diff --git a/ext/curl/interface.c b/ext/curl/interface.c
index fe647dbafd4de..dd4e0db3d77b6 100644
--- a/ext/curl/interface.c
+++ b/ext/curl/interface.c
@@ -1900,7 +1900,6 @@ static zend_result _php_curl_setopt(php_curl *ch, zend_long option, zval *zvalue
 		case CURLOPT_SSLKEYTYPE:
 		case CURLOPT_SSL_CIPHER_LIST:
 		case CURLOPT_USERAGENT:
-		case CURLOPT_USERPWD:
 		case CURLOPT_COOKIELIST:
 		case CURLOPT_FTP_ALTERNATIVE_TO_USER:
 		case CURLOPT_SSH_HOST_PUBLIC_KEY_MD5:
@@ -1998,6 +1997,23 @@ static zend_result _php_curl_setopt(php_curl *ch, zend_long option, zval *zvalue
 			return ret;
 		}
 
+		case CURLOPT_USERPWD:
+		{
+			if (Z_ISNULL_P(zvalue)) {
+				// Authorization header would be implictly set
+				// with an empty string thus we explictly set the option
+				// to null to avoid this unwarranted side effect
+				error = curl_easy_setopt(ch->cp, option, NULL);
+			} else {
+				zend_string *tmp_str;
+				zend_string *str = zval_get_tmp_string(zvalue, &tmp_str);
+				zend_result ret = php_curl_option_str(ch, option, ZSTR_VAL(str), ZSTR_LEN(str));
+				zend_tmp_string_release(tmp_str);
+				return ret;
+			}
+			break;
+		}
+
 		/* Curl nullable string options */
 		case CURLOPT_CUSTOMREQUEST:
 		case CURLOPT_FTPPORT:
diff --git a/ext/curl/tests/gh18458.phpt b/ext/curl/tests/gh18458.phpt
new file mode 100644
index 0000000000000..34be6797e48dd
--- /dev/null
+++ b/ext/curl/tests/gh18458.phpt
@@ -0,0 +1,20 @@
+--TEST--
+GH-18458 authorization header is set despite CURLOPT_USERPWD set to null
+--EXTENSIONS--
+curl
+--SKIPIF--
+<?php
+include 'skipif-nocaddy.inc';
+?>
+--FILE--
+<?php
+
+$ch = curl_init("https://localhost/userpwd");
+curl_setopt($ch, CURLOPT_USERPWD, null);
+curl_setopt($ch, CURLOPT_VERBOSE, true);
+curl_setopt($ch, CURLOPT_RETURNTRANSFER, 1);
+$response = curl_exec($ch);
+var_dump(str_contains($response, "authorization"));
+?>
+--EXPECT--
+bool(false)