Fix admin permission check on localized windows (#1552) (#1554)

Fix admin permission check on localized windows (#1552)

(cherry picked from commit 33a5f7e)

Co-authored-by: Michal Pristas <michal.pristas@gmail.com>

changelog/fragments/1666088774-Fix-admin-permission-check-on-localized-windows.yaml

@@ -0,0 +1,31 @@
+# Kind can be one of:
+# - breaking-change: a change to previously-documented behavior
+# - deprecation: functionality that is being removed in a later release
+# - bug-fix: fixes a problem in a previous version
+# - enhancement: extends functionality but does not break or fix existing behavior
+# - feature: new functionality
+# - known-issue: problems that we are aware of in a given version
+# - security: impacts on the security of a product or a user’s deployment.
+# - upgrade: important information for someone upgrading from a prior version
+# - other: does not fit into any of the other categories
+kind: bug-fix
+
+# Change summary; a 80ish characters long description of the change.
+summary: Fix admin permission check on localized windows
+
+# Long description; in case the summary is not enough to describe the change
+# this field accommodate a description without length limits.
+#description:
+
+# Affected component; a word indicating the component this changeset affects.
+component:
+
+# PR number; optional; the PR number that added the changeset.
+# If not present is automatically filled by the tooling finding the PR where this changelog fragment has been added.
+# NOTE: the tooling supports backports, so it's able to fill the original PR number instead of the backport PR number.
+# Please provide it if you are adding a fragment for a different PR.
+pr: 1552
+
+# Issue number; optional; the GitHub issue related to this changeset (either closes or is part of).
+# If not present is automatically filled by the tooling with the issue linked to the PR number.
+issue: 857

internal/pkg/agent/control/server/listener_windows.go

@@ -10,6 +10,7 @@ package server
 import (
 	"net"
 	"os/user"
+	"strings"
 
 	"github.com/pkg/errors"
 
@@ -18,9 +19,14 @@ import (
 	"github.com/elastic/elastic-agent/pkg/core/logger"
 )
 
+const (
+	NTAUTHORITY_SYSTEM   = "S-1-5-18"
+	ADMINISTRATORS_GROUP = "S-1-5-32-544"
+)
+
 // createListener creates a named pipe listener on Windows
-func createListener(_ *logger.Logger) (net.Listener, error) {
-	sd, err := securityDescriptor()
+func createListener(log *logger.Logger) (net.Listener, error) {
+	sd, err := securityDescriptor(log)
 	if err != nil {
 		return nil, err
 	}
@@ -31,7 +37,7 @@ func cleanupListener(_ *logger.Logger) {
 	// nothing to do on windows
 }
 
-func securityDescriptor() (string, error) {
+func securityDescriptor(log *logger.Logger) (string, error) {
 	u, err := user.Current()
 	if err != nil {
 		return "", errors.Wrap(err, "failed to get current user")
@@ -42,11 +48,42 @@ func securityDescriptor() (string, error) {
 	// String definition: https://docs.microsoft.com/en-us/windows/win32/secauthz/ace-strings
 	// Give generic read/write access to the specified user.
 	descriptor := "D:P(A;;GA;;;" + u.Uid + ")"
-	if u.Username == "NT AUTHORITY\\SYSTEM" {
+
+	if isAdmin, err := isWindowsAdmin(u); err != nil {
+		// do not fail, agent would end up in a loop, continue with limited permissions
+		log.Warnf("failed to detect admin: %w", err)
+	} else if isAdmin {
 		// running as SYSTEM, include Administrators group so Administrators can talk over
 		// the named pipe to the running Elastic Agent system process
 		// https://support.microsoft.com/en-us/help/243330/well-known-security-identifiers-in-windows-operating-systems
-		descriptor += "(A;;GA;;;S-1-5-32-544)" // Administrators group
+		descriptor += "(A;;GA;;;" + ADMINISTRATORS_GROUP + ")"
 	}
 	return descriptor, nil
 }
+
+func isWindowsAdmin(u *user.User) (bool, error) {
+	if u.Username == "NT AUTHORITY\\SYSTEM" {
+		return true, nil
+	}
+
+	if equalsSystemGroup(u.Uid) || equalsSystemGroup(u.Gid) {
+		return true, nil
+	}
+
+	groups, err := u.GroupIds()
+	if err != nil {
+		return false, errors.Wrap(err, "failed to get current user groups")
+	}
+
+	for _, groupSid := range groups {
+		if equalsSystemGroup(groupSid) {
+			return true, nil
+		}
+	}
+
+	return false, nil
+}
+
+func equalsSystemGroup(s string) bool {
+	return strings.EqualFold(s, NTAUTHORITY_SYSTEM) || strings.EqualFold(s, ADMINISTRATORS_GROUP)
+}