )*(objectClass=*) can turn a restrictive filter into one that returns all entries, exposing sensitive identity attributes stored in Dynamodb-backed directory records.

Even though Dynamodb does not interpret LDAP syntax, the vulnerability arises at the application layer: Chi constructs LDAP queries using raw input, and those queries reference identities whose attribute values are stored in Dynamodb. An attacker can probe for usernames, group memberships, or administrative flags by injecting filter fragments that cause excessive or unintended results. Because the scan includes Input Validation and Authentication checks, middleBrick flags such flows as high risk when untrusted input influences LDAP filter construction, regardless of the underlying identity database.

Real-world attack patterns mirror classic LDAP Injection techniques (CWE-90), such as using (&(objectClass=person)(cn=admin)) to test for privileged accounts. The presence of Dynamodb as a persistence layer does not mitigate the injection; it simply means that leaked directory data may include Dynamodb-recorded attributes like roles or tokens. MiddleBrick’s LLM/AI Security checks also look for prompt injection parallels where similar injection logic could be repurposed against AI-facing endpoints that rely on the same identity model.

Compliance mappings are relevant here: findings align with OWASP API Top 10 Broken Object Level Authorization and Injection, and SOC2 controls around identity access. Because the scan is unauthenticated and runtime-based, middleBrick can detect whether LDAP filters constructed by Chi are susceptible to injection using only the public endpoint, then report the issue with severity and remediation guidance rather than attempting to fix or block traffic.

To remediate Ldap Injection in Chi when using Dynamodb, ensure that all user input used to build LDAP filters is either not used for LDAP queries or is rigorously sanitized. The safest approach is to avoid building LDAP filters from raw HTTP parameters entirely; instead, map validated identifiers to internal representations that never reach the LDAP layer.

If LDAP queries are necessary, use a library that provides proper escaping for LDAP filters. In Common Lisp, you can preprocess strings by escaping special characters according to RFC 4515. Below is a concrete example using a hypothetical LDAP utility that escapes input before concatenation:

(defun escape-ldap-filter (input)
  (replace-regexp-in-string
    "[\\*()\\x00-\\x1F\\x7F]"
    (lambda (match)
      (format nil "\\~2,'0X" (char-code (char match 0))))
    input))

(defun build-safe-ldap-filter (base-cn)
  (let ((safe-cn (escape-ldap-filter base-cn)))
    (format nil "(&(objectClass=person)(cn=~a))" safe-cn)))

In your Chi routes, validate and transform the parameter before using it:

(define-route app "/search" (request)
  (let* ((params (qs:parse (request-query request)))
         (raw-cn (gethash "cn" params))
         (safe-filter (when raw-cn (build-safe-ldap-filter raw-cn))))
    (if safe-filter
        (let ((results (ldap-query Dynamodb-connector (build-safe-ldap-filter raw-cn))))
          (response 200 (json:encode-json-to-string results)))
        (response 400 ("Invalid or missing search parameter")))))

Additionally, enforce strict allowlists for acceptable characters in identifiers (e.g., alphanumeric and hyphen) and prefer indirect references such as a mapping table stored in Dynamodb that links short keys to full directory entries. This way, Chi only passes validated keys to backend services, and the LDAP layer never receives user-controlled strings. middleBrick’s Property Authorization and Input Validation checks will then confirm that the endpoints no longer reflect tainted data into LDAP construction, lowering the security risk score.

For continuous protection, use the middleBrick CLI to scan from terminal with middlebrick scan <url> and integrate the GitHub Action to fail builds if insecure patterns persist. The MCP Server also allows scanning APIs directly from your AI coding assistant, helping catch injection risks earlier in development.