Ldap Injection in Chi with Jwt Tokens

Ldap Injection is a server-side injection risk that occurs when an attacker can control input used to construct an LDAP query without proper validation or escaping. In the Go ecosystem, the Chi router is commonly used to build HTTP services that may integrate with LDAP for authentication or group lookups. When JWTs are used for client authentication, the token itself is typically trusted as a cryptographically signed payload; however, the application may still combine claims from the JWT (such as username or group membership) with LDAP query parameters. If these values are concatenated into LDAP filter strings without escaping, an attacker who can influence the JWT claim (for example via a compromised issuer or a token with maliciously crafted attributes) can inject LDAP filter syntax such as (|(uid=*)(objectClass=*)) or append trailing wildcards and control characters.

Consider a Chi handler that retrieves the uid claim from a JWT and uses it to search an LDAP directory for user details. A vulnerable pattern might look like this in Go:

import (
	"github.com/go-chi/chi/v5"
	"gopkg.in/ldap.v3"
)

func userHandler(ldapConn *ldap.Conn) http.HandlerFunc {
	return func(w http.ResponseWriter, r *http.Request) {
		// Assume JWT claims have been validated and uid is extracted
		uid := chi.URLParam(r, "uid")
		filter := "(uid=" + uid + ")"
		searchReq := ldap.NewSearchRequest(
			"dc=example,dc=com",
			ldap.ScopeWholeSubtree, ldap.NeverDerefAliases, 0, 0, false,
			filter,
			[]string{"cn", "mail"},
			nil,
		)
		// Perform search and handle response...
	}
}

In this example, the uid derived from the URL path (or from a trusted JWT claim) is directly concatenated into the LDAP filter. An attacker who can influence the JWT — for instance, if the application does not strictly validate the issuer or if the token includes user-supplied attributes — could set uid to a value like admin)(uid=*)(objectClass=*). This would produce the filter (uid=admin)(uid=*)(objectClass=*)), potentially bypassing intended access controls and returning sensitive entries. Even when JWTs are validated using a robust library, the risk arises if the application treats claims as safe for direct LDAP interpolation rather than treating them as untrusted input.

Additionally, JWTs may contain groups or roles that the application uses to build dynamic LDAP filters for authorization checks. If group membership values are inserted without escaping, attackers who can manipulate group claims (e.g., through a misconfigured identity provider or a token with elevated scopes) can perform LDAP Injection to bypass authorization or extract directory data. Because Chi does not provide built-in LDAP utilities, developers must explicitly sanitize and parameterize any input — including JWT-derived claims — before using them in LDAP queries.

middleBrick can help detect such issues by scanning the unauthenticated attack surface of your Chi service and flagging patterns where external input reaches LDAP-related code paths. While it does not fix the code, its findings include severity ratings and remediation guidance to help prioritize secure handling of JWT claims and LDAP filter construction.

To remediate Ldap Injection risks when combining JWT claims with LDAP queries in Chi, treat all JWT-derived data as untrusted and avoid string concatenation for LDAP filters. Use parameterized LDAP searches or properly escape special LDAP characters. Below are concrete, secure patterns for Go with Chi.

1. Use an LDAP library that supports parameterized filters

Instead of building filters via concatenation, use placeholders and pass values separately. The ldap.v3 library supports this approach:

import (
	"github.com/go-chi/chi/v5"
	"gopkg.in/ldap.v3"
)

func safeUserHandler(ldapConn *ldap.Conn) http.HandlerFunc {
	return func(w http.ResponseWriter, r *http.Request) {
		uid := chi.URLParam(r, "uid")
		// Use parameterized filter with placeholders
		searchReq := ldap.NewSearchRequest(
			"dc=example,dc=com",
			ldap.ScopeWholeSubtree, ldap.NeverDerefAliases, 0, 0, false,
			"(uid=%s)",
			[]string{"cn", "mail"},
			[]interface{}{uid},
		)
		// Perform search and handle response...
	}
}

If your LDAP client library does not support parameterized filters, escape the input using an escaping function. For example, implement or use a function that escapes the following characters according to RFC 4515:

func escapeLDAPFilter(s string) string {
	var b strings.Builder
	for _, r := range s {
		switch r {
		case '\\':
			b.WriteString(`\\`)
		case '*':
			b.WriteString(`\2a`)
		case '(': 
			b.WriteString(`\28`)
		case ')':
			b.WriteString(`\29`)
		case '\x00':
			b.WriteString(`\00`)
		default:
			b.WriteRune(r)
		}
	}
	return b.String()
}

func escapedUserHandler(ldapConn *ldap.Conn) http.HandlerFunc {
	return func(w http.ResponseWriter, r *http.Request) {
		uid := chi.URLParam(r, "uid")
		filter := "(uid=" + escapeLDAPFilter(uid) + ")"
		searchReq := ldap.NewSearchRequest(
			"dc=example,dc=com",
			ldap.ScopeWholeSubtree, ldap.NeverDerefAliases, 0, 0, false,
			filter,
			[]string{"cn", "mail"},
			nil,
		)
		// Perform search and handle response...
	}
}

2. Validate and constrain JWT claims

Ensure strict validation of JWT issuers, audiences, and claim formats. Do not accept arbitrary attributes from the token for LDAP use. For example, if you expect a numeric user ID, validate it explicitly:

uid := chi.URLParam(r, "uid")
if !isValidUserID(uid) {
	http.Error(w, "invalid user identifier", http.StatusBadRequest)
	return
}
// proceed with safe LDAP query

3. Use least-privilege LDAP bind and searches

Configure the LDAP connection used by Chi handlers to bind with a service account that has minimal permissions. This limits the impact of any potential injection by reducing the scope of data an attacker can retrieve or modify.

middleBrick’s scans can verify whether your Chi endpoints expose patterns where JWT claims reach LDAP logic without sanitization, and its findings include prioritized guidance to help you apply these secure coding practices.