fix(security): redesign password reset tokens using crypto/rand with server-side storage

- Replace SHA512-based deterministic token with 32-byte crypto/rand token
- Store tokens server-side with 1-hour expiry and single-use semantics
- Remove genToken (previously broken due to time.Add immutability bug)
- Add CSRF double-submit cookie protection to change/lost/reset forms
- Remove token from form action URL (use hidden fields only, POST body)
- Add MailFrom field and SMTP_FROM env var for configurable sender address
- Add SMTP_PASSWORD_FILE env var for secure SMTP password loading
- Add PUBLIC_URL env var and --public-url flag for configurable reset link domain
- Use generic error messages in handlers to avoid information disclosure

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

change.go

@@ -16,34 +16,50 @@ func checkPasswdConstraint(password string) error {
 
 func changePassword(w http.ResponseWriter, r *http.Request) {
 	if r.Method != "POST" {
-		displayTmpl(w, "change.html", map[string]interface{}{})
+		csrfToken, err := setCSRFToken(w)
+		if err != nil {
+			http.Error(w, "Internal server error", http.StatusInternalServerError)
+			return
+		}
+		displayTmpl(w, "change.html", map[string]interface{}{"csrf_token": csrfToken})
 		return
 	}
 
+	if !validateCSRF(r) {
+		csrfToken, _ := setCSRFToken(w)
+		displayTmplError(w, http.StatusForbidden, "change.html", map[string]interface{}{"error": "Invalid or missing CSRF token. Please try again.", "csrf_token": csrfToken})
+		return
+	}
+
+	renderError := func(status int, msg string) {
+		csrfToken, _ := setCSRFToken(w)
+		displayTmplError(w, status, "change.html", map[string]interface{}{"error": msg, "csrf_token": csrfToken})
+	}
+
 	// Check the two new passwords are identical
 	if r.PostFormValue("newpassword") != r.PostFormValue("new2password") {
-		displayTmplError(w, http.StatusNotAcceptable, "change.html", map[string]interface{}{"error": "New passwords are not identical. Please retry."})
+		renderError(http.StatusNotAcceptable, "New passwords are not identical. Please retry.")
 	} else if len(r.PostFormValue("login")) == 0 {
-		displayTmplError(w, http.StatusNotAcceptable, "change.html", map[string]interface{}{"error": "Please provide a valid login"})
+		renderError(http.StatusNotAcceptable, "Please provide a valid login")
 	} else if err := checkPasswdConstraint(r.PostFormValue("newpassword")); err != nil {
-		displayTmplError(w, http.StatusNotAcceptable, "change.html", map[string]interface{}{"error": "The password you chose doesn't respect all constraints: " + err.Error()})
+		renderError(http.StatusNotAcceptable, "The password you chose doesn't respect all constraints: "+err.Error())
 	} else {
 		conn, err := myLDAP.Connect()
 		if err != nil || conn == nil {
 			log.Println(err)
-			displayTmplError(w, http.StatusInternalServerError, "change.html", map[string]interface{}{"error": err.Error()})
+			renderError(http.StatusInternalServerError, "Unable to process your request. Please try again later.")
 		} else if err := conn.ServiceBind(); err != nil {
 			log.Println(err)
-			displayTmplError(w, http.StatusInternalServerError, "change.html", map[string]interface{}{"error": err.Error()})
+			renderError(http.StatusInternalServerError, "Unable to process your request. Please try again later.")
 		} else if dn, err := conn.SearchDN(r.PostFormValue("login"), true); err != nil {
 			log.Println(err)
-			displayTmplError(w, http.StatusInternalServerError, "change.html", map[string]interface{}{"error": err.Error()})
+			renderError(http.StatusUnauthorized, "Invalid login or password.")
 		} else if err := conn.Bind(dn, r.PostFormValue("password")); err != nil {
 			log.Println(err)
-			displayTmplError(w, http.StatusUnauthorized, "change.html", map[string]interface{}{"error": err.Error()})
+			renderError(http.StatusUnauthorized, "Invalid login or password.")
 		} else if err := conn.ChangePassword(dn, r.PostFormValue("newpassword")); err != nil {
 			log.Println(err)
-			displayTmplError(w, http.StatusInternalServerError, "change.html", map[string]interface{}{"error": err.Error()})
+			renderError(http.StatusInternalServerError, "Unable to process your request. Please try again later.")
 		} else {
 			displayMsg(w, "Password successfully changed!", http.StatusOK)
 		}

csrf.go

@@ -0,0 +1,39 @@
+package main
+
+import (
+	"crypto/rand"
+	"encoding/base64"
+	"net/http"
+)
+
+func generateCSRFToken() (string, error) {
+	b := make([]byte, 32)
+	if _, err := rand.Read(b); err != nil {
+		return "", err
+	}
+	return base64.URLEncoding.EncodeToString(b), nil
+}
+
+func setCSRFToken(w http.ResponseWriter) (string, error) {
+	token, err := generateCSRFToken()
+	if err != nil {
+		return "", err
+	}
+	http.SetCookie(w, &http.Cookie{
+		Name:     "csrf_token",
+		Value:    token,
+		Path:     "/",
+		HttpOnly: false, // must be readable via form hidden field comparison
+		SameSite: http.SameSiteStrictMode,
+	})
+	return token, nil
+}
+
+func validateCSRF(r *http.Request) bool {
+	cookie, err := r.Cookie("csrf_token")
+	if err != nil || cookie.Value == "" {
+		return false
+	}
+	formToken := r.PostFormValue("csrf_token")
+	return formToken != "" && cookie.Value == formToken
+}

ldap.go

@@ -23,6 +23,7 @@ type LDAP struct {
 	MailPort        int
 	MailUser        string
 	MailPassword    string
+	MailFrom        string
 }
 
 func (l LDAP) Connect() (*LDAPConn, error) {

lost.go

@@ -1,54 +1,64 @@
 package main
 
 import (
-	"crypto/sha512"
+	"crypto/rand"
 	"encoding/base64"
-	"encoding/binary"
 	"io"
 	"log"
 	"net/http"
 	"os"
 	"os/exec"
+	"sync"
 	"time"
 
 	"gopkg.in/gomail.v2"
 )
 
-func (l LDAPConn) genToken(dn string, previous bool) string {
+type resetTokenEntry struct {
-	hour := time.Now()
+	dn        string
-	// Generate the previous token?
+	expiresAt time.Time
-	if previous {
+}
-		hour.Add(time.Hour * -1)
+
+var resetTokenStore = struct {
+	mu     sync.Mutex
+	tokens map[string]resetTokenEntry
+}{tokens: make(map[string]resetTokenEntry)}
+
+func generateResetToken() (string, error) {
+	b := make([]byte, 32)
+	if _, err := rand.Read(b); err != nil {
+		return "", err
 	}
+	return base64.URLEncoding.EncodeToString(b), nil
+}
 
-	b := make([]byte, binary.MaxVarintLen64)
+func storeResetToken(token string, dn string) {
-	binary.PutVarint(b, hour.Round(time.Hour).Unix())
+	resetTokenStore.mu.Lock()
+	defer resetTokenStore.mu.Unlock()
 
-	// Search the email address and current password
+	// Clean expired tokens
-	entries, err := l.GetEntry(dn)
+	now := time.Now()
-	if err != nil {
+	for t, e := range resetTokenStore.tokens {
-		log.Println("Unable to generate token:", err)
+		if now.After(e.expiresAt) {
-		return "#err"
+			delete(resetTokenStore.tokens, t)
-	}
-
-	email := ""
-	curpasswd := ""
-	for _, e := range entries {
-		if e.Name == "mail" {
-			email += e.Values[0]
-		} else if e.Name == "userPassword" {
-			curpasswd += e.Values[0]
 		}
 	}
+	resetTokenStore.tokens[token] = resetTokenEntry{
+		dn:        dn,
+		expiresAt: now.Add(time.Hour),
+	}
+}
 
-	// Hash that
+func consumeResetToken(token string) (string, bool) {
-	hash := sha512.New()
+	resetTokenStore.mu.Lock()
-	hash.Write(b)
+	defer resetTokenStore.mu.Unlock()
-	hash.Write([]byte(dn))
+	entry, ok := resetTokenStore.tokens[token]
-	hash.Write([]byte(email))
+	if !ok || time.Now().After(entry.expiresAt) {
-	hash.Write([]byte(curpasswd))
+		delete(resetTokenStore.tokens, token)
-
+		return "", false
-	return base64.StdEncoding.EncodeToString(hash.Sum(nil)[:])
+	}
+	delete(resetTokenStore.tokens, token)
+	return entry.dn, true
 }
 
 func lostPasswordToken(conn *LDAPConn, login string) (string, string, error) {
@@ -64,15 +74,31 @@ func lostPasswordToken(conn *LDAPConn, login string) (string, string, error) {
 		return "", "", err
 	}
 
-	// Generate the token
+	// Generate a cryptographically random token
-	token := conn.genToken(dn, false)
+	token, err := generateResetToken()
+	if err != nil {
+		return "", "", err
+	}
+
+	// Store token server-side with expiration
+	storeResetToken(token, dn)
 
 	return token, dn, nil
 }
 
 func lostPassword(w http.ResponseWriter, r *http.Request) {
 	if r.Method != "POST" {
-		displayTmpl(w, "lost.html", map[string]interface{}{})
+		csrfToken, err := setCSRFToken(w)
+		if err != nil {
+			http.Error(w, "Internal server error", http.StatusInternalServerError)
+			return
+		}
+		displayTmpl(w, "lost.html", map[string]interface{}{"csrf_token": csrfToken})
+		return
+	}
+
+	if !validateCSRF(r) {
+		displayTmplError(w, http.StatusForbidden, "lost.html", map[string]interface{}{"error": "Invalid or missing CSRF token. Please try again."})
 		return
 	}
 
@@ -80,7 +106,7 @@ func lostPassword(w http.ResponseWriter, r *http.Request) {
 	conn, err := myLDAP.Connect()
 	if err != nil || conn == nil {
 		log.Println(err)
-		displayTmplError(w, http.StatusInternalServerError, "lost.html", map[string]interface{}{"error": err.Error()})
+		displayTmplError(w, http.StatusInternalServerError, "lost.html", map[string]interface{}{"error": "Unable to process your request. Please try again later."})
 		return
 	}
 
@@ -88,7 +114,8 @@ func lostPassword(w http.ResponseWriter, r *http.Request) {
 	token, dn, err := lostPasswordToken(conn, r.PostFormValue("login"))
 	if err != nil {
 		log.Println(err)
-		displayTmplError(w, http.StatusInternalServerError, "lost.html", map[string]interface{}{"error": err.Error()})
+		// Return generic message to avoid user enumeration
+		displayMsg(w, "If an account with that login exists, a password recovery email has been sent.", http.StatusOK)
 		return
 	}
 
@@ -96,7 +123,7 @@ func lostPassword(w http.ResponseWriter, r *http.Request) {
 	entries, err := conn.GetEntry(dn)
 	if err != nil {
 		log.Println(err)
-		displayTmplError(w, http.StatusInternalServerError, "lost.html", map[string]interface{}{"error": err.Error()})
+		displayMsg(w, "If an account with that login exists, a password recovery email has been sent.", http.StatusOK)
 		return
 	}
 
@@ -113,16 +140,16 @@ func lostPassword(w http.ResponseWriter, r *http.Request) {
 
 	if email == "" {
 		log.Println("Unable to find a valid adress for user " + dn)
-		displayTmplError(w, http.StatusBadRequest, "lost.html", map[string]interface{}{"error": "We were unable to find a valid email address associated with your account. Please contact an administrator."})
+		displayMsg(w, "If an account with that login exists, a password recovery email has been sent.", http.StatusOK)
 		return
 	}
 
 	// Send the email
 	m := gomail.NewMessage()
-	m.SetHeader("From", "noreply@nemunai.re")
+	m.SetHeader("From", myLDAP.MailFrom)
 	m.SetHeader("To", email)
 	m.SetHeader("Subject", "SSO nemunai.re: password recovery")
-	m.SetBody("text/plain", "Hello "+cn+"!\n\nSomeone, and we hope it's you, requested to reset your account password. \nIn order to continue, go to:\n"+BASEURL+"/reset?l="+r.PostFormValue("login")+"&t="+token+"\n\nBest regards,\n-- \nnemunai.re SSO")
+	m.SetBody("text/plain", "Hello "+cn+"!\n\nSomeone, and we hope it's you, requested to reset your account password. \nIn order to continue, go to:\n"+myPublicURL+"/reset?l="+r.PostFormValue("login")+"&t="+token+"\n\nThis link expires in 1 hour and can only be used once.\n\nBest regards,\n-- \nnemunai.re SSO")
 
 	var s gomail.Sender
 	if myLDAP.MailHost != "" {
@@ -130,7 +157,7 @@ func lostPassword(w http.ResponseWriter, r *http.Request) {
 		s, err = d.Dial()
 		if err != nil {
 			log.Println("Unable to connect to email server: " + err.Error())
-			displayTmplError(w, http.StatusInternalServerError, "lost.html", map[string]interface{}{"error": "Unable to connect to email server: " + err.Error()})
+			displayTmplError(w, http.StatusInternalServerError, "lost.html", map[string]interface{}{"error": "Unable to send password recovery email. Please try again later."})
 			return
 		}
 	} else {
@@ -165,7 +192,7 @@ func lostPassword(w http.ResponseWriter, r *http.Request) {
 
 	if err := gomail.Send(s, m); err != nil {
 		log.Println("Unable to send email: " + err.Error())
-		displayTmplError(w, http.StatusInternalServerError, "lost.html", map[string]interface{}{"error": "Unable to send email: " + err.Error()})
+		displayTmplError(w, http.StatusInternalServerError, "lost.html", map[string]interface{}{"error": "Unable to send password recovery email. Please try again later."})
 		return
 	}
 

main.go

@@ -17,13 +17,14 @@ import (
 	"syscall"
 )
 
-const BASEURL = "https://ldap.nemunai.re"
+var myPublicURL = "https://ldap.nemunai.re"
 
 var myLDAP = LDAP{
 	Host:     "localhost",
 	Port:     389,
 	BaseDN:   "dc=example,dc=com",
 	MailPort: 587,
+	MailFrom: "noreply@nemunai.re",
 }
 
 type ResponseWriterPrefix struct {
@@ -70,8 +71,11 @@ func main() {
 	var bind = flag.String("bind", "127.0.0.1:8080", "Bind port/socket")
 	var baseURL = flag.String("baseurl", "/", "URL prepended to each URL")
 	var configfile = flag.String("config", "", "path to the configuration file")
+	var publicURL = flag.String("public-url", myPublicURL, "Public base URL used in password reset emails")
 	flag.Parse()
 
+	myPublicURL = *publicURL
+
 	// Sanitize options
 	log.Println("Checking paths...")
 	if *baseURL != "/" {
@@ -141,9 +145,25 @@ func main() {
 	if val, ok := os.LookupEnv("SMTP_USER"); ok {
 		myLDAP.MailUser = val
 	}
-	if val, ok := os.LookupEnv("SMTP_PASSWORD"); ok {
+	if val, ok := os.LookupEnv("SMTP_PASSWORD_FILE"); ok {
+		if fd, err := os.Open(val); err != nil {
+			log.Fatal(err)
+		} else if cnt, err := os.ReadFile(val); err != nil {
+			fd.Close()
+			log.Fatal(err)
+		} else {
+			fd.Close()
+			myLDAP.MailPassword = string(cnt)
+		}
+	} else if val, ok := os.LookupEnv("SMTP_PASSWORD"); ok {
 		myLDAP.MailPassword = val
 	}
+	if val, ok := os.LookupEnv("SMTP_FROM"); ok {
+		myLDAP.MailFrom = val
+	}
+	if val, ok := os.LookupEnv("PUBLIC_URL"); ok {
+		myPublicURL = val
+	}
 
 	if flag.NArg() > 0 {
 		switch flag.Arg(0) {
@@ -164,7 +184,7 @@ func main() {
 				log.Fatal(err.Error())
 			}
 
-			fmt.Printf("Reset link for %s: %s/reset?l=%s&t=%s", dn, BASEURL, login, token)
+			fmt.Printf("Reset link for %s: %s/reset?l=%s&t=%s", dn, myPublicURL, login, token)
 			return
 		case "serve":
 		case "server":

reset.go

@@ -3,7 +3,6 @@ package main
 import (
 	"log"
 	"net/http"
-	"strings"
 )
 
 func resetPassword(w http.ResponseWriter, r *http.Request) {
@@ -14,22 +13,46 @@ func resetPassword(w http.ResponseWriter, r *http.Request) {
 
 	base := map[string]interface{}{
 		"login": r.URL.Query().Get("l"),
-		"token": strings.Replace(r.URL.Query().Get("t"), " ", "+", -1),
+		"token": r.URL.Query().Get("t"),
 	}
 
 	if r.Method != "POST" {
+		csrfToken, err := setCSRFToken(w)
+		if err != nil {
+			http.Error(w, "Internal server error", http.StatusInternalServerError)
+			return
+		}
+		base["csrf_token"] = csrfToken
 		displayTmpl(w, "reset.html", base)
 		return
 	}
 
+	renderError := func(status int, msg string) {
+		csrfToken, _ := setCSRFToken(w)
+		base["error"] = msg
+		base["csrf_token"] = csrfToken
+		displayTmplError(w, status, "reset.html", base)
+	}
+
+	if !validateCSRF(r) {
+		renderError(http.StatusForbidden, "Invalid or missing CSRF token. Please try again.")
+		return
+	}
+
 	// Check the two new passwords are identical
 	if r.PostFormValue("newpassword") != r.PostFormValue("new2password") {
-		base["error"] = "New passwords are not identical. Please retry."
+		renderError(http.StatusNotAcceptable, "New passwords are not identical. Please retry.")
-		displayTmplError(w, http.StatusNotAcceptable, "reset.html", base)
 		return
 	} else if err := checkPasswdConstraint(r.PostFormValue("newpassword")); err != nil {
-		base["error"] = "The password you chose doesn't respect all constraints: " + err.Error()
+		renderError(http.StatusNotAcceptable, "The password you chose doesn't respect all constraints: "+err.Error())
-		displayTmplError(w, http.StatusNotAcceptable, "reset.html", base)
+		return
+	}
+
+	// Validate and consume the token (single-use, server-side)
+	token := r.PostFormValue("token")
+	dn, ok := consumeResetToken(token)
+	if !ok {
+		renderError(http.StatusNotAcceptable, "Token invalid or expired, please retry the lost password procedure. Tokens expire after 1 hour.")
 		return
 	}
 
@@ -37,41 +60,22 @@ func resetPassword(w http.ResponseWriter, r *http.Request) {
 	conn, err := myLDAP.Connect()
 	if err != nil || conn == nil {
 		log.Println(err)
-		base["error"] = err.Error()
+		renderError(http.StatusInternalServerError, "Unable to process your request. Please try again later.")
-		displayTmplError(w, http.StatusInternalServerError, "reset.html", base)
 		return
 	}
 
-	// Bind as service to perform the search
+	// Bind as service to perform the password change
 	err = conn.ServiceBind()
 	if err != nil {
 		log.Println(err)
-		base["error"] = err.Error()
+		renderError(http.StatusInternalServerError, "Unable to process your request. Please try again later.")
-		displayTmplError(w, http.StatusInternalServerError, "reset.html", base)
-		return
-	}
-
-	// Search the dn of the given user
-	dn, err := conn.SearchDN(r.PostFormValue("login"), true)
-	if err != nil {
-		log.Println(err)
-		base["error"] = err.Error()
-		displayTmplError(w, http.StatusInternalServerError, "reset.html", base)
-		return
-	}
-
-	// Check token validity (allow current token + last one)
-	if conn.genToken(dn, false) != r.PostFormValue("token") && conn.genToken(dn, true) != r.PostFormValue("token") {
-		base["error"] = "Token invalid, please retry the lost password procedure. Please note that our token expires after 1 hour."
-		displayTmplError(w, http.StatusNotAcceptable, "reset.html", base)
 		return
 	}
 
 	// Replace the password by the new given
 	if err := conn.ChangePassword(dn, r.PostFormValue("newpassword")); err != nil {
 		log.Println(err)
-		base["error"] = err.Error()
+		renderError(http.StatusInternalServerError, "Unable to process your request. Please try again later.")
-		displayTmplError(w, http.StatusInternalServerError, "reset.html", base)
 		return
 	}
 

static/change.html

@@ -3,6 +3,7 @@
 
   <form method="post" action="change">
     {{if .error}}<div class="alert alert-danger" role="alert">{{.error}}</div>{{end}}
+    <input type="hidden" name="csrf_token" value="{{ .csrf_token }}">
     <div class="form-group">
       <input name="login" required="" class="form-control" id="input_0" type="text" placeholder="Login" autofocus>
     </div>

static/lost.html

@@ -3,6 +3,7 @@
 
   <form method="post" action="lost">
     {{if .error}}<div class="alert alert-danger" role="alert">{{.error}}</div>{{end}}
+    <input type="hidden" name="csrf_token" value="{{ .csrf_token }}">
     <div class="form-group">
       <input name="login" required="" class="form-control" id="input_0" type="text" placeholder="Login" autofocus>
     </div>

static/reset.html

@@ -1,8 +1,9 @@
 {{template "header"}}
   <h1 class="display-4">Forgot your password? <small class="text-muted">Define a new one!</small></h1>
 
-  <form method="post" action="reset?l={{ .login }}&t={{ .token }}">
+  <form method="post" action="reset">
     {{if .error}}<div class="alert alert-danger" role="alert">{{.error}}</div>{{end}}
+    <input type="hidden" name="csrf_token" value="{{ .csrf_token }}">
     <div class="form-group">
       <input required="" class="form-control" id="input_0" type="text" placeholder="Email" value="{{ .login }}" disabled="">
     </div>